Oxygen-dominated supra-nano dual-phase catalytic reaction material on a substrate

Abstract

The present invention provides an oxygen-dominated supra-nano dual-phase catalytic reaction material, which includes a uniform oxygen-enriched amorphous shell and a core encapsulated within the uniform oxygen-enriched amorphous shell. This invention exhibits ultrahigh HER performance, a critical reaction in water splitting, making it suitable for application in hydrogen production industries, battery companies, new energy vehicle enterprises, and large power stations.

Description

FIELD OF THE INVENTION

[0001] The present invention generally relates to the fields of electrochemical catalytic materials. More particularly, it relates to an oxygen-dominated supra-nanostructure that offers a pathway to developing an electrocatalyst with exceptionally high activity for hydrogen evolution.BACKGROUND OF THE INVENTION

[0002] The electrochemical splitting of water to produce hydrogen is widely considered as an ideal strategy to decrease the consumption of traditional fossil fuels and be beneficial to the carbon neutral. Especially, the hydrogen evolution reduction (HER) is a crucial reaction involved in electrochemical splitting. In recent years, there have been continuous efforts to develop high-performance electrocatalytic materials for the HER by carefully manipulating their structure or morphology.

[0003] Currently, the commercial HER catalysts used for water splitting are based on Pt nanoparticles dispersed on a carbon substrate, e.g., 20% Pt / C. Moreover, the fabricate method of the current commercial Pt / C is complex and at very high cost. Even though the HER performance of commercial Pt / C satisfies the needs of water splitting, it is desirable to further develop a new catalyst with small overpotential, high electrical conductivity, and high stability, which can further decrease the use of energy.

[0004] Crystal-amorphous supra-nano dual-phase (SNDP) materials are a novel type of nanostructure characterized by a homogeneous and continuous distribution of both crystalline and amorphous regions, with the crystal size and the thickness of the amorphous regions being less than 10 nm. SNDP materials inherit the advantages of both crystalline and amorphous phases and are a prospective alternative to commercial Pt / C HER catalysts, owing to their multicomponent synergetic effect and tremendously large active catalytic interfaces. In addition, SNDP materials with coexisting phases in close contact that differ in terms of their chemical nature have unique interfacial interactions. Such characteristics of SNDP materials fulfil the requirements of superior electrocatalysts.

[0005] Oxygen is an essential component of many materials, with the presence or absence of oxygen affecting material performance. Highly electronegative oxygen affects the local coordination environment of an active site and thus shifts the active site to a higher oxidized state and affects the water absorption ability and Gibbs free energies (ΔGH*) of adsorbed hydrogen (H*).

[0006] In a catalytic reduction process for the HER, it is undesirable for the active center to coordinate directly with oxygen. Therefore, using oxygen to manipulate the electronic structure to enhance hydrogen evolution presents a significant challenge.SUMMARY OF THE INVENTION

[0007] Accordingly, the present invention presents a series of SNDP materials prepared through industrialized magnetron sputtering between a high-entropy amorphous alloy (HEAA) target, Al0.5ZnTiZrSiCuNi, and transition metal targets, specifically Pd, Ir, Pt, Ru, Au, Ag, V, and W. The composition of the SNDP structure can be precisely controlled over a wide range by altering the O content.

[0008] In particular, in a first aspect, the present invention provides an oxygen-dominated supra-nano dual-phase catalytic reaction material on a substrate, which includes a uniform oxygen-enriched amorphous shell and a core encapsulated within the uniform oxygen-enriched amorphous shell. The oxygen-dominated supra-nano dual-phase catalytic reaction material has an intrinsic crystal-amorphous dual-phased structure. The oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10 to 25 mV vs RHE at 10 mA cm−2.

[0009] The crystal phase has a face-centred cubic structure and the amorphous phase has a typical diffused-ring structure.

[0010] In one embodiment, the uniform oxygen-enriched amorphous shell is made from a high-entropy amorphous alloy including AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy. The uniform oxygen-enriched amorphous shell has a thickness of approximately 1-5 nm.

[0011] In one embodiment, the core is made from at least one transition metal including palladium, platinum, iridium, ruthenium, rhodium, gold, silver, or non-noble metal of vanadium, molybdenum, tungsten, and even NiMo, NiW binary alloy. The core is 1-10 nm in diameter.

[0012] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 20-30 at % of Pd, 10-50 at % of O, 1-5 at % of Al, 5-20 at % of Si, 5-20 at % of Ti, 5-20 at % of Ni, 5-20 at % of Cu, 1-15 at % of Zn, and 5-20 at % of Zr.

[0013] In another embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains10-30 at % of Pt, 10-40 at % of O, 5-20 at % of Fe, 5-20 at % of Co, 5-20 at % of Ni, 1-15 at % of Mo, 1-10 at % of P, and 1-10 at % of B.

[0014] In one embodiment, the substrate includes nickel foam, carbon cloth, carbon paper, silicon wafer, porous titanium sheet, titanium foam, or platinum foil.

[0015] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material demonstrates a stability in a 100-hour long-term test at a current density of 20 mA cm−2 in a three-electrode system and can operate steadily for 1000 h at a current density of 500 mA cm−2 in a flow-type membrane exchange assembly alkaline water electrocatalysis cell.

[0016] In another aspect, the oxygen-dominated supra-nano dual-phase catalytic reaction material can used to make a water splitting electrode, including HER electrode and OER electrode.

[0017] In another aspect, the present invention provides a method for fabricating an oxygen-dominated supra-nano dual-phase catalytic reaction material, including co-sputtering a crystal metal target and a high-entropy amorphous alloy target on a substrate by industrial magnetron sputtering, and wherein oxygen gas is introduced during the magnetron sputtering process.

[0018] In one embodiment, the oxygen gas has a flow velocity ranging from approximately 0.01 sccm to 50 sccm.

[0019] In one embodiment, the high-entropy amorphous alloy target is a multi-component alloy comprising AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy.

[0020] In one embodiment, the industrial magnetron sputtering adopts a sputtering temperature at approximately 0.1 to 200° C.

[0021] In one embodiment, the substrate has a rotation speed in the range from 0.1 rpm to 20 rpm during sputtering.

[0022] The present invention provides new SNDP materials based on a transition metal with high-entropy amorphous alloy via industrial magnetron sputtering at ambient temperature by adopting an O domination strategy. The SNDP palladium / high-entropy amorphous alloy (SNDP-Pd@HEAA) of the present invention includes Pd-rich nanocrystalline cores and O-rich amorphous glassy shells, enriched with plenty of next-nearest O coordinated active Pd sites, which actively accelerates hydrogen proton adsorption / desorption, exhibits near zero overpotential (10.16 mV, which is much lower than that of 34.01 mV of commercial 20% Pt / C) at 10 mA cm−2 and superior stability for hydrogen evolution under alkaline conditions. This SNPD nanostructure production and composition manipulation technique, and the next-nearest O coordinated active sites mechanism, establishes a new paradigm for hydrogen evolution reaction catalysts.

[0023] The catalysts of the present invention offer the following advantages: (1) They demonstrate lower overpotential and high stability for hydrogen evolution reaction compared to the existing commercial 20 wt % Pt / C catalysts; (2) By altering the oxygen concentration, the composition of the SNDP structure is precisely regulated over a wide range, overcoming the restricted diversity and constricted compositional regulation range of conventional SNDP structures; and (3) This invention utilizes room-temperature industrial magnetron sputtering technology, which, compared to the techniques used in existing catalysts, has a greater potential for large-scale production.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention are described in more details hereinafter with reference to the drawings, in which:

[0025] FIG. 1A depicts XRD patterns of supra-nano dual-phase palladium / high-entropy amorphous alloy, including SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, o-HEAA, As-HEAA, o-Pd, and As-Pd. FIG. 1B shows scanning electron microscopy of SNDP-Pd@HEAA on carbon cloth. FIG. 1C shows atomic force microscopy of SNDP-Pd@HEAA. FIG. 1D shows SEM energy-dispersive spectroscopy (EDS) mapping of SNDP-Pd@HEAA;

[0026] FIG. 2A shows low-magnification transmission electron microscopy of SNDP-Pd@HEAA. FIG. 2B shows a cross-sectional high-resolution transmission electron microscopy (TEM) image of SNDP-Pd@HEAA. The fast Fourier transformation images in the insets show that the crystal phase has a face-centred cubic structure and the amorphous phase has a typical diffused-ring structure. FIG. 2C depicts the corresponding selected area electron diffraction pattern of SNDP-Pd@HEAA in FIG. 2A;

[0027] FIG. 3A shows three-dimensional reconstructed TEM image of SNDP-Pd@HEAA. FIG. 3B depicts grain-size distribution obtained from multiple TEM images. The plan view is for the x-z plane, and cross-section 1 and cross-section 2 correspond to the x-y plane and y-z plane, respectively. FIG. 3C shows a typical high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image. The arrow shows the direction of the line scan of the energy-dispersive spectroscopy. FIG. 3D depicts line scan intensity of elements in the energy-dispersive spectroscopy along the direction indicated by the arrow in FIG. 3C. FIG. 3E shows three-dimensional atom probe tomography images showing the elemental distribution and multicomponent nature;

[0028] FIG. 4A shows TEM images of SNDP-Pd@HEAA with different O contents. FIG. 4B depicts XRD patterns of SNDP-Pd@HEAA with different O contents;

[0029] FIG. 5A depicts Pd 3d X-ray photoelectron spectroscopy of SNDP-Pd@HEAA. FIG. 5B depicts O 1s X-ray photoelectron spectroscopy of SNDP-Pd@HEAA. FIG. 5C depicts X-ray photoelectron microscopy of SNDP-Pd@HEAA with detailed fitting peaks;

[0030] FIG. 6A depicts Pd K-edge X-ray absorption near-edge structure spectra of SNDP-Pd@HEAA. FIG. 6B depicts corresponding k2-weighted Fourier transform of the X-ray absorption fine structure (EXAFS) spectra. FIG. 6C depicts fitting of the k2-weighted Fourier transform of EXAFS spectra at the Pd K-edge of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA;

[0031] FIG. 7 depicts wavelet transforms for k2-weighted EXAFS signals at the Pd K-edge of SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, Pd foil and PdO;

[0032] FIG. 8A depicts XRD patterns of SNDP-M@HEAA samples (M=Au, Ag, W, Pt, Ru, Ir, Pd). FIG. 8B shows TEM images of SNDP-M@HEAA samples;

[0033] FIG. 9A depicts polarisation curves of samples deposited on glassy carbon obtained at a scan rate of 5 mV s−1 with iR correction, and FIG. 9B polarisation curves of the SNDP-Pd@HEAA samples with different O contents in 1 M KOH with iR correction;

[0034] FIG. 10A depicts corresponding Tafel plots of FIG. 9A. FIG. 10B depicts corresponding Tafel plots of FIG. 9B;

[0035] FIG. 11 depicts electrochemical impedance spectroscopy of SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, o-Pd, As-Pd, o-HEAA, As-HEAA, and 20% Pt / C at an overpotential of 100 mV in 1 M KOH solution at room temperature;

[0036] FIG. 12A depicts cyclic voltammograms in the region of 0-0.1 V vs. RHE at various scan rates for SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, o-Pd, As-Pd, o-HEAA, As-HEAA, 20% Pt / C. FIG. 12B depicts calculated electrochemical double-layer capacitance for the as-prepared materials;

[0037] FIG. 13A shows structural configurations of SNDP models without and with O. FIG. 13B depicts DFT-calculated ΔEH2O of H2O molecules at various sites in the interface models with and without O element. For reference, ΔEH2O of the Pt(111) surface is marked by a grey dashed line. FIG. 13C depicts DFT calculation of ΔEH2O of H2O molecules at Pd sites in crystal, amorphous, and interface models with and without elemental O. For reference, ΔEH2O of the Pt(111) surface is marked by a grey dashed line;

[0038] FIG. 14 depicts DFT simulations of atomic configurations and the corresponding electron density difference after H2O adsorption at Pd, Ti, Zr, and Al sites in the interface models with and without elemental O. dx-o represents the bonding distances between the O atom at the H2O and Pd, Ti, Zr, and Al sites;

[0039] FIG. 15 depicts p-PDOS of the O atom in an H2O molecule after H2O adsorption onto Pd, Ti, Zr, and Al sites in the interface models with and without elemental O, respectively. The black dashed lines at zero energy indicate the Fermi level (EF);

[0040] FIG. 16A depicts representative local chemical environment after H* adsorption at Pd top sites in crystalline / amorphous interface models without O coordination, with nearest O coordination, and with next-nearest O coordination. FIG. 16B depicts ΔGH* profiles for Pd sites in the crystal, amorphous, and crystalline / amorphous interface models without O coordination, with nearest O coordination, and with next-nearest O coordination, respectively. FIG. 16C depicts local chemical environment after H* adsorption at Pd top sites in the crystal and amorphous models without O coordination, with nearest O coordination, and with next-nearest O coordination;

[0041] FIG. 17A depicts DFT simulation results of the two-dimensional electron density difference and equilibrium distance for Pd-Ti, Pd-O, and Pd-Ti (O). FIG. 17B depicts d-orbital partial density of states (d-PDOS) of Pd catalytic sites at the interface without O coordination, with nearest O coordination, and with next-nearest O coordination. The black dashed line indicates the Fermi level. The solid straight lines indicate the corresponding d-band centres;

[0042] FIG. 18A depicts Gibbs free energy (ΔGH*) profiles for various bridge and hollow sites in crystalline / amorphous interface models without elemental O and with elemental O. FIG. 18B depicts local chemical environment of various H* adsorption sites (bridge and hollow) in crystalline / amorphous interface models without and with elemental O;

[0043] FIG. 19A depicts relationship between the catalytic performance and the O content of SNDP-Pd@HEAA, showing an improvement in the hydrogen evolution reaction performance as the oxygen content increases. FIG. 19B depicts electrochemical impedance spectroscopy of SNDP-Pd@HEAA samples with different O contents in 1 M KOH solution at an overpotential of 100 mV and room temperature. FIG. 19C depicts cyclic voltammograms in the region of 0-0.1 V vs. RHE at various scan rates for SNDP-Pd@HEAA samples with different oxygen atomic contents;

[0044] FIG. 20 depicts performance comparison of catalysts at the current density of 10 mA cm−2 in alkaline solutions;

[0045] FIG. 21A depicts long-time performances of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA at a constant current density of 20 mA cm−2 in alkaline solutions. FIG. 21B depicts X-ray photoelectron microscopy of As-SNDP-Pd@HEAA after 100 h in 1 M KOH;

[0046] FIG. 22A depicts polarisation curves of SNDP-Pt@HEAA and As-SNDP-Pt@HEAA in 1 M KOH with iR correction. FIG. 22B depicts polarisation curves of SNDP-Au@HEAA and As-SNDP-Au@HEAA in 1 M KOH with iR correction. FIG. 22C depicts polarisation curves of SNDP-Ag@HEAA and As-SNDP-Ag@HEAA in 1 M KOH with iR correction. FIG. 22D depicts polarisation curves of SNDP-W@HEAA and As-SNDP-W@HEAA in 1 M KOH with iR correction. FIG. 22E depicts polarisation curves of SNDP-Ir@HEAA, As-SNDP-Ir@HEAA, and IrO2 in 1 M KOH with iR correction. FIG. 22F depicts polarisation curves of SNDP-Ru@HEAA and As-SNDP-Ru@HEAA in 1 M KOH with iR correction; and

[0047] FIG. 23 depicts long-term durability of the SNDP-Pd@HEAA / SNDP-Ir@HEAA cell at a constant current density of 0.5 A cm−2.DETAILED DESCRIPTION

[0048] Fabricating excellent hydrogen evolution reaction catalysts with near-zero overpotential at a large scale is challenging. The supra-nano dual-phase (SNDP) structure, which incorporates the optimal benefits of both crystalline and amorphous phases with a multicomponent synergy effect and enormously large active catalytic inter-phases, is a promising commercial platinum on carbon (Pt / C) alternative. However, a restricted variety of elements are readily available for fabricating SNDP structures and the compositional regulation of them is limited.

[0049] Accordingly, the present invention provides an oxygen-dominated supra-nano dual-phase catalytic reaction material on a substrate, which includes a uniform oxygen-enriched amorphous shell and a core encapsulated within the uniform oxygen-enriched amorphous shell. The oxygen-dominated supra-nano dual-phase catalytic reaction material has an intrinsic crystal-amorphous dual-phased structure. The oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10 to 25 mV vs RHE at 10 mA cm−2.

[0050] Preferably, the oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10.16 mV vs RHE at 10 mA cm−2.

[0051] In one embodiment, the uniform oxygen-enriched amorphous shell is made from a high-entropy amorphous alloy including AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy. The uniform oxygen-enriched amorphous shell has a thickness of approximately 1-5 nm.

[0052] In one embodiment, the core is made from at least one transition metal including palladium, platinum, iridium, ruthenium, rhodium, gold, silver, or non-noble metal of vanadium, molybdenum, tungsten, and even NiMo, NiW binary alloy. The core is 1-10 nm in diameter.

[0053] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 20-30 at % of Pd, 10-50 at % of O, 1-5 at % of Al, 5-20 at % of Si, 5-20 at % of Ti, 5-20 at % of Ni, 5-20 at % of Cu, 1-15 at % of Zn, and 5-20 at % of Zr.

[0054] Preferably, O concentration of 42.24 at. % had the best electrocatalytic performance. The oxygen-dominated supra-nano dual-phase catalytic reaction material contains 25.12 at % of Pd, 42.24 at % of O, 2.74 at % of Al, 3.35 at % of Si, 2.9 at % of Ti, 3.99 at % of Ni, 4.62 at % of Cu, 8.62 at % of Zn, and 6.41 at % of Zr.

[0055] In another embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 10-30 at % of Pt, 10-40 at % of O, 5-20 at % of Fe, 5-20 at % of Co, 5-20 at % of Ni, 1-15 at % of Mo, 1-10 at % of P, and 1-10 at % of B.

[0056] In one embodiment, the substrate includes nickel foam, carbon cloth, carbon paper, silicon wafer, porous titanium sheet, titanium foam, or platinum foil.

[0057] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material demonstrates a stability in a 100-hour long-term test at a current density of 20 mA cm−2 in a three-electrode system and can operate steadily for 1000 h at a current density of 500 mA cm−2 in a flow-type membrane exchange assembly alkaline water electrocatalysis cell.

[0058] The intriguing crystal / amorphous dual-phase structure and large number of next-nearest O coordinated active sites at interfaces give rise to a near-zero value of ΔGH* and a strong H2O adsorption capability that promote H2O adsorption and hydrogen / proton adsorption and thus contribute to the excellent HER performance of SNDP-Pd@HEAA.

[0059] The crystal region is enriched with the crystal target's elements, while the amorphous region is highly enriched with oxygen. All elements from the target are uniformly distributed within the material. The content of the crystal target's elements in the crystal region is higher than in the amorphous region. The atomic ratio of the crystal target's elements ranges from approximately 20 at % to 80 at % in the crystal region and from approximately 0 at % to 40 at % in the amorphous region. The atomic ratio of oxygen ranges from approximately 0.01 at % to 30 at % in the crystal region and from approximately 10 at % to 70 at % in the amorphous region. The atomic ratio of all elements from the target ranges from approximately 0.01 at % to 30 at %.

[0060] In one embodiment, the oxygen content of the crystal region is much lower than that in the amorphous region.

[0061] SNDP-Pd@HEAA has a homogeneously distributed three-dimensional structure that comprises a Pd-rich crystalline core with a diameter of approximately 1-10 nm and an HEAA-enriched homogeneous amorphous shell with a thickness of approximately 1-5 nm.

[0062] In one embodiment, the SNDP material is SNDP palladium / high-entropy amorphous alloy (SNDP-Pd@HEAA). The SNDP-Pd@HEAA, with Pd-rich grains (4.76 nm in diameter) and uniform O-enriched amorphous shells (thickness of approximately 1.2 nm), exhibited a near-zero overpotential (10.16 mV at 10 mA cm−2) and is thus a prospective alternative to commercial Pt / C HER catalysts under alkaline conditions.

[0063] The size of the nanograins and the thickness of the amorphous layer in the catalyst can be easily adjustable by simply applying different power to the targets and the rotation speed of the receiving substrate during the magnetron sputtering process. For instance, the power source applied to the metal target is radio-frequency (RF) power supply. The power source applied to the high-entropy amorphous alloy target is direct-current (DC) power supply. The RF power supply is in the range from 30 to 200 W, and power of the DC power supply is in the range from 35 to 225 W.

[0064] When directly used as an HER electrocatalyst without further post-treatment, SNDP-Pd@HEAA has an overpotential close to zero (10.16 mV at 10 mA cm−2) under alkaline conditions. The long-term durability of SNDP-Pd@HEAA in alkaline media can be attributed to the restricted oxidation tendency of O-dominated HEAA.

[0065] In one embodiment, the SNDP structure can be deposited on various substrates based on its applications. For instance, the substrates may include nickel foam, carbon cloth, carbon paper, silicon wafer, titanium sheet, or platinum foil.

[0066] All SNDP samples deposited uniformly on the conductive substrate via magnetron sputtering exhibited similarly smooth surfaces. However, the electrochemically active surface area of SNDP-Pd@HEAA with flat and smooth surface, was 2.75 times greater than that of commercial 20 wt % Pt / C containing ultrasmall nanoparticles.

[0067] In another aspect, the oxygen-dominated supra-nano dual-phase catalytic reaction material can used to make a water splitting electrode.

[0068] In another aspect, the present invention also presents an industrialized method of developing SNDP nanostructures with near-zero potential for widespread electrocatalytic applications and new insight into next-nearest O coordinated active sites.

[0069] In particular, the present invention provides a method for fabricating an oxygen-dominated supra-nano dual-phase catalytic reaction material. The method includes co-sputtering a crystal metal target and a high-entropy amorphous alloy target on a substrate by industrial magnetron sputtering. Oxygen gas is introduced during the magnetron sputtering process.

[0070] The crystal metal target and the high-entropy amorphous alloy target can be combined arbitrarily according to the final application scenarios and operation condition. The application scenarios are hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, hydrogen oxidation reaction, carbon dioxide reduction reaction, water splitting, proton exchange membrane fuel cell materials and metal-air batteries. The operation condition can be in a wide range of pH value.

[0071] The high-entropy amorphous alloy target is multi-component alloy which is easy to form amorphous structure during the sputtering process, which need some easily oxidized elements and some non-metallic elements, such as AlZnTiZrSiCuNi-containing alloy.

[0072] The industrial magnetron sputtering adopts a sputtering temperature at approximately 0.1 to 200° C.EXAMPLEExample 1—Materials and MethodsMaterials

[0073] Raw element granules of aluminium (Al), zinc (Zn), titanium (Ti), zirconium (Zr), silicon (Si), copper (Cu), and nickel (Ni) with a purity higher than 99.95% were mixed by China Material Technology Co., Ltd to achieve the high-entropy amorphous alloy (HEAA) sputtering target with a theoretical atomic composition (at %) of Al0.5ZnTiZrSiCuNi. The pure palladium (Pd) target with a purity higher than 99.99% was purchased from Angstrom Engineering Inc. Co., Ltd. Analytical grade potassium hydroxide (KOH), and absolute ethanol were supplied by Sigma Aldrich. All of the solutions were prepared with Milli-Q water (18.2 MΩcm).Material Characterization

[0074] The samples were characterised through scanning electron microscopy (SEM, Philips XL-30 FESEM), atomic force microscopy (AFM, Bruker Icon), and high-resolution transmission electron microscopy (TEM, JEOL TEM 2100F FEG operated with an accelerating voltage of 200 kV). Atomic-resolution scanning transmission electron microscopy (STEM) images and energy-dispersive spectrometry (EDS) maps were acquired on a Titan FEI Themis G60-300 S / TEM (fitted with a high-brightness field emission gun (X-FEG), probe CS corrector, and super-X EDS with four windowless silicon drift detectors). X-ray diffraction (XRD) patterns were collected using an X-ray diffractometer (Rigaku SmartLab) with Cu Kα radiation (λ=1.5418 Å). Three-dimensional atomic probe tomography (APT) characterisation was performed using a local electrode atom probe (CAMECA LEAP 5000 XR). The APT experiments were conducted at 60 K in laser mode with a laser energy of 50 pJ and a pulse rate of 125 kHz, and the detection rate was 0.3%. The corresponding three-dimensional reconstructions and data analysis were performed using Imago Visualization and Analysis Software (IVAS, version 3.8.2). Both TEM and APT specimens were prepared on an FEI focused ion beam / scanning electron microscope (FIB / SEM) adopting the lift-out and annular milling method. In the preparation of stability-tested TEM and APT specimens, SNDP-Pd@HEAA was sputtered on nickel foam. The leached metallic ions in the stability test were measured through inductively coupled plasma-optical emission spectrometry (ICP-OES) (Optima ICP-OES Spectrometer, PerkinElmer) with a 10-times diluted solution. (The results were corrected with the dilution factor.) X-ray photoelectron microscopy was performed on an ESCALAB 250 photoelectron spectrometer (ThermoFisher Scientific) with Al Ka (1486.6 eV) as the X-ray source set at 150 W and a pass energy of 30 eV for high-resolution scanning. The base pressure was 3 ×10−9 mbar, and the binding energies were referenced to the C1s line at 284.8 eV from adventitious carbon. The X-ray absorption near edge structure and extended X-ray absorption fine structure experiments on the SNDP-Pd@HEAA catalysts were carried out at the BL14W1 beamline of the Shanghai Synchrotron Radiation Facility. The data were collected in fluorescence mode using a Lytle detector while the corresponding reference sample was measured in transmission mode. The incident beam was monochromatised using a Si(111) fixed-exit, double-crystal monochromator, and a harmonic rejection mirror was applied to cut off the high-order harmonics. The obtained X-ray absorption fine structure data were processed in Athena (version 0.9.26) for background, pre-edge line, and post-edge line calibrations. Fourier transformed fitting was then carried out in Artemis (version 0.9.26). Adopting a k3 weighting scheme, a k-range of 3-14 Å−1 and an R range of 1 to approximately 3 Å were used in the fitting for the Pd foil and a k-range of 3-11 Å−1 and an R range of 1 to approximately 3.5 Å were used in the fitting for the SNDP-Pd@HEAA samples. Three parameters, the coordination number, bond length, and E0 shift (CN, R, ΔE0), were freely fitted for a set Debye-Waller factor σ2. In the wavelet transform analysis, χ(k) exported from Athena was imported into Hama Fortran code. The parameters were an R range of 0-4 Å, a k-range of 0-11 Å−1 for Pd, and a k-weight of 3. A Morlet function with κ=10 and σ=1 was used as the mother wavelet to give the overall distribution.Electrochemical Measurements

[0075] The SNDP-Pd@HEAA film was deposited on carbon cloth and glassy carbon electrode (Φ4 mm) with a thickness of approximately 350 nm for electrochemical investigation. Electrochemical measurements were conducted in 1.0 M KOH solution at room temperature on a CHI660e electrochemical station with a three-electrode cell system. SNDP-Pd@HEAA, a Hg / HgO electrode, and a graphite rod were used as the working, reference, and counter electrodes, respectively.

[0076] To more precisely measure the intrinsic overpotential of the deposited films, linear sweep voltammetry (LSV) for the samples deposited on glassy carbon electrode was recorded at a scan rate of 5 mV s−1 to obtain the polarisation curves. Electrochemical impedance spectroscopy (EIS) was carried out from 100 kHz to 0.1 Hz. A series of cyclic voltammograms were obtained in the potential range of 0-0.1 V (vs. RHE) with scan rates ranging from 10 to 80 mV s−1 at non-faradaic overpotentials to demonstrate the current charging and discharging capacitance in estimating the double-layer capacitance (Cdl). The electrochemical surface area was obtained as Cdl / Cs, where Cdl is the measured double-layer capacitance and Cs is the specific capacitance. In the present invention, a Cs value of 0.04 mF cm−2 was assumed owing to the flat surface of SNDP-Pd@HEAA. Long-term stability tests for samples on carbon cloth were performed by continuously applying a current density of 20 and 200 mA cm−2 to the working electrode adopting a chronoamperometry method without iR loss correction. The current density was calculated from the geometric surface areas. All of the data presented were corrected for iR losses and background current, and the potentials were later converted to the reversible hydrogen electrode (RHE) scale.RHE Calibration

[0077] All of the potentials in the present invention were calibrated and converted to the RHE scale. The calibration was performed in a high-purity hydrogen-saturated electrolyte with a Pt wire and carbon rod as the working electrode and counter electrode, respectively. The Hg / HgO electrode was used as the reference electrode in 1 M KOH. The CV were measured at a scan rate of 1 mV s−1. The average of the two potentials at which the current reached zero was taken as the thermodynamic potential for the hydrogen electrode reactions. In 1 M KOH, ERHE=EHg / HgO+0.9280.DFT Calculations

[0078] Density functional theory (DFT) calculations were performed using the Cambridge Sequential Total Energy Package (CASTEP) module in Materials Studio. The generalised gradient approximation method with the Perdew-Burke-Ernzerh function (GGA-PBE) was used to describe the exchange and corrections of atomic interactions and the ultrasoft pseudo-potential method was used to describe the interactions between valence electrons and ionic cores. A plane-wave basis set with a cutoff energy of 400 eV was assigned. The Brillouin zone was sampled using a Monkhorst-Pack grid for the crystal model and a Γ point for the amorphous and crystalline / amorphous interface models. The tolerances of energy, force, and displacement for structural optimisation were 1.0×10−6 eV / atom, 0.02 eV / Å, and 0.001Å, respectively. The self-consistent field was set at 1.0×10−5 eV / atom. The H2O adsorption energies (ΔEH2O ) at the surface of catalysts were calculated according toΔ⁢EH2⁢O=Esurf+H2⁢O-Esurf-EH2⁢O(1)where Esurf and Esurf+H<sub2>2< / sub2>O are the total energies of the surface before and after H2O adsorption. EH<sub2>2< / sub2>O represents the energy of a free water molecule.The Gibbs free energies for hydrogen adsorption (ΔGH*) were calculated according to:Δ⁢GH*=Δ⁢EH*+Δ⁢Z⁢P⁢E-T⁢Δ⁢S(2)where ΔEH*, ΔZPE, T, and ΔS are the binding energy, zero point energy change, temperature, and entropy change of the H* adsorption system, respectively.The vibrational entropy of H* in the adsorbed state is generally negligible. ΔS was thus calculated as:Δ⁢S=SH*-12⁢SH2≈-12⁢SH2(3)where SH<sub2>2 < / sub2>is the entropy of the gas phase H2 under standard conditions.Moreover, ΔZPE was calculated as:Δ⁢Z⁢P⁢E=Z⁢P⁢EH*-12⁢Z⁢P⁢EH2(4)Hence, the Gibbs free energy of the adsorbed state of H* was calculated using the simplified equation:Δ⁢GH*=Δ⁢EH*+0.24 eV(5)A series of atomistic models were built to study the H2O adsorption energies and the Gibbs free energies of H* for various active sites in different regions of HEAA samples with and without elemental O. The modelling was consistent with the experimental results. Specifically, three representative models with crystal, amorphous, and crystalline / amorphous dual-phase structures (referred to as Crystal, MG and Interface, respectively) were constructed.To reveal the effect of O addition on the hydrogen evolution reaction performance, three other models with crystal, amorphous, and dual crystalline / amorphous phase structures were constructed with O addition. To obtain reliable configurations of the amorphous models, first, all atoms were randomly assigned into cubic supercells and periodic boundary conditions were applied in three directions. The amorphous models were then well relaxed and optimised to remove artificial factors. The crystalline / amorphous interface models were built by combining the crystal and amorphous models followed by further relaxation and optimisation. Using the optimised crystal, amorphous, and interface models established above, a vacuum gap approximately 15 Å wide was introduced to investigate the hydrogen evolution reaction performance of various active sites on the surfaces of these models. Hence, the H2O adsorption energies and H* Gibbs free energies of six representative models (crystal, amorphous, and interface models with and without O addition) could be investigated to unveil the atomistic mechanism that accounts for the improved hydrogen evolution reaction performance of the catalyst of the present invention.Example 2—Preparation of SNDP-Pd@HEAA CatalystsThe catalyst with novel supra-nano dual-phase structure was synthesized by introducing a large amount of oxygen innovatively. In this example, SNDP-Pd@HEAA catalysts were synthesized using double-target magnetron sputtering, a bottom-up, industrialized method that enables the large-scale production of a wide variety of nanomaterials. The fabrication method used in this work was magnetron co-sputtering (Angstrom Engineering Inc. Co., Ltd). The background vacuum was 4×10−7 Torr. HEAA and Pd targets were used for co-sputtering. The SNDP-Pd@HEAA was then deposited on different substrates (Si(001), carbon cloth, and nickel foam, Pt foil) simultaneously for different purposes.

[0086] The thickness of the films was easily controlled by the sputtering time and the composition of the films was controlled by tuning the difference in substrate-to-target distances. During co-sputtering process, the power supplied to the HEAA target with a direct-current source was set at 135 W; the power supplied to the Pd target with a radio-frequency source was set at 105 W; the flow velocity of Ar was 20 sccm and that of O2 was 1 sccm; the chamber pressure was 3 mTorr; the deposition rate was approximately 6 nm min−1; and the temperature of the substrate was below 50° C.

[0087] Additionally, a series of SNDP-M@HEAA materials (M=Ir, Pt, Ru, Au, Ag, or W) were prepared by adopting the same method.Example 3—Characterization of the SNDP-Pd@HEAA Catalysts

[0088] Referring to FIG. 1A, the X-ray diffraction patterns of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA catalysts had a broad diffraction peak without strong Bragg crystalline diffraction. This peak was much narrower than the diffraction peak of the amorphous HEAA, indicating the amorphous and ultra-small nanocrystalline nature of the catalysts. The SEM images of SNDP-Pd@HEAA deposited on carbon cloth revealed a smooth surface (FIG. 1B). Additionally, atomic force microscopy revealed the ultra-smooth surface of SNDP-Pd@HEAA, exhibiting a roughness of only approximately 1.36 nm (FIG. 1C).

[0089] The components of SNDP-Pd@HEAA were identified through EDS mapping. Referring to FIG. 1D, the SNDP-Pd@HEAA contained 25.12 at % Pd, 42.24 at % O , 2.74 at % Al, 3.35 at % Si, 2.9 at % Ti, 3.99 at % Ni, 4.62 at % Cu, 8.62 at % Zn, and 6.41 at % Zr.

[0090] The TEM image of FIG. 2A showed a homogeneous distribution of nanoparticles surrounded by a thin amorphous layer. The high-resolution STEM image in FIG. 2B further revealed an amorphous / nanocrystalline SNDP structure, such structure featured uniformly dispersed nanograins were approximately 4.5 nm in diameter with a face-centred cubic crystalline structure. Surrounding the nanocrystals was an amorphous layer approximately 1.2 nm in thickness. Referring to FIG. 2C, the above findings aligned with the selected area electron diffraction (SAED) pattern, which displayed an amorphous ring alongside several crystalline rings. These crystalline rings could be indexed to multi-crystal face-centered cubic Pd with random orientations.

[0091] The three-dimensional reconstructed TEM image showed the same SNDP structure from the horizontal region to the cross-sectional region (FIG. 3A), indicating the homogeneous SNDP structure of the SNDP-Pd@HEAA in three dimensions, which differed greatly from the granular / columnar structure of conventional sputtered films. A statistical examination of the grain-size distribution of more than 300 nanocrystals showed that the grain size had a mean value of approximately 4.76 nm, and that more than 94.47% of the nanocrystals were within the size range of 3-6 nm (FIG. 3B). A cross-sectional high-angle annular dark-field STEM (HAADF-STEM) image provided additional evidence of the nanograin nature of SNDP-Pd@HEAA (FIG. 3C). The corresponding indexed EDS line scan compositional profile (FIG. 3D) displayed sharp compositional transitions between Pd and O across the amorphous and crystalline regions. Specifically, the Pd content was higher in the nanograin regions compared to the amorphous regions, whereas the O content showed an inverse distribution relative to Pd. The other elements (e.g., Al, Zn, Ti, Zr, Si, Cu, and Ni) were homogeneously distributed in the SNDP film.

[0092] FIG. 3E showed a two-dimensional tomographic reconstruction from a typical three-dimensional atom probe tomography dataset, revealing the content variations of all the elements across a truncated plane. Specifically, the crystalline and amorphous phases were respectively enriched in Pd and O whereas Al, Zn, Ti, Zr, Si, Cu, and Ni were distributed uniformly across the two phases as regular solutes.

[0093] For comparison, the samples obtained under the same conditions except for the introduction of oxygen during the synthesis process were denoted as As-SNDP-Pd@HEAA. The pure HEAA film and pure Pd film were prepared by single-target sputtering under the same conditions. For comparison, the samples with different contents of oxygen were prepared under different flow velocities of O2. The As-SNDP-Pd@HEAA sample had a crystal-amorphous SNDP structure similar to that of SNDP-Pd@HEAA. The o-Pd and o-HEAA samples had a pure PdO crystal and purely amorphous nature, respectively. Similarly, the As-Pd and As-HEAA samples had a pure Pd crystal and purely amorphous nature, respectively.

[0094] The SNDP-Pd@HEAA samples with varying oxygen contents were produced by adjusting the oxygen gas flow rate. The elemental compositions of these samples were determined using SEM-EDS and are summarized in Table 1. The O content was positively correlated with the flow rate of the oxygen gas.TABLE 1Elemental compositions of SNDP-Pd@HEAA sampleswith different O contents obtained by SEM-EDSO2PdAlCuNiTiZnZrSiOflow rate(at %)(at %)(at %)(at %)(at %)(at %)(at %)(at %)(at %)0sccm39.003.907.406.175.6912.3911.985.757.720.15sccm36.983.727.495.875.1911.2410.865.4013.250.3sccm34.183.296.655.485.9710.1210.155.4118.750.5sccm33.883.785.884.484.078.634.825.1529.310.75sccm27.652.815.104.593.759.607.343.7435.431sccm24.522.744.623.992.908.826.413.7542.242sccm23.992.023.753.252.435.148.323.3947.713.5sccm23.511.222.382.151.011.179.732.0356.80

[0095] Referring to FIG. 4A, detailed TEM analysis showed that the SNDP structure was consistently obtained across the entire range of oxygen contents investigated. The SNDP-Pd@HEAA samples with different O contents had similar broad diffraction peaks with drift of the peak positions (FIG. 4B).

[0096] To determine the chemical states of the elements in SNDP-Pd@HEAA, XPS was conducted, as shown in FIGS. 5A-5C. The Pd 3d spectrum had two peaks located at 340.64 eV (Pd 3d3 / 2) and 335.32 eV (Pd 3d5 / 2), which were characteristic of metallic Pd (Pd0)10. Additionally, there was a slight shift towards higher energy compared to pure Pd metal, likely due to the surrounding amorphous structure. The introduction of oxygen to the SNDP caused a down-shift in the Pd 3d signals, indicating that the d-band electron structure of SNDP-Pd@HEAA could be easily regulated by oxygen atoms. Similarly, the binding energies at 951.67 and 931.85 eV revealed unitary metallic states of Cu. The Ni 2p XPS spectra showed that most of Ni were in the metallic state and only a little of the Ni were oxidated. In contrast, the Si2p XPS spectra revealed that most of the silicon was in oxidized states, with only a small amount remaining in the zero-valence state. The Al2p, Ti2p, Ti2p and Zr3d XPS spectra indicated that all these elements were in the oxidation states. The O1s spectrum could be deconvoluted into multiple peaks, indicating the complex coordination state of oxygen with other atoms in the SNDP-Pd@HEAA. These results further illustrated that the introduced oxygen preferred to react with the elements of HEAA, and that HEAA could protect the Pd from oxidation, leading to an enrichment of oxygen in the amorphous region.

[0097] Moreover, the X-ray absorption fine structure (XAFS) was measured to clarify the electronic structures and atomic structures of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA. Referring to FIG. 6A, the X-ray absorption near-edge structure spectra at the Pd K-edge indicated that elemental Pd was predominantly in the metallic state of Pd0 in both SNDP-Pd@HEAA and As-SNDP-Pd@HEAA. The significant increase in oxygen content did not affect the valence state of Pd, consistent with the previously mentioned XPS results. The corresponding Pd K-edge extended X-ray absorption fine structure (EXAFS) (FIG. 6B) and its fitting analysis (FIG. 6C and Tables 2 and 3) revealed the existence of Pd-Pd and Pd-M (M=Ni, Cu, Zn) coordination in both SNDP-Pd@HEAA and As-SNDP-Pd@HEAA.TABLE 2EXAFS fitting parameters at the Pd K-edge for SNDP-Pd@HEAA (S02 = 0.82)ShellCNR (Å)σ2ΔE0R factorPd foilPd-Pd122.74 ± 0.010.00556.5 ± 0.40.0042PdOPd-O3.8 ± 0.22.03 ± 0.010.00202.8 ± 1.10.0038Pd-Pd4.6 ± 0.33.06 ± 0.010.0033Pd-Pd14.5 ± 0.43.46 ± 0.010.0020SNDP-Pd-O0.3 ± 0.22.02 ± 0.060.00140.8 ± 1.10.0106Pd@HEAAPd-M1.0 ± 0.22.58 ± 0.010.0016Pd-Pd7.3 ± 0.52.68 ± 0.020.0100CN: coordination number; R: bond distance; σ2: Debye-Waller factor; ΔE0: inner potential correction; R factor: goodness of fit; M = Cu, Ni, Zn.TABLE 3EXAFS fitting parameters at the Pd K-edge forAs-SNDP-Pd@HEAA (S02 = 0.84)ShellCNR (Å)σ2ΔE0R factorPd foilPd-Pd122.74 ± 0.010.00564.0 ± 0.30.0021PdOPd-O3.8 ± 0.22.02 ± 0.010.00142.8 ± 1.10.0038Pd-Pd4.6 ± 0.33.06 ± 0.010.0033Pd-Pd14.5 ± 0.43.46 ± 0.010.0020As-SNDP-Pd-M6.7 ± 0.42.60 ± 0.010.0198−4.4 ± 1.3 0.0095Pd@HEAAPd-Pd4.0 ± 0.42.75 ± 0.010.0088Pd-Zr0.6 ± 0.23.00 ± 0.010.0014CN: coordination number; R: bond distance; σ2: Debye-Waller factor; ΔE0: inner potential correction; R factor: goodness of fit; M = Cu, Ni, Zn.In Table 2 and Table 3, the appearance of Pd-O coordination and the absence of Pd-Zr coordination in SNDP-Pd@HEAA, as opposed to As-SNDP-Pd@HEAA, suggested that the coordination environment was influenced by the introduction of oxygen during the preparation process. Such differences were more clearly distinguished from the wavelet transforms for k2-weighted EXAFS signals, as shown in FIG. 7.

[0099] In contrast to the significant oxidation observed in o-Pd (Table 4), the limited presence of Pd-O coordination in SNDP-Pd@HEAA, along with the simultaneous decrease in the intensities of white lines in the X-ray absorption near-edge structure spectrum compared to the PdO standard, further illustrated the minimal oxidation of Pd due to the high degree of Pd-M coordination, which reduced the likelihood of Pd oxidation.

[0100] The Pd-Pd interatomic distance of SNDP-Pd@HEAA was approximately 2.68 Å, which was slight shorter than that of As-SNDP-Pd@HEAA (approximately 2.75 Å) and Pd foil (approximately 2.74 A). Furthermore, both SNDP-Pd@HEAA and As-SNDP-Pd@HEAA exhibited lower total coordination numbers compared to Pd foil, suggesting that crystalline Pd existed in the form of small nanoparticles with a significant presence on surfaces. This observation further indicated the extensive interfaces within the distinctive SNDP structure.TABLE 4EXAFS fitting parameters at the Pd K-edge for o-Pd (S02 = 0.82)ShellCNR (Å)σ2ΔE0R factorPd foilPd-Pd122.74 ± 0.010.00557.1 ± 0.40.0041PdOPd-O3.8 ± 0.22.02 ± 0.010.00142.8 ± 1.10.0038Pd-Pd4.6 ± 0.33.06 ± 0.010.0033Pd-Pd14.5 ± 0.43.46 ± 0.010.0020o-PdPd-O2.6 ± 0.42.00 ± 0.010.00303.6 ± 1.50.0078Pd-Pd6.2 ± 0.72.77 ± 0.020.0167Pd-Pd14.9 ± 0.83.02 ± 0.010.0090Pd- Pd21.3 ± 0.23.41 ± 0.010.0011CN: coordination number; R: bond distance; σ2: Debye-Waller factor; ΔE0: inner potential correction; R factor: goodness of fit.

[0101] Additionally, all of the series of SNDP-M@HEAA materials (M=Ir, Pt, Ru, Au, Ag, or W) had similar X-ray diffraction patterns (FIG. 8A) and crystal amorphous dual-phase structures (FIG. 8B), demonstrating the universality of the method of the present invention.Example 4—Mechanisms of the HER Process

[0102] Further investigation was conducted on SNDP-Pd@HEAA as a model material to elucidate the structural advantages and mechanisms involved in the HER process.

[0103] FIGS. 9A-9B showed the electrocatalytic HER properties of the SNDP-Pd@HEAA samples. The linear sweep voltammogram curves showed that SNDP-Pd@HEAA had the highest HER performance with a low overpotential of 10.16 mV vs RHE at 10 mA cm−2, which was far superior to that of commercial 20 wt % Pt / C (34.01 mV vs RHE) and the other samples (i.e., As-SNDP-Pd@HEAA, o-Pd, As-Pd, o-HEAA, and As-HEAA).

[0104] Furthermore, the HER mechanisms for these catalysts were analysed using corresponding Tafel plots. Referring to FIGS. 10A-10B, the SNDP-Pd@HEAA catalyst exhibited the smallest Tafel slope of 30.4 mV decade−1 in the linear region, suggesting the fastest Heyrovsky-dominated Volmer-Tafel reaction mechanism during hydrogen evolution. The SNDP-Pd@HEAA samples with varying oxygen contents also displayed a similar trend.

[0105] It is well established that low charge transfer resistance indicates a superior electrocatalyst. Therefore, electrochemical impedance spectroscopy was conducted at an overpotential of 100 mV to gather data and confirm the occurrence of HER. As shown in FIG. 11, SNDP-Pd@HEAA had a much smaller diameter of the semicircular trend than the control samples, comparable to that of the carbon-containing 20 wt % Pt / C, suggesting that the unique SNDP structure in SNDP-Pd@HEAA had great potential for the optimisation of the corresponding electronic structure.

[0106] Since variations in surface area can impact HER performance, the electrochemical surface areas of the catalysts were estimated by measuring the electrochemical double-layer capacitance (Cdl) via cyclic voltammetry, representing the electrochemically active surface area (FIG. 12A). As shown in FIG. 12B, the calculated Cdl of SNDP-Pd@HEAA was 126.7 mF cm−2 and much higher than that of commercial 20 wt % Pt / C (46.0 mF cm−2), As-SNDP-Pd@HEAA (40.0 mF cm−2), and the other samples (all less than 8 mF cm−2).

[0107] As illustrated in FIG. 13A, the SNDP-Pd@HEAA electrocatalysts, both with and without the addition of O, exhibited an intrinsic dual-phase structure comprising crystalline and amorphous regions. Initially, three types of models were constructed-crystalline, amorphous, and crystalline / amorphous interface with and without the inclusion of oxygen. These models were subsequently optimized for structural integrity.

[0108] First, the adsorption energy of H2O molecules at different catalytic sites (ΔEH2O ) in the three models were calculated for the initial water adsorption step. FIGS. 13B-13C showed that the Ti, Zr, and Al sites had strong H2O adsorption in all three models, highlighting the major contribution of HEAA to ΔEH2O for the catalysts of the present invention. Notably, the increase in H2O adsorption resulting from the addition of elemental oxygen was most pronounced at the crystalline / amorphous interface.

[0109] FIG. 14 showed the atomic configurations and the corresponding electron density difference with bonding distance between the O atom in the H2O molecule and the active sites indexed after H2O adsorption at representative Pd, Ti, Zr, and Al sites in the interface models with and without elemental O. The shortening of the bonding distance between the active sites and the O atom in the H2O molecule and a left shift away from the Fermi level (EF) in the p-orbitals partial density of states (p-PDOS) of the O atom in H2O molecule (FIG. 15) revealed the physical origin of the increase in ΔEH2O due to the elemental O.

[0110] It is well known that the Gibbs free energy of H* (ΔGH*) is a key descriptor of the HER performance. A value close to zero is preferred because the HER process includes the reversible adsorption and desorption of H*, which require the interaction between catalytic sites and H* to be neither too strong nor too weak. The easier introduction of oxygen into the amorphous region resulted in less oxygen being able to coordinate directly with the active Pd centre in the crystal region.

[0111] To specify the effect of O coordination, ΔGH* values of Pd sites were compared under three conditions: 1) without O coordination, 2) with the nearest O coordination, and 3) with the next-nearest O coordination. The observation revealed that nearest O coordination negatively affected ΔGH*, whereas next-nearest O coordination proved advantageous for optimizing ΔGH*.

[0112] Calculations based on density-functional theory (DFT) were conducted to explore the atomistic physical origin of the superior HER performance of the SNDP-Pd@HEAA of the present invention. The variation in ΔGH* depicted in FIG. 16A, along with the corresponding atomic arrangements illustrated in FIGS. 16B-16C, were analyzed following the adsorption of H protons onto Pd sites situated on the catalyst surfaces of the crystal, amorphous, and crystalline / amorphous interface models. The results showed that Pd sites at the crystalline / amorphous interface had more favourable ΔGH* values than those in the crystal and amorphous models. Specifically, the Pd site with the next-nearest O coordination had a near-zero ΔGH* of 0.062 eV, indicating the positive effect of the next-nearest O coordination on the HER performance. The high content of O in the amorphous phase and the high content of Pd in the crystalline phase may lead to a high proportion of Pd sites with next-nearest O coordination.

[0113] Furthermore, the effects of the nearest and next-nearest O coordination at the Pd sites of crystalline / amorphous interface models were examined by analysing the two-dimensional electron density difference (illustrated in FIG. 17A, where Ti coordination was selected as a representative for ‘Interface’ and ‘Interface-O-NN’ models) and the d-orbital partial density of states (d-PDOS) (FIG. 17B). The observation revealed that the Pd site experienced the most significant electron loss and a leftward shift of the d-band center away from the Fermi level due to the nearest O coordination, exacerbating the HER performance. Meanwhile, the electron loss of Pd was weakened, and there was a right shift of the d-band centre toward the Fermi level when the Pd site was next-nearest neighbouring with the O atom, which effectively promoted the electron transfer and increased the strength of the interaction between H* and the Pd sites and thus optimised ΔGH*.

[0114] Apart from the Pd sites, favorable values of ΔGH* were also observed at monatomic catalytic sites, such as Pd-Al and Pd-Cu sites. This observation indicated that the synergistic effect between Pd sites and HEAA significantly contributed to the outstanding HER performance of the developed electrocatalyst (FIGS. 18A-18B), rendering the HER performance of the crystalline / amorphous dual-phase catalyst without elemental O comparable to that of commercial Pt / C.

[0115] Overall, the experiments and DFT revealed that a large number of the next-nearest O coordinated active sites at interfaces gave rise to a near-zero value of ΔGH* and strong H2O and hydrogen / proton adsorption. The promotion of H2O adsorption and hydrogen / proton adsorption contributed to the excellent HER performance of SNDP-Pd@HEAA. The next-nearest O coordination with Pd sites effectively promotes the electron transfer ability and increases the strength of interaction between H* and the Pd sites and thus optimises ΔGH* and yields excellent HER performance.Example 5—Effect of Introducing Oxygen

[0116] The introduction of oxygen may lower the overpotential and accelerated the reaction kinetics. FIGS. 19A-19C summarized the relationship between the oxygen content and the electrocatalytic performance. All SNDP-Pd@HEAA samples with varying oxygen content exhibited an electrochemically active surface area that was significantly greater than or comparable to that of 20 wt % Pt / C. This highlighted the importance of the crystal-amorphous dual-phase structure and the addition of oxygen. The results showed that the SNDP-Pd@HEAA with an O concentration of 42.24 at. % had the best electrocatalytic performance. This could be attributed to the introduction of oxygen, which weakened the adsorption energy of OH* due to a downshifted d-band center of Pd, resulting in lower impedance and a larger electrochemical surface area. However, an excessively high oxygen concentration led to severe oxidation of the metal components, as indicated by an upshifted d-band center of Pd, higher impedance, and a smaller electrochemical surface area. Therefore, the enhancement in HER performance resulting from the addition of oxygen could primarily be attributed to the optimized electronic coupling and increased surface area within the SNDP-Pd@HEAA samples.

[0117] In FIG. 20, the overpotentials at a current density of 10 mA cm−2 for previously reported HER electrocatalysts tested in alkaline media were compared. The SNDP-Pd@HEAA catalyst was shown to be competitive with the state-of-the-art HER catalysts. In particular, Table 5 listed the hydrogen evolution reaction performance of SNDP-Pd@HEAA in 1 M KOH and previously reported crystal-amorphous dual-phase catalysts.TABLE 5OverpotentialTafel slopeElectrocatalysts(at 10 mA cm−2)(mV dec−1)NoteSNDP-Pd@HEAA10.1638.9This workAs-SNDP-Pd@HEAA53.353.3This workAlMnRu23.7 / Pt-a / c-CoNiHPi1949.2Prior artCoP / MnOx13559.4

[0118] Apart from enhancing catalytic efficiency, the impact of introducing oxygen on stability was also examined. Referring to FIG. 21A, SNDP-Pd@HEAA exhibited good stability during a 100-h long-term test at a current density of 20 mA cm−2, with the overpotential of SNDP-Pd@HEAA decreasing by only approximately 17.3 mV, which was much smaller than the decrease for As-SNDP-Pd@HEAA. Following the 100-hour long-term test, the SNDP-Pd@HEAA maintained its SNDP structure and valence states, confirming the robust stability of SNDP-Pd@HEAA during HER operation. Nevertheless, at the end of the stability test, the elemental Al, Zn, Ti, Zr, and Si in As-SNDP-Pd@HEAA were noticeably oxidized (FIG. 21B), suggesting that the introduction of oxygen effectively enhanced the structural stability of SNDP-Pd@HEAA.

[0119] The concentrations of elemental Pd, Al, Zn, Ti, Zr, Si, Cu, and Ni dissolved in solution were measured at the conclusion of a 200-hour durability test under alkaline conditions, conducted at a current density of 200 mA cm−2, using inductively coupled plasma-optical emission spectrometry, as listed in Table 6.TABLE 6ICP-OES results for SNDP-Pd@HEAA after 200h at current density of 200 mA cm−2ConcentrationLimit of reporting(mmol / L)(mmol / L)Pd0.00200.00041Al0.00260.00104Zn0.00170.00009Ti0.00120.00008Zr0.00050.000078Si0.43210.0020Cu0.00230.00015Ni0.00390.00026O / / *The lowest concentration of a substance that can be reliably measured by ICP-OES.

[0120] The concentrations of all detected elements were near the detection limit of the instrumentation, consistent with the slight change observed in the XPS elemental composition analysis of SNDP-Pd@HEAA. This further highlighted the superior stability of SNDP-Pd@HEAA.

[0121] Moreover, as shown in FIGS. 22A-22F, the introduction of oxygen to the SNDP catalysts led to electrocatalytic HER and / or oxygen evolution reaction (OER) performances that surpassed those of the other samples. This further underscored the universality of oxygen addition as an effective strategy for enhancing electrocatalytic performance.Example 6—Preparation of flow-Type Membrane Exchange Assembly Alkaline Water Electrocatalysis Cell

[0122] The SNDP-Pd@HEAA deposited on carbon felt and SNDP-Ir@HEAA deposited on a porous titanium sheet were respectively used as the cathode and anode.

[0123] Referring to FIG. 23, it was observed that the SNDP-Pd@HEAAISNDP-Ir@HEAA electrolyser operated steadily for 1000 hours at 500 mA cm−2, with no significant reduction in voltage relative to the initial state.

[0124] The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

[0125] The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated.DEFINITIONS

[0126] Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and / or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the present invention.

[0127] Furthermore, throughout the specification and claims, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0128] As used herein and not otherwise defined, the terms “substantially,”“substantial,”“approximately” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can encompass instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0129] References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0130] In the methods of preparation described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E, and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps can also be repeated. Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately.

[0131] The term “double layer capacitance” refers to the capacitance effect formed between the electrode surface and the electrolyte solution, where the separation of charges between the adsorbed charges on the electrode surface and the corresponding ions in the electrolyte creates a charge barrier. This charge barrier can store charge and produce a capacitance effect under the influence of an electric field.

[0132] The term “at. %” stands for atomic percent. It is a unit of concentration used in chemistry and materials science to express the proportion of one type of atom relative to the total number of atoms in a mixture, compound, or alloy. For example, in a sample with 10 at. % of element A and 90 at. % of element B, it means that out of every 100 atoms in the sample, 10 are atoms of element A and 90 are atoms of element B.

[0133] Other definitions for selected terms used herein may be found within the detailed description of the present invention and apply throughout. Unless otherwise defined, all other technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the present invention belongs.

Examples

example

Example 1—Materials and Methods

Materials

[0073]Raw element granules of aluminium (Al), zinc (Zn), titanium (Ti), zirconium (Zr), silicon (Si), copper (Cu), and nickel (Ni) with a purity higher than 99.95% were mixed by China Material Technology Co., Ltd to achieve the high-entropy amorphous alloy (HEAA) sputtering target with a theoretical atomic composition (at %) of Al0.5ZnTiZrSiCuNi. The pure palladium (Pd) target with a purity higher than 99.99% was purchased from Angstrom Engineering Inc. Co., Ltd. Analytical grade potassium hydroxide (KOH), and absolute ethanol were supplied by Sigma Aldrich. All of the solutions were prepared with Milli-Q water (18.2 MΩcm).

Material Characterization

[0074]The samples were characterised through scanning electron microscopy (SEM, Philips XL-30 FESEM), atomic force microscopy (AFM, Bruker Icon), and high-resolution transmission electron microscopy (TEM, JEOL TEM 2100F FEG operated with an accelerating voltage of 200 kV). Atomic-resolution scanning ...

example 2

Preparation of SNDP-Pd@HEAA Catalysts

The catalyst with novel supra-nano dual-phase structure was synthesized by introducing a large amount of oxygen innovatively. In this example, SNDP-Pd@HEAA catalysts were synthesized using double-target magnetron sputtering, a bottom-up, industrialized method that enables the large-scale production of a wide variety of nanomaterials. The fabrication method used in this work was magnetron co-sputtering (Angstrom Engineering Inc. Co., Ltd). The background vacuum was 4×10−7 Torr. HEAA and Pd targets were used for co-sputtering. The SNDP-Pd@HEAA was then deposited on different substrates (Si(001), carbon cloth, and nickel foam, Pt foil) simultaneously for different purposes.

[0086]The thickness of the films was easily controlled by the sputtering time and the composition of the films was controlled by tuning the difference in substrate-to-target distances. During co-sputtering process, the power supplied to the HEAA target with a direct-current source...

example 3

Characterization of the SNDP-Pd@HEAA Catalysts

[0088]Referring to FIG. 1A, the X-ray diffraction patterns of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA catalysts had a broad diffraction peak without strong Bragg crystalline diffraction. This peak was much narrower than the diffraction peak of the amorphous HEAA, indicating the amorphous and ultra-small nanocrystalline nature of the catalysts. The SEM images of SNDP-Pd@HEAA deposited on carbon cloth revealed a smooth surface (FIG. 1B). Additionally, atomic force microscopy revealed the ultra-smooth surface of SNDP-Pd@HEAA, exhibiting a roughness of only approximately 1.36 nm (FIG. 1C).

[0089]The components of SNDP-Pd@HEAA were identified through EDS mapping. Referring to FIG. 1D, the SNDP-Pd@HEAA contained 25.12 at % Pd, 42.24 at % O , 2.74 at % Al, 3.35 at % Si, 2.9 at % Ti, 3.99 at % Ni, 4.62 at % Cu, 8.62 at % Zn, and 6.41 at % Zr.

[0090]The TEM image of FIG. 2A showed a homogeneous distribution of nanoparticles surrounded by a thin amorphous ...

FIELD OF THE INVENTION

[0001] The present invention generally relates to the fields of electrochemical catalytic materials. More particularly, it relates to an oxygen-dominated supra-nanostructure that offers a pathway to developing an electrocatalyst with exceptionally high activity for hydrogen evolution.BACKGROUND OF THE INVENTION

[0002] The electrochemical splitting of water to produce hydrogen is widely considered as an ideal strategy to decrease the consumption of traditional fossil fuels and be beneficial to the carbon neutral. Especially, the hydrogen evolution reduction (HER) is a crucial reaction involved in electrochemical splitting. In recent years, there have been continuous efforts to develop high-performance electrocatalytic materials for the HER by carefully manipulating their structure or morphology.

[0003] Currently, the commercial HER catalysts used for water splitting are based on Pt nanoparticles dispersed on a carbon substrate, e.g., 20% Pt / C. Moreover, the fabricate method of the current commercial Pt / C is complex and at very high cost. Even though the HER performance of commercial Pt / C satisfies the needs of water splitting, it is desirable to further develop a new catalyst with small overpotential, high electrical conductivity, and high stability, which can further decrease the use of energy.

[0004] Crystal-amorphous supra-nano dual-phase (SNDP) materials are a novel type of nanostructure characterized by a homogeneous and continuous distribution of both crystalline and amorphous regions, with the crystal size and the thickness of the amorphous regions being less than 10 nm. SNDP materials inherit the advantages of both crystalline and amorphous phases and are a prospective alternative to commercial Pt / C HER catalysts, owing to their multicomponent synergetic effect and tremendously large active catalytic interfaces. In addition, SNDP materials with coexisting phases in close contact that differ in terms of their chemical nature have unique interfacial interactions. Such characteristics of SNDP materials fulfil the requirements of superior electrocatalysts.

[0005] Oxygen is an essential component of many materials, with the presence or absence of oxygen affecting material performance. Highly electronegative oxygen affects the local coordination environment of an active site and thus shifts the active site to a higher oxidized state and affects the water absorption ability and Gibbs free energies (ΔGH*) of adsorbed hydrogen (H*).

[0006] In a catalytic reduction process for the HER, it is undesirable for the active center to coordinate directly with oxygen. Therefore, using oxygen to manipulate the electronic structure to enhance hydrogen evolution presents a significant challenge.SUMMARY OF THE INVENTION

[0007] Accordingly, the present invention presents a series of SNDP materials prepared through industrialized magnetron sputtering between a high-entropy amorphous alloy (HEAA) target, Al0.5ZnTiZrSiCuNi, and transition metal targets, specifically Pd, Ir, Pt, Ru, Au, Ag, V, and W. The composition of the SNDP structure can be precisely controlled over a wide range by altering the O content.

[0008] In particular, in a first aspect, the present invention provides an oxygen-dominated supra-nano dual-phase catalytic reaction material on a substrate, which includes a uniform oxygen-enriched amorphous shell and a core encapsulated within the uniform oxygen-enriched amorphous shell. The oxygen-dominated supra-nano dual-phase catalytic reaction material has an intrinsic crystal-amorphous dual-phased structure. The oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10 to 25 mV vs RHE at 10 mA cm−2.

[0009] The crystal phase has a face-centred cubic structure and the amorphous phase has a typical diffused-ring structure.

[0010] In one embodiment, the uniform oxygen-enriched amorphous shell is made from a high-entropy amorphous alloy including AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy. The uniform oxygen-enriched amorphous shell has a thickness of approximately 1-5 nm.

[0011] In one embodiment, the core is made from at least one transition metal including palladium, platinum, iridium, ruthenium, rhodium, gold, silver, or non-noble metal of vanadium, molybdenum, tungsten, and even NiMo, NiW binary alloy. The core is 1-10 nm in diameter.

[0012] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 20-30 at % of Pd, 10-50 at % of O, 1-5 at % of Al, 5-20 at % of Si, 5-20 at % of Ti, 5-20 at % of Ni, 5-20 at % of Cu, 1-15 at % of Zn, and 5-20 at % of Zr.

[0013] In another embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains10-30 at % of Pt, 10-40 at % of O, 5-20 at % of Fe, 5-20 at % of Co, 5-20 at % of Ni, 1-15 at % of Mo, 1-10 at % of P, and 1-10 at % of B.

[0014] In one embodiment, the substrate includes nickel foam, carbon cloth, carbon paper, silicon wafer, porous titanium sheet, titanium foam, or platinum foil.

[0015] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material demonstrates a stability in a 100-hour long-term test at a current density of 20 mA cm−2 in a three-electrode system and can operate steadily for 1000 h at a current density of 500 mA cm−2 in a flow-type membrane exchange assembly alkaline water electrocatalysis cell.

[0016] In another aspect, the oxygen-dominated supra-nano dual-phase catalytic reaction material can used to make a water splitting electrode, including HER electrode and OER electrode.

[0017] In another aspect, the present invention provides a method for fabricating an oxygen-dominated supra-nano dual-phase catalytic reaction material, including co-sputtering a crystal metal target and a high-entropy amorphous alloy target on a substrate by industrial magnetron sputtering, and wherein oxygen gas is introduced during the magnetron sputtering process.

[0018] In one embodiment, the oxygen gas has a flow velocity ranging from approximately 0.01 sccm to 50 sccm.

[0019] In one embodiment, the high-entropy amorphous alloy target is a multi-component alloy comprising AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy.

[0020] In one embodiment, the industrial magnetron sputtering adopts a sputtering temperature at approximately 0.1 to 200° C.

[0021] In one embodiment, the substrate has a rotation speed in the range from 0.1 rpm to 20 rpm during sputtering.

[0022] The present invention provides new SNDP materials based on a transition metal with high-entropy amorphous alloy via industrial magnetron sputtering at ambient temperature by adopting an O domination strategy. The SNDP palladium / high-entropy amorphous alloy (SNDP-Pd@HEAA) of the present invention includes Pd-rich nanocrystalline cores and O-rich amorphous glassy shells, enriched with plenty of next-nearest O coordinated active Pd sites, which actively accelerates hydrogen proton adsorption / desorption, exhibits near zero overpotential (10.16 mV, which is much lower than that of 34.01 mV of commercial 20% Pt / C) at 10 mA cm−2 and superior stability for hydrogen evolution under alkaline conditions. This SNPD nanostructure production and composition manipulation technique, and the next-nearest O coordinated active sites mechanism, establishes a new paradigm for hydrogen evolution reaction catalysts.

[0023] The catalysts of the present invention offer the following advantages: (1) They demonstrate lower overpotential and high stability for hydrogen evolution reaction compared to the existing commercial 20 wt % Pt / C catalysts; (2) By altering the oxygen concentration, the composition of the SNDP structure is precisely regulated over a wide range, overcoming the restricted diversity and constricted compositional regulation range of conventional SNDP structures; and (3) This invention utilizes room-temperature industrial magnetron sputtering technology, which, compared to the techniques used in existing catalysts, has a greater potential for large-scale production.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention are described in more details hereinafter with reference to the drawings, in which:

[0025] FIG. 1A depicts XRD patterns of supra-nano dual-phase palladium / high-entropy amorphous alloy, including SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, o-HEAA, As-HEAA, o-Pd, and As-Pd. FIG. 1B shows scanning electron microscopy of SNDP-Pd@HEAA on carbon cloth. FIG. 1C shows atomic force microscopy of SNDP-Pd@HEAA. FIG. 1D shows SEM energy-dispersive spectroscopy (EDS) mapping of SNDP-Pd@HEAA;

[0026] FIG. 2A shows low-magnification transmission electron microscopy of SNDP-Pd@HEAA. FIG. 2B shows a cross-sectional high-resolution transmission electron microscopy (TEM) image of SNDP-Pd@HEAA. The fast Fourier transformation images in the insets show that the crystal phase has a face-centred cubic structure and the amorphous phase has a typical diffused-ring structure. FIG. 2C depicts the corresponding selected area electron diffraction pattern of SNDP-Pd@HEAA in FIG. 2A;

[0027] FIG. 3A shows three-dimensional reconstructed TEM image of SNDP-Pd@HEAA. FIG. 3B depicts grain-size distribution obtained from multiple TEM images. The plan view is for the x-z plane, and cross-section 1 and cross-section 2 correspond to the x-y plane and y-z plane, respectively. FIG. 3C shows a typical high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image. The arrow shows the direction of the line scan of the energy-dispersive spectroscopy. FIG. 3D depicts line scan intensity of elements in the energy-dispersive spectroscopy along the direction indicated by the arrow in FIG. 3C. FIG. 3E shows three-dimensional atom probe tomography images showing the elemental distribution and multicomponent nature;

[0028] FIG. 4A shows TEM images of SNDP-Pd@HEAA with different O contents. FIG. 4B depicts XRD patterns of SNDP-Pd@HEAA with different O contents;

[0029] FIG. 5A depicts Pd 3d X-ray photoelectron spectroscopy of SNDP-Pd@HEAA. FIG. 5B depicts O 1s X-ray photoelectron spectroscopy of SNDP-Pd@HEAA. FIG. 5C depicts X-ray photoelectron microscopy of SNDP-Pd@HEAA with detailed fitting peaks;

[0030] FIG. 6A depicts Pd K-edge X-ray absorption near-edge structure spectra of SNDP-Pd@HEAA. FIG. 6B depicts corresponding k2-weighted Fourier transform of the X-ray absorption fine structure (EXAFS) spectra. FIG. 6C depicts fitting of the k2-weighted Fourier transform of EXAFS spectra at the Pd K-edge of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA;

[0031] FIG. 7 depicts wavelet transforms for k2-weighted EXAFS signals at the Pd K-edge of SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, Pd foil and PdO;

[0032] FIG. 8A depicts XRD patterns of SNDP-M@HEAA samples (M=Au, Ag, W, Pt, Ru, Ir, Pd). FIG. 8B shows TEM images of SNDP-M@HEAA samples;

[0033] FIG. 9A depicts polarisation curves of samples deposited on glassy carbon obtained at a scan rate of 5 mV s−1 with iR correction, and FIG. 9B polarisation curves of the SNDP-Pd@HEAA samples with different O contents in 1 M KOH with iR correction;

[0034] FIG. 10A depicts corresponding Tafel plots of FIG. 9A. FIG. 10B depicts corresponding Tafel plots of FIG. 9B;

[0035] FIG. 11 depicts electrochemical impedance spectroscopy of SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, o-Pd, As-Pd, o-HEAA, As-HEAA, and 20% Pt / C at an overpotential of 100 mV in 1 M KOH solution at room temperature;

[0036] FIG. 12A depicts cyclic voltammograms in the region of 0-0.1 V vs. RHE at various scan rates for SNDP-Pd@HEAA, As-SNDP-Pd@HEAA, o-Pd, As-Pd, o-HEAA, As-HEAA, 20% Pt / C. FIG. 12B depicts calculated electrochemical double-layer capacitance for the as-prepared materials;

[0037] FIG. 13A shows structural configurations of SNDP models without and with O. FIG. 13B depicts DFT-calculated ΔEH2O of H2O molecules at various sites in the interface models with and without O element. For reference, ΔEH2O of the Pt(111) surface is marked by a grey dashed line. FIG. 13C depicts DFT calculation of ΔEH2O of H2O molecules at Pd sites in crystal, amorphous, and interface models with and without elemental O. For reference, ΔEH2O of the Pt(111) surface is marked by a grey dashed line;

[0038] FIG. 14 depicts DFT simulations of atomic configurations and the corresponding electron density difference after H2O adsorption at Pd, Ti, Zr, and Al sites in the interface models with and without elemental O. dx-o represents the bonding distances between the O atom at the H2O and Pd, Ti, Zr, and Al sites;

[0039] FIG. 15 depicts p-PDOS of the O atom in an H2O molecule after H2O adsorption onto Pd, Ti, Zr, and Al sites in the interface models with and without elemental O, respectively. The black dashed lines at zero energy indicate the Fermi level (EF);

[0040] FIG. 16A depicts representative local chemical environment after H* adsorption at Pd top sites in crystalline / amorphous interface models without O coordination, with nearest O coordination, and with next-nearest O coordination. FIG. 16B depicts ΔGH* profiles for Pd sites in the crystal, amorphous, and crystalline / amorphous interface models without O coordination, with nearest O coordination, and with next-nearest O coordination, respectively. FIG. 16C depicts local chemical environment after H* adsorption at Pd top sites in the crystal and amorphous models without O coordination, with nearest O coordination, and with next-nearest O coordination;

[0041] FIG. 17A depicts DFT simulation results of the two-dimensional electron density difference and equilibrium distance for Pd-Ti, Pd-O, and Pd-Ti (O). FIG. 17B depicts d-orbital partial density of states (d-PDOS) of Pd catalytic sites at the interface without O coordination, with nearest O coordination, and with next-nearest O coordination. The black dashed line indicates the Fermi level. The solid straight lines indicate the corresponding d-band centres;

[0042] FIG. 18A depicts Gibbs free energy (ΔGH*) profiles for various bridge and hollow sites in crystalline / amorphous interface models without elemental O and with elemental O. FIG. 18B depicts local chemical environment of various H* adsorption sites (bridge and hollow) in crystalline / amorphous interface models without and with elemental O;

[0043] FIG. 19A depicts relationship between the catalytic performance and the O content of SNDP-Pd@HEAA, showing an improvement in the hydrogen evolution reaction performance as the oxygen content increases. FIG. 19B depicts electrochemical impedance spectroscopy of SNDP-Pd@HEAA samples with different O contents in 1 M KOH solution at an overpotential of 100 mV and room temperature. FIG. 19C depicts cyclic voltammograms in the region of 0-0.1 V vs. RHE at various scan rates for SNDP-Pd@HEAA samples with different oxygen atomic contents;

[0044] FIG. 20 depicts performance comparison of catalysts at the current density of 10 mA cm−2 in alkaline solutions;

[0045] FIG. 21A depicts long-time performances of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA at a constant current density of 20 mA cm−2 in alkaline solutions. FIG. 21B depicts X-ray photoelectron microscopy of As-SNDP-Pd@HEAA after 100 h in 1 M KOH;

[0046] FIG. 22A depicts polarisation curves of SNDP-Pt@HEAA and As-SNDP-Pt@HEAA in 1 M KOH with iR correction. FIG. 22B depicts polarisation curves of SNDP-Au@HEAA and As-SNDP-Au@HEAA in 1 M KOH with iR correction. FIG. 22C depicts polarisation curves of SNDP-Ag@HEAA and As-SNDP-Ag@HEAA in 1 M KOH with iR correction. FIG. 22D depicts polarisation curves of SNDP-W@HEAA and As-SNDP-W@HEAA in 1 M KOH with iR correction. FIG. 22E depicts polarisation curves of SNDP-Ir@HEAA, As-SNDP-Ir@HEAA, and IrO2 in 1 M KOH with iR correction. FIG. 22F depicts polarisation curves of SNDP-Ru@HEAA and As-SNDP-Ru@HEAA in 1 M KOH with iR correction; and

[0047] FIG. 23 depicts long-term durability of the SNDP-Pd@HEAA / SNDP-Ir@HEAA cell at a constant current density of 0.5 A cm−2.DETAILED DESCRIPTION

[0048] Fabricating excellent hydrogen evolution reaction catalysts with near-zero overpotential at a large scale is challenging. The supra-nano dual-phase (SNDP) structure, which incorporates the optimal benefits of both crystalline and amorphous phases with a multicomponent synergy effect and enormously large active catalytic inter-phases, is a promising commercial platinum on carbon (Pt / C) alternative. However, a restricted variety of elements are readily available for fabricating SNDP structures and the compositional regulation of them is limited.

[0049] Accordingly, the present invention provides an oxygen-dominated supra-nano dual-phase catalytic reaction material on a substrate, which includes a uniform oxygen-enriched amorphous shell and a core encapsulated within the uniform oxygen-enriched amorphous shell. The oxygen-dominated supra-nano dual-phase catalytic reaction material has an intrinsic crystal-amorphous dual-phased structure. The oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10 to 25 mV vs RHE at 10 mA cm−2.

[0050] Preferably, the oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10.16 mV vs RHE at 10 mA cm−2.

[0051] In one embodiment, the uniform oxygen-enriched amorphous shell is made from a high-entropy amorphous alloy including AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy. The uniform oxygen-enriched amorphous shell has a thickness of approximately 1-5 nm.

[0052] In one embodiment, the core is made from at least one transition metal including palladium, platinum, iridium, ruthenium, rhodium, gold, silver, or non-noble metal of vanadium, molybdenum, tungsten, and even NiMo, NiW binary alloy. The core is 1-10 nm in diameter.

[0053] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 20-30 at % of Pd, 10-50 at % of O, 1-5 at % of Al, 5-20 at % of Si, 5-20 at % of Ti, 5-20 at % of Ni, 5-20 at % of Cu, 1-15 at % of Zn, and 5-20 at % of Zr.

[0054] Preferably, O concentration of 42.24 at. % had the best electrocatalytic performance. The oxygen-dominated supra-nano dual-phase catalytic reaction material contains 25.12 at % of Pd, 42.24 at % of O, 2.74 at % of Al, 3.35 at % of Si, 2.9 at % of Ti, 3.99 at % of Ni, 4.62 at % of Cu, 8.62 at % of Zn, and 6.41 at % of Zr.

[0055] In another embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 10-30 at % of Pt, 10-40 at % of O, 5-20 at % of Fe, 5-20 at % of Co, 5-20 at % of Ni, 1-15 at % of Mo, 1-10 at % of P, and 1-10 at % of B.

[0056] In one embodiment, the substrate includes nickel foam, carbon cloth, carbon paper, silicon wafer, porous titanium sheet, titanium foam, or platinum foil.

[0057] In one embodiment, the oxygen-dominated supra-nano dual-phase catalytic reaction material demonstrates a stability in a 100-hour long-term test at a current density of 20 mA cm−2 in a three-electrode system and can operate steadily for 1000 h at a current density of 500 mA cm−2 in a flow-type membrane exchange assembly alkaline water electrocatalysis cell.

[0058] The intriguing crystal / amorphous dual-phase structure and large number of next-nearest O coordinated active sites at interfaces give rise to a near-zero value of ΔGH* and a strong H2O adsorption capability that promote H2O adsorption and hydrogen / proton adsorption and thus contribute to the excellent HER performance of SNDP-Pd@HEAA.

[0059] The crystal region is enriched with the crystal target's elements, while the amorphous region is highly enriched with oxygen. All elements from the target are uniformly distributed within the material. The content of the crystal target's elements in the crystal region is higher than in the amorphous region. The atomic ratio of the crystal target's elements ranges from approximately 20 at % to 80 at % in the crystal region and from approximately 0 at % to 40 at % in the amorphous region. The atomic ratio of oxygen ranges from approximately 0.01 at % to 30 at % in the crystal region and from approximately 10 at % to 70 at % in the amorphous region. The atomic ratio of all elements from the target ranges from approximately 0.01 at % to 30 at %.

[0060] In one embodiment, the oxygen content of the crystal region is much lower than that in the amorphous region.

[0061] SNDP-Pd@HEAA has a homogeneously distributed three-dimensional structure that comprises a Pd-rich crystalline core with a diameter of approximately 1-10 nm and an HEAA-enriched homogeneous amorphous shell with a thickness of approximately 1-5 nm.

[0062] In one embodiment, the SNDP material is SNDP palladium / high-entropy amorphous alloy (SNDP-Pd@HEAA). The SNDP-Pd@HEAA, with Pd-rich grains (4.76 nm in diameter) and uniform O-enriched amorphous shells (thickness of approximately 1.2 nm), exhibited a near-zero overpotential (10.16 mV at 10 mA cm−2) and is thus a prospective alternative to commercial Pt / C HER catalysts under alkaline conditions.

[0063] The size of the nanograins and the thickness of the amorphous layer in the catalyst can be easily adjustable by simply applying different power to the targets and the rotation speed of the receiving substrate during the magnetron sputtering process. For instance, the power source applied to the metal target is radio-frequency (RF) power supply. The power source applied to the high-entropy amorphous alloy target is direct-current (DC) power supply. The RF power supply is in the range from 30 to 200 W, and power of the DC power supply is in the range from 35 to 225 W.

[0064] When directly used as an HER electrocatalyst without further post-treatment, SNDP-Pd@HEAA has an overpotential close to zero (10.16 mV at 10 mA cm−2) under alkaline conditions. The long-term durability of SNDP-Pd@HEAA in alkaline media can be attributed to the restricted oxidation tendency of O-dominated HEAA.

[0065] In one embodiment, the SNDP structure can be deposited on various substrates based on its applications. For instance, the substrates may include nickel foam, carbon cloth, carbon paper, silicon wafer, titanium sheet, or platinum foil.

[0066] All SNDP samples deposited uniformly on the conductive substrate via magnetron sputtering exhibited similarly smooth surfaces. However, the electrochemically active surface area of SNDP-Pd@HEAA with flat and smooth surface, was 2.75 times greater than that of commercial 20 wt % Pt / C containing ultrasmall nanoparticles.

[0067] In another aspect, the oxygen-dominated supra-nano dual-phase catalytic reaction material can used to make a water splitting electrode.

[0068] In another aspect, the present invention also presents an industrialized method of developing SNDP nanostructures with near-zero potential for widespread electrocatalytic applications and new insight into next-nearest O coordinated active sites.

[0069] In particular, the present invention provides a method for fabricating an oxygen-dominated supra-nano dual-phase catalytic reaction material. The method includes co-sputtering a crystal metal target and a high-entropy amorphous alloy target on a substrate by industrial magnetron sputtering. Oxygen gas is introduced during the magnetron sputtering process.

[0070] The crystal metal target and the high-entropy amorphous alloy target can be combined arbitrarily according to the final application scenarios and operation condition. The application scenarios are hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, hydrogen oxidation reaction, carbon dioxide reduction reaction, water splitting, proton exchange membrane fuel cell materials and metal-air batteries. The operation condition can be in a wide range of pH value.

[0071] The high-entropy amorphous alloy target is multi-component alloy which is easy to form amorphous structure during the sputtering process, which need some easily oxidized elements and some non-metallic elements, such as AlZnTiZrSiCuNi-containing alloy.

[0072] The industrial magnetron sputtering adopts a sputtering temperature at approximately 0.1 to 200° C.EXAMPLEExample 1—Materials and MethodsMaterials

[0073] Raw element granules of aluminium (Al), zinc (Zn), titanium (Ti), zirconium (Zr), silicon (Si), copper (Cu), and nickel (Ni) with a purity higher than 99.95% were mixed by China Material Technology Co., Ltd to achieve the high-entropy amorphous alloy (HEAA) sputtering target with a theoretical atomic composition (at %) of Al0.5ZnTiZrSiCuNi. The pure palladium (Pd) target with a purity higher than 99.99% was purchased from Angstrom Engineering Inc. Co., Ltd. Analytical grade potassium hydroxide (KOH), and absolute ethanol were supplied by Sigma Aldrich. All of the solutions were prepared with Milli-Q water (18.2 MΩcm).Material Characterization

[0074] The samples were characterised through scanning electron microscopy (SEM, Philips XL-30 FESEM), atomic force microscopy (AFM, Bruker Icon), and high-resolution transmission electron microscopy (TEM, JEOL TEM 2100F FEG operated with an accelerating voltage of 200 kV). Atomic-resolution scanning transmission electron microscopy (STEM) images and energy-dispersive spectrometry (EDS) maps were acquired on a Titan FEI Themis G60-300 S / TEM (fitted with a high-brightness field emission gun (X-FEG), probe CS corrector, and super-X EDS with four windowless silicon drift detectors). X-ray diffraction (XRD) patterns were collected using an X-ray diffractometer (Rigaku SmartLab) with Cu Kα radiation (λ=1.5418 Å). Three-dimensional atomic probe tomography (APT) characterisation was performed using a local electrode atom probe (CAMECA LEAP 5000 XR). The APT experiments were conducted at 60 K in laser mode with a laser energy of 50 pJ and a pulse rate of 125 kHz, and the detection rate was 0.3%. The corresponding three-dimensional reconstructions and data analysis were performed using Imago Visualization and Analysis Software (IVAS, version 3.8.2). Both TEM and APT specimens were prepared on an FEI focused ion beam / scanning electron microscope (FIB / SEM) adopting the lift-out and annular milling method. In the preparation of stability-tested TEM and APT specimens, SNDP-Pd@HEAA was sputtered on nickel foam. The leached metallic ions in the stability test were measured through inductively coupled plasma-optical emission spectrometry (ICP-OES) (Optima ICP-OES Spectrometer, PerkinElmer) with a 10-times diluted solution. (The results were corrected with the dilution factor.) X-ray photoelectron microscopy was performed on an ESCALAB 250 photoelectron spectrometer (ThermoFisher Scientific) with Al Ka (1486.6 eV) as the X-ray source set at 150 W and a pass energy of 30 eV for high-resolution scanning. The base pressure was 3 ×10−9 mbar, and the binding energies were referenced to the C1s line at 284.8 eV from adventitious carbon. The X-ray absorption near edge structure and extended X-ray absorption fine structure experiments on the SNDP-Pd@HEAA catalysts were carried out at the BL14W1 beamline of the Shanghai Synchrotron Radiation Facility. The data were collected in fluorescence mode using a Lytle detector while the corresponding reference sample was measured in transmission mode. The incident beam was monochromatised using a Si(111) fixed-exit, double-crystal monochromator, and a harmonic rejection mirror was applied to cut off the high-order harmonics. The obtained X-ray absorption fine structure data were processed in Athena (version 0.9.26) for background, pre-edge line, and post-edge line calibrations. Fourier transformed fitting was then carried out in Artemis (version 0.9.26). Adopting a k3 weighting scheme, a k-range of 3-14 Å−1 and an R range of 1 to approximately 3 Å were used in the fitting for the Pd foil and a k-range of 3-11 Å−1 and an R range of 1 to approximately 3.5 Å were used in the fitting for the SNDP-Pd@HEAA samples. Three parameters, the coordination number, bond length, and E0 shift (CN, R, ΔE0), were freely fitted for a set Debye-Waller factor σ2. In the wavelet transform analysis, χ(k) exported from Athena was imported into Hama Fortran code. The parameters were an R range of 0-4 Å, a k-range of 0-11 Å−1 for Pd, and a k-weight of 3. A Morlet function with κ=10 and σ=1 was used as the mother wavelet to give the overall distribution.Electrochemical Measurements

[0075] The SNDP-Pd@HEAA film was deposited on carbon cloth and glassy carbon electrode (Φ4 mm) with a thickness of approximately 350 nm for electrochemical investigation. Electrochemical measurements were conducted in 1.0 M KOH solution at room temperature on a CHI660e electrochemical station with a three-electrode cell system. SNDP-Pd@HEAA, a Hg / HgO electrode, and a graphite rod were used as the working, reference, and counter electrodes, respectively.

[0076] To more precisely measure the intrinsic overpotential of the deposited films, linear sweep voltammetry (LSV) for the samples deposited on glassy carbon electrode was recorded at a scan rate of 5 mV s−1 to obtain the polarisation curves. Electrochemical impedance spectroscopy (EIS) was carried out from 100 kHz to 0.1 Hz. A series of cyclic voltammograms were obtained in the potential range of 0-0.1 V (vs. RHE) with scan rates ranging from 10 to 80 mV s−1 at non-faradaic overpotentials to demonstrate the current charging and discharging capacitance in estimating the double-layer capacitance (Cdl). The electrochemical surface area was obtained as Cdl / Cs, where Cdl is the measured double-layer capacitance and Cs is the specific capacitance. In the present invention, a Cs value of 0.04 mF cm−2 was assumed owing to the flat surface of SNDP-Pd@HEAA. Long-term stability tests for samples on carbon cloth were performed by continuously applying a current density of 20 and 200 mA cm−2 to the working electrode adopting a chronoamperometry method without iR loss correction. The current density was calculated from the geometric surface areas. All of the data presented were corrected for iR losses and background current, and the potentials were later converted to the reversible hydrogen electrode (RHE) scale.RHE Calibration

[0077] All of the potentials in the present invention were calibrated and converted to the RHE scale. The calibration was performed in a high-purity hydrogen-saturated electrolyte with a Pt wire and carbon rod as the working electrode and counter electrode, respectively. The Hg / HgO electrode was used as the reference electrode in 1 M KOH. The CV were measured at a scan rate of 1 mV s−1. The average of the two potentials at which the current reached zero was taken as the thermodynamic potential for the hydrogen electrode reactions. In 1 M KOH, ERHE=EHg / HgO+0.9280.DFT Calculations

[0078] Density functional theory (DFT) calculations were performed using the Cambridge Sequential Total Energy Package (CASTEP) module in Materials Studio. The generalised gradient approximation method with the Perdew-Burke-Ernzerh function (GGA-PBE) was used to describe the exchange and corrections of atomic interactions and the ultrasoft pseudo-potential method was used to describe the interactions between valence electrons and ionic cores. A plane-wave basis set with a cutoff energy of 400 eV was assigned. The Brillouin zone was sampled using a Monkhorst-Pack grid for the crystal model and a Γ point for the amorphous and crystalline / amorphous interface models. The tolerances of energy, force, and displacement for structural optimisation were 1.0×10−6 eV / atom, 0.02 eV / Å, and 0.001Å, respectively. The self-consistent field was set at 1.0×10−5 eV / atom. The H2O adsorption energies (ΔEH2O ) at the surface of catalysts were calculated according toΔ⁢EH2⁢O=Esurf+H2⁢O-Esurf-EH2⁢O(1)where Esurf and Esurf+H<sub2>2< / sub2>O are the total energies of the surface before and after H2O adsorption. EH<sub2>2< / sub2>O represents the energy of a free water molecule.The Gibbs free energies for hydrogen adsorption (ΔGH*) were calculated according to:Δ⁢GH*=Δ⁢EH*+Δ⁢Z⁢P⁢E-T⁢Δ⁢S(2)where ΔEH*, ΔZPE, T, and ΔS are the binding energy, zero point energy change, temperature, and entropy change of the H* adsorption system, respectively.The vibrational entropy of H* in the adsorbed state is generally negligible. ΔS was thus calculated as:Δ⁢S=SH*-12⁢SH2≈-12⁢SH2(3)where SH<sub2>2 < / sub2>is the entropy of the gas phase H2 under standard conditions.Moreover, ΔZPE was calculated as:Δ⁢Z⁢P⁢E=Z⁢P⁢EH*-12⁢Z⁢P⁢EH2(4)Hence, the Gibbs free energy of the adsorbed state of H* was calculated using the simplified equation:Δ⁢GH*=Δ⁢EH*+0.24 eV(5)A series of atomistic models were built to study the H2O adsorption energies and the Gibbs free energies of H* for various active sites in different regions of HEAA samples with and without elemental O. The modelling was consistent with the experimental results. Specifically, three representative models with crystal, amorphous, and crystalline / amorphous dual-phase structures (referred to as Crystal, MG and Interface, respectively) were constructed.To reveal the effect of O addition on the hydrogen evolution reaction performance, three other models with crystal, amorphous, and dual crystalline / amorphous phase structures were constructed with O addition. To obtain reliable configurations of the amorphous models, first, all atoms were randomly assigned into cubic supercells and periodic boundary conditions were applied in three directions. The amorphous models were then well relaxed and optimised to remove artificial factors. The crystalline / amorphous interface models were built by combining the crystal and amorphous models followed by further relaxation and optimisation. Using the optimised crystal, amorphous, and interface models established above, a vacuum gap approximately 15 Å wide was introduced to investigate the hydrogen evolution reaction performance of various active sites on the surfaces of these models. Hence, the H2O adsorption energies and H* Gibbs free energies of six representative models (crystal, amorphous, and interface models with and without O addition) could be investigated to unveil the atomistic mechanism that accounts for the improved hydrogen evolution reaction performance of the catalyst of the present invention.Example 2—Preparation of SNDP-Pd@HEAA CatalystsThe catalyst with novel supra-nano dual-phase structure was synthesized by introducing a large amount of oxygen innovatively. In this example, SNDP-Pd@HEAA catalysts were synthesized using double-target magnetron sputtering, a bottom-up, industrialized method that enables the large-scale production of a wide variety of nanomaterials. The fabrication method used in this work was magnetron co-sputtering (Angstrom Engineering Inc. Co., Ltd). The background vacuum was 4×10−7 Torr. HEAA and Pd targets were used for co-sputtering. The SNDP-Pd@HEAA was then deposited on different substrates (Si(001), carbon cloth, and nickel foam, Pt foil) simultaneously for different purposes.

[0086] The thickness of the films was easily controlled by the sputtering time and the composition of the films was controlled by tuning the difference in substrate-to-target distances. During co-sputtering process, the power supplied to the HEAA target with a direct-current source was set at 135 W; the power supplied to the Pd target with a radio-frequency source was set at 105 W; the flow velocity of Ar was 20 sccm and that of O2 was 1 sccm; the chamber pressure was 3 mTorr; the deposition rate was approximately 6 nm min−1; and the temperature of the substrate was below 50° C.

[0087] Additionally, a series of SNDP-M@HEAA materials (M=Ir, Pt, Ru, Au, Ag, or W) were prepared by adopting the same method.Example 3—Characterization of the SNDP-Pd@HEAA Catalysts

[0088] Referring to FIG. 1A, the X-ray diffraction patterns of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA catalysts had a broad diffraction peak without strong Bragg crystalline diffraction. This peak was much narrower than the diffraction peak of the amorphous HEAA, indicating the amorphous and ultra-small nanocrystalline nature of the catalysts. The SEM images of SNDP-Pd@HEAA deposited on carbon cloth revealed a smooth surface (FIG. 1B). Additionally, atomic force microscopy revealed the ultra-smooth surface of SNDP-Pd@HEAA, exhibiting a roughness of only approximately 1.36 nm (FIG. 1C).

[0089] The components of SNDP-Pd@HEAA were identified through EDS mapping. Referring to FIG. 1D, the SNDP-Pd@HEAA contained 25.12 at % Pd, 42.24 at % O , 2.74 at % Al, 3.35 at % Si, 2.9 at % Ti, 3.99 at % Ni, 4.62 at % Cu, 8.62 at % Zn, and 6.41 at % Zr.

[0090] The TEM image of FIG. 2A showed a homogeneous distribution of nanoparticles surrounded by a thin amorphous layer. The high-resolution STEM image in FIG. 2B further revealed an amorphous / nanocrystalline SNDP structure, such structure featured uniformly dispersed nanograins were approximately 4.5 nm in diameter with a face-centred cubic crystalline structure. Surrounding the nanocrystals was an amorphous layer approximately 1.2 nm in thickness. Referring to FIG. 2C, the above findings aligned with the selected area electron diffraction (SAED) pattern, which displayed an amorphous ring alongside several crystalline rings. These crystalline rings could be indexed to multi-crystal face-centered cubic Pd with random orientations.

[0091] The three-dimensional reconstructed TEM image showed the same SNDP structure from the horizontal region to the cross-sectional region (FIG. 3A), indicating the homogeneous SNDP structure of the SNDP-Pd@HEAA in three dimensions, which differed greatly from the granular / columnar structure of conventional sputtered films. A statistical examination of the grain-size distribution of more than 300 nanocrystals showed that the grain size had a mean value of approximately 4.76 nm, and that more than 94.47% of the nanocrystals were within the size range of 3-6 nm (FIG. 3B). A cross-sectional high-angle annular dark-field STEM (HAADF-STEM) image provided additional evidence of the nanograin nature of SNDP-Pd@HEAA (FIG. 3C). The corresponding indexed EDS line scan compositional profile (FIG. 3D) displayed sharp compositional transitions between Pd and O across the amorphous and crystalline regions. Specifically, the Pd content was higher in the nanograin regions compared to the amorphous regions, whereas the O content showed an inverse distribution relative to Pd. The other elements (e.g., Al, Zn, Ti, Zr, Si, Cu, and Ni) were homogeneously distributed in the SNDP film.

[0092] FIG. 3E showed a two-dimensional tomographic reconstruction from a typical three-dimensional atom probe tomography dataset, revealing the content variations of all the elements across a truncated plane. Specifically, the crystalline and amorphous phases were respectively enriched in Pd and O whereas Al, Zn, Ti, Zr, Si, Cu, and Ni were distributed uniformly across the two phases as regular solutes.

[0093] For comparison, the samples obtained under the same conditions except for the introduction of oxygen during the synthesis process were denoted as As-SNDP-Pd@HEAA. The pure HEAA film and pure Pd film were prepared by single-target sputtering under the same conditions. For comparison, the samples with different contents of oxygen were prepared under different flow velocities of O2. The As-SNDP-Pd@HEAA sample had a crystal-amorphous SNDP structure similar to that of SNDP-Pd@HEAA. The o-Pd and o-HEAA samples had a pure PdO crystal and purely amorphous nature, respectively. Similarly, the As-Pd and As-HEAA samples had a pure Pd crystal and purely amorphous nature, respectively.

[0094] The SNDP-Pd@HEAA samples with varying oxygen contents were produced by adjusting the oxygen gas flow rate. The elemental compositions of these samples were determined using SEM-EDS and are summarized in Table 1. The O content was positively correlated with the flow rate of the oxygen gas.TABLE 1Elemental compositions of SNDP-Pd@HEAA sampleswith different O contents obtained by SEM-EDSO2PdAlCuNiTiZnZrSiOflow rate(at %)(at %)(at %)(at %)(at %)(at %)(at %)(at %)(at %)0sccm39.003.907.406.175.6912.3911.985.757.720.15sccm36.983.727.495.875.1911.2410.865.4013.250.3sccm34.183.296.655.485.9710.1210.155.4118.750.5sccm33.883.785.884.484.078.634.825.1529.310.75sccm27.652.815.104.593.759.607.343.7435.431sccm24.522.744.623.992.908.826.413.7542.242sccm23.992.023.753.252.435.148.323.3947.713.5sccm23.511.222.382.151.011.179.732.0356.80

[0095] Referring to FIG. 4A, detailed TEM analysis showed that the SNDP structure was consistently obtained across the entire range of oxygen contents investigated. The SNDP-Pd@HEAA samples with different O contents had similar broad diffraction peaks with drift of the peak positions (FIG. 4B).

[0096] To determine the chemical states of the elements in SNDP-Pd@HEAA, XPS was conducted, as shown in FIGS. 5A-5C. The Pd 3d spectrum had two peaks located at 340.64 eV (Pd 3d3 / 2) and 335.32 eV (Pd 3d5 / 2), which were characteristic of metallic Pd (Pd0)10. Additionally, there was a slight shift towards higher energy compared to pure Pd metal, likely due to the surrounding amorphous structure. The introduction of oxygen to the SNDP caused a down-shift in the Pd 3d signals, indicating that the d-band electron structure of SNDP-Pd@HEAA could be easily regulated by oxygen atoms. Similarly, the binding energies at 951.67 and 931.85 eV revealed unitary metallic states of Cu. The Ni 2p XPS spectra showed that most of Ni were in the metallic state and only a little of the Ni were oxidated. In contrast, the Si2p XPS spectra revealed that most of the silicon was in oxidized states, with only a small amount remaining in the zero-valence state. The Al2p, Ti2p, Ti2p and Zr3d XPS spectra indicated that all these elements were in the oxidation states. The O1s spectrum could be deconvoluted into multiple peaks, indicating the complex coordination state of oxygen with other atoms in the SNDP-Pd@HEAA. These results further illustrated that the introduced oxygen preferred to react with the elements of HEAA, and that HEAA could protect the Pd from oxidation, leading to an enrichment of oxygen in the amorphous region.

[0097] Moreover, the X-ray absorption fine structure (XAFS) was measured to clarify the electronic structures and atomic structures of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA. Referring to FIG. 6A, the X-ray absorption near-edge structure spectra at the Pd K-edge indicated that elemental Pd was predominantly in the metallic state of Pd0 in both SNDP-Pd@HEAA and As-SNDP-Pd@HEAA. The significant increase in oxygen content did not affect the valence state of Pd, consistent with the previously mentioned XPS results. The corresponding Pd K-edge extended X-ray absorption fine structure (EXAFS) (FIG. 6B) and its fitting analysis (FIG. 6C and Tables 2 and 3) revealed the existence of Pd-Pd and Pd-M (M=Ni, Cu, Zn) coordination in both SNDP-Pd@HEAA and As-SNDP-Pd@HEAA.TABLE 2EXAFS fitting parameters at the Pd K-edge for SNDP-Pd@HEAA (S02 = 0.82)ShellCNR (Å)σ2ΔE0R factorPd foilPd-Pd122.74 ± 0.010.00556.5 ± 0.40.0042PdOPd-O3.8 ± 0.22.03 ± 0.010.00202.8 ± 1.10.0038Pd-Pd4.6 ± 0.33.06 ± 0.010.0033Pd-Pd14.5 ± 0.43.46 ± 0.010.0020SNDP-Pd-O0.3 ± 0.22.02 ± 0.060.00140.8 ± 1.10.0106Pd@HEAAPd-M1.0 ± 0.22.58 ± 0.010.0016Pd-Pd7.3 ± 0.52.68 ± 0.020.0100CN: coordination number; R: bond distance; σ2: Debye-Waller factor; ΔE0: inner potential correction; R factor: goodness of fit; M = Cu, Ni, Zn.TABLE 3EXAFS fitting parameters at the Pd K-edge forAs-SNDP-Pd@HEAA (S02 = 0.84)ShellCNR (Å)σ2ΔE0R factorPd foilPd-Pd122.74 ± 0.010.00564.0 ± 0.30.0021PdOPd-O3.8 ± 0.22.02 ± 0.010.00142.8 ± 1.10.0038Pd-Pd4.6 ± 0.33.06 ± 0.010.0033Pd-Pd14.5 ± 0.43.46 ± 0.010.0020As-SNDP-Pd-M6.7 ± 0.42.60 ± 0.010.0198−4.4 ± 1.3 0.0095Pd@HEAAPd-Pd4.0 ± 0.42.75 ± 0.010.0088Pd-Zr0.6 ± 0.23.00 ± 0.010.0014CN: coordination number; R: bond distance; σ2: Debye-Waller factor; ΔE0: inner potential correction; R factor: goodness of fit; M = Cu, Ni, Zn.In Table 2 and Table 3, the appearance of Pd-O coordination and the absence of Pd-Zr coordination in SNDP-Pd@HEAA, as opposed to As-SNDP-Pd@HEAA, suggested that the coordination environment was influenced by the introduction of oxygen during the preparation process. Such differences were more clearly distinguished from the wavelet transforms for k2-weighted EXAFS signals, as shown in FIG. 7.

[0099] In contrast to the significant oxidation observed in o-Pd (Table 4), the limited presence of Pd-O coordination in SNDP-Pd@HEAA, along with the simultaneous decrease in the intensities of white lines in the X-ray absorption near-edge structure spectrum compared to the PdO standard, further illustrated the minimal oxidation of Pd due to the high degree of Pd-M coordination, which reduced the likelihood of Pd oxidation.

[0100] The Pd-Pd interatomic distance of SNDP-Pd@HEAA was approximately 2.68 Å, which was slight shorter than that of As-SNDP-Pd@HEAA (approximately 2.75 Å) and Pd foil (approximately 2.74 A). Furthermore, both SNDP-Pd@HEAA and As-SNDP-Pd@HEAA exhibited lower total coordination numbers compared to Pd foil, suggesting that crystalline Pd existed in the form of small nanoparticles with a significant presence on surfaces. This observation further indicated the extensive interfaces within the distinctive SNDP structure.TABLE 4EXAFS fitting parameters at the Pd K-edge for o-Pd (S02 = 0.82)ShellCNR (Å)σ2ΔE0R factorPd foilPd-Pd122.74 ± 0.010.00557.1 ± 0.40.0041PdOPd-O3.8 ± 0.22.02 ± 0.010.00142.8 ± 1.10.0038Pd-Pd4.6 ± 0.33.06 ± 0.010.0033Pd-Pd14.5 ± 0.43.46 ± 0.010.0020o-PdPd-O2.6 ± 0.42.00 ± 0.010.00303.6 ± 1.50.0078Pd-Pd6.2 ± 0.72.77 ± 0.020.0167Pd-Pd14.9 ± 0.83.02 ± 0.010.0090Pd- Pd21.3 ± 0.23.41 ± 0.010.0011CN: coordination number; R: bond distance; σ2: Debye-Waller factor; ΔE0: inner potential correction; R factor: goodness of fit.

[0101] Additionally, all of the series of SNDP-M@HEAA materials (M=Ir, Pt, Ru, Au, Ag, or W) had similar X-ray diffraction patterns (FIG. 8A) and crystal amorphous dual-phase structures (FIG. 8B), demonstrating the universality of the method of the present invention.Example 4—Mechanisms of the HER Process

[0102] Further investigation was conducted on SNDP-Pd@HEAA as a model material to elucidate the structural advantages and mechanisms involved in the HER process.

[0103] FIGS. 9A-9B showed the electrocatalytic HER properties of the SNDP-Pd@HEAA samples. The linear sweep voltammogram curves showed that SNDP-Pd@HEAA had the highest HER performance with a low overpotential of 10.16 mV vs RHE at 10 mA cm−2, which was far superior to that of commercial 20 wt % Pt / C (34.01 mV vs RHE) and the other samples (i.e., As-SNDP-Pd@HEAA, o-Pd, As-Pd, o-HEAA, and As-HEAA).

[0104] Furthermore, the HER mechanisms for these catalysts were analysed using corresponding Tafel plots. Referring to FIGS. 10A-10B, the SNDP-Pd@HEAA catalyst exhibited the smallest Tafel slope of 30.4 mV decade−1 in the linear region, suggesting the fastest Heyrovsky-dominated Volmer-Tafel reaction mechanism during hydrogen evolution. The SNDP-Pd@HEAA samples with varying oxygen contents also displayed a similar trend.

[0105] It is well established that low charge transfer resistance indicates a superior electrocatalyst. Therefore, electrochemical impedance spectroscopy was conducted at an overpotential of 100 mV to gather data and confirm the occurrence of HER. As shown in FIG. 11, SNDP-Pd@HEAA had a much smaller diameter of the semicircular trend than the control samples, comparable to that of the carbon-containing 20 wt % Pt / C, suggesting that the unique SNDP structure in SNDP-Pd@HEAA had great potential for the optimisation of the corresponding electronic structure.

[0106] Since variations in surface area can impact HER performance, the electrochemical surface areas of the catalysts were estimated by measuring the electrochemical double-layer capacitance (Cdl) via cyclic voltammetry, representing the electrochemically active surface area (FIG. 12A). As shown in FIG. 12B, the calculated Cdl of SNDP-Pd@HEAA was 126.7 mF cm−2 and much higher than that of commercial 20 wt % Pt / C (46.0 mF cm−2), As-SNDP-Pd@HEAA (40.0 mF cm−2), and the other samples (all less than 8 mF cm−2).

[0107] As illustrated in FIG. 13A, the SNDP-Pd@HEAA electrocatalysts, both with and without the addition of O, exhibited an intrinsic dual-phase structure comprising crystalline and amorphous regions. Initially, three types of models were constructed-crystalline, amorphous, and crystalline / amorphous interface with and without the inclusion of oxygen. These models were subsequently optimized for structural integrity.

[0108] First, the adsorption energy of H2O molecules at different catalytic sites (ΔEH2O ) in the three models were calculated for the initial water adsorption step. FIGS. 13B-13C showed that the Ti, Zr, and Al sites had strong H2O adsorption in all three models, highlighting the major contribution of HEAA to ΔEH2O for the catalysts of the present invention. Notably, the increase in H2O adsorption resulting from the addition of elemental oxygen was most pronounced at the crystalline / amorphous interface.

[0109] FIG. 14 showed the atomic configurations and the corresponding electron density difference with bonding distance between the O atom in the H2O molecule and the active sites indexed after H2O adsorption at representative Pd, Ti, Zr, and Al sites in the interface models with and without elemental O. The shortening of the bonding distance between the active sites and the O atom in the H2O molecule and a left shift away from the Fermi level (EF) in the p-orbitals partial density of states (p-PDOS) of the O atom in H2O molecule (FIG. 15) revealed the physical origin of the increase in ΔEH2O due to the elemental O.

[0110] It is well known that the Gibbs free energy of H* (ΔGH*) is a key descriptor of the HER performance. A value close to zero is preferred because the HER process includes the reversible adsorption and desorption of H*, which require the interaction between catalytic sites and H* to be neither too strong nor too weak. The easier introduction of oxygen into the amorphous region resulted in less oxygen being able to coordinate directly with the active Pd centre in the crystal region.

[0111] To specify the effect of O coordination, ΔGH* values of Pd sites were compared under three conditions: 1) without O coordination, 2) with the nearest O coordination, and 3) with the next-nearest O coordination. The observation revealed that nearest O coordination negatively affected ΔGH*, whereas next-nearest O coordination proved advantageous for optimizing ΔGH*.

[0112] Calculations based on density-functional theory (DFT) were conducted to explore the atomistic physical origin of the superior HER performance of the SNDP-Pd@HEAA of the present invention. The variation in ΔGH* depicted in FIG. 16A, along with the corresponding atomic arrangements illustrated in FIGS. 16B-16C, were analyzed following the adsorption of H protons onto Pd sites situated on the catalyst surfaces of the crystal, amorphous, and crystalline / amorphous interface models. The results showed that Pd sites at the crystalline / amorphous interface had more favourable ΔGH* values than those in the crystal and amorphous models. Specifically, the Pd site with the next-nearest O coordination had a near-zero ΔGH* of 0.062 eV, indicating the positive effect of the next-nearest O coordination on the HER performance. The high content of O in the amorphous phase and the high content of Pd in the crystalline phase may lead to a high proportion of Pd sites with next-nearest O coordination.

[0113] Furthermore, the effects of the nearest and next-nearest O coordination at the Pd sites of crystalline / amorphous interface models were examined by analysing the two-dimensional electron density difference (illustrated in FIG. 17A, where Ti coordination was selected as a representative for ‘Interface’ and ‘Interface-O-NN’ models) and the d-orbital partial density of states (d-PDOS) (FIG. 17B). The observation revealed that the Pd site experienced the most significant electron loss and a leftward shift of the d-band center away from the Fermi level due to the nearest O coordination, exacerbating the HER performance. Meanwhile, the electron loss of Pd was weakened, and there was a right shift of the d-band centre toward the Fermi level when the Pd site was next-nearest neighbouring with the O atom, which effectively promoted the electron transfer and increased the strength of the interaction between H* and the Pd sites and thus optimised ΔGH*.

[0114] Apart from the Pd sites, favorable values of ΔGH* were also observed at monatomic catalytic sites, such as Pd-Al and Pd-Cu sites. This observation indicated that the synergistic effect between Pd sites and HEAA significantly contributed to the outstanding HER performance of the developed electrocatalyst (FIGS. 18A-18B), rendering the HER performance of the crystalline / amorphous dual-phase catalyst without elemental O comparable to that of commercial Pt / C.

[0115] Overall, the experiments and DFT revealed that a large number of the next-nearest O coordinated active sites at interfaces gave rise to a near-zero value of ΔGH* and strong H2O and hydrogen / proton adsorption. The promotion of H2O adsorption and hydrogen / proton adsorption contributed to the excellent HER performance of SNDP-Pd@HEAA. The next-nearest O coordination with Pd sites effectively promotes the electron transfer ability and increases the strength of interaction between H* and the Pd sites and thus optimises ΔGH* and yields excellent HER performance.Example 5—Effect of Introducing Oxygen

[0116] The introduction of oxygen may lower the overpotential and accelerated the reaction kinetics. FIGS. 19A-19C summarized the relationship between the oxygen content and the electrocatalytic performance. All SNDP-Pd@HEAA samples with varying oxygen content exhibited an electrochemically active surface area that was significantly greater than or comparable to that of 20 wt % Pt / C. This highlighted the importance of the crystal-amorphous dual-phase structure and the addition of oxygen. The results showed that the SNDP-Pd@HEAA with an O concentration of 42.24 at. % had the best electrocatalytic performance. This could be attributed to the introduction of oxygen, which weakened the adsorption energy of OH* due to a downshifted d-band center of Pd, resulting in lower impedance and a larger electrochemical surface area. However, an excessively high oxygen concentration led to severe oxidation of the metal components, as indicated by an upshifted d-band center of Pd, higher impedance, and a smaller electrochemical surface area. Therefore, the enhancement in HER performance resulting from the addition of oxygen could primarily be attributed to the optimized electronic coupling and increased surface area within the SNDP-Pd@HEAA samples.

[0117] In FIG. 20, the overpotentials at a current density of 10 mA cm−2 for previously reported HER electrocatalysts tested in alkaline media were compared. The SNDP-Pd@HEAA catalyst was shown to be competitive with the state-of-the-art HER catalysts. In particular, Table 5 listed the hydrogen evolution reaction performance of SNDP-Pd@HEAA in 1 M KOH and previously reported crystal-amorphous dual-phase catalysts.TABLE 5OverpotentialTafel slopeElectrocatalysts(at 10 mA cm−2)(mV dec−1)NoteSNDP-Pd@HEAA10.1638.9This workAs-SNDP-Pd@HEAA53.353.3This workAlMnRu23.7 / Pt-a / c-CoNiHPi1949.2Prior artCoP / MnOx13559.4

[0118] Apart from enhancing catalytic efficiency, the impact of introducing oxygen on stability was also examined. Referring to FIG. 21A, SNDP-Pd@HEAA exhibited good stability during a 100-h long-term test at a current density of 20 mA cm−2, with the overpotential of SNDP-Pd@HEAA decreasing by only approximately 17.3 mV, which was much smaller than the decrease for As-SNDP-Pd@HEAA. Following the 100-hour long-term test, the SNDP-Pd@HEAA maintained its SNDP structure and valence states, confirming the robust stability of SNDP-Pd@HEAA during HER operation. Nevertheless, at the end of the stability test, the elemental Al, Zn, Ti, Zr, and Si in As-SNDP-Pd@HEAA were noticeably oxidized (FIG. 21B), suggesting that the introduction of oxygen effectively enhanced the structural stability of SNDP-Pd@HEAA.

[0119] The concentrations of elemental Pd, Al, Zn, Ti, Zr, Si, Cu, and Ni dissolved in solution were measured at the conclusion of a 200-hour durability test under alkaline conditions, conducted at a current density of 200 mA cm−2, using inductively coupled plasma-optical emission spectrometry, as listed in Table 6.TABLE 6ICP-OES results for SNDP-Pd@HEAA after 200h at current density of 200 mA cm−2ConcentrationLimit of reporting(mmol / L)(mmol / L)Pd0.00200.00041Al0.00260.00104Zn0.00170.00009Ti0.00120.00008Zr0.00050.000078Si0.43210.0020Cu0.00230.00015Ni0.00390.00026O / / *The lowest concentration of a substance that can be reliably measured by ICP-OES.

[0120] The concentrations of all detected elements were near the detection limit of the instrumentation, consistent with the slight change observed in the XPS elemental composition analysis of SNDP-Pd@HEAA. This further highlighted the superior stability of SNDP-Pd@HEAA.

[0121] Moreover, as shown in FIGS. 22A-22F, the introduction of oxygen to the SNDP catalysts led to electrocatalytic HER and / or oxygen evolution reaction (OER) performances that surpassed those of the other samples. This further underscored the universality of oxygen addition as an effective strategy for enhancing electrocatalytic performance.Example 6—Preparation of flow-Type Membrane Exchange Assembly Alkaline Water Electrocatalysis Cell

[0122] The SNDP-Pd@HEAA deposited on carbon felt and SNDP-Ir@HEAA deposited on a porous titanium sheet were respectively used as the cathode and anode.

[0123] Referring to FIG. 23, it was observed that the SNDP-Pd@HEAAISNDP-Ir@HEAA electrolyser operated steadily for 1000 hours at 500 mA cm−2, with no significant reduction in voltage relative to the initial state.

[0124] The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

[0125] The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated.DEFINITIONS

[0126] Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and / or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the present invention.

[0127] Furthermore, throughout the specification and claims, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0128] As used herein and not otherwise defined, the terms “substantially,”“substantial,”“approximately” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can encompass instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0129] References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0130] In the methods of preparation described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E, and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps can also be repeated. Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately.

[0131] The term “double layer capacitance” refers to the capacitance effect formed between the electrode surface and the electrolyte solution, where the separation of charges between the adsorbed charges on the electrode surface and the corresponding ions in the electrolyte creates a charge barrier. This charge barrier can store charge and produce a capacitance effect under the influence of an electric field.

[0132] The term “at. %” stands for atomic percent. It is a unit of concentration used in chemistry and materials science to express the proportion of one type of atom relative to the total number of atoms in a mixture, compound, or alloy. For example, in a sample with 10 at. % of element A and 90 at. % of element B, it means that out of every 100 atoms in the sample, 10 are atoms of element A and 90 are atoms of element B.

[0133] Other definitions for selected terms used herein may be found within the detailed description of the present invention and apply throughout. Unless otherwise defined, all other technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the present invention belongs.

Examples

example

Example 1—Materials and Methods

Materials

[0073]Raw element granules of aluminium (Al), zinc (Zn), titanium (Ti), zirconium (Zr), silicon (Si), copper (Cu), and nickel (Ni) with a purity higher than 99.95% were mixed by China Material Technology Co., Ltd to achieve the high-entropy amorphous alloy (HEAA) sputtering target with a theoretical atomic composition (at %) of Al0.5ZnTiZrSiCuNi. The pure palladium (Pd) target with a purity higher than 99.99% was purchased from Angstrom Engineering Inc. Co., Ltd. Analytical grade potassium hydroxide (KOH), and absolute ethanol were supplied by Sigma Aldrich. All of the solutions were prepared with Milli-Q water (18.2 MΩcm).

Material Characterization

[0074]The samples were characterised through scanning electron microscopy (SEM, Philips XL-30 FESEM), atomic force microscopy (AFM, Bruker Icon), and high-resolution transmission electron microscopy (TEM, JEOL TEM 2100F FEG operated with an accelerating voltage of 200 kV). Atomic-resolution scanning ...

example 2

Preparation of SNDP-Pd@HEAA Catalysts

The catalyst with novel supra-nano dual-phase structure was synthesized by introducing a large amount of oxygen innovatively. In this example, SNDP-Pd@HEAA catalysts were synthesized using double-target magnetron sputtering, a bottom-up, industrialized method that enables the large-scale production of a wide variety of nanomaterials. The fabrication method used in this work was magnetron co-sputtering (Angstrom Engineering Inc. Co., Ltd). The background vacuum was 4×10−7 Torr. HEAA and Pd targets were used for co-sputtering. The SNDP-Pd@HEAA was then deposited on different substrates (Si(001), carbon cloth, and nickel foam, Pt foil) simultaneously for different purposes.

[0086]The thickness of the films was easily controlled by the sputtering time and the composition of the films was controlled by tuning the difference in substrate-to-target distances. During co-sputtering process, the power supplied to the HEAA target with a direct-current source...

example 3

Characterization of the SNDP-Pd@HEAA Catalysts

[0088]Referring to FIG. 1A, the X-ray diffraction patterns of SNDP-Pd@HEAA and As-SNDP-Pd@HEAA catalysts had a broad diffraction peak without strong Bragg crystalline diffraction. This peak was much narrower than the diffraction peak of the amorphous HEAA, indicating the amorphous and ultra-small nanocrystalline nature of the catalysts. The SEM images of SNDP-Pd@HEAA deposited on carbon cloth revealed a smooth surface (FIG. 1B). Additionally, atomic force microscopy revealed the ultra-smooth surface of SNDP-Pd@HEAA, exhibiting a roughness of only approximately 1.36 nm (FIG. 1C).

[0089]The components of SNDP-Pd@HEAA were identified through EDS mapping. Referring to FIG. 1D, the SNDP-Pd@HEAA contained 25.12 at % Pd, 42.24 at % O , 2.74 at % Al, 3.35 at % Si, 2.9 at % Ti, 3.99 at % Ni, 4.62 at % Cu, 8.62 at % Zn, and 6.41 at % Zr.

[0090]The TEM image of FIG. 2A showed a homogeneous distribution of nanoparticles surrounded by a thin amorphous ...

Claims

1. An oxygen-dominated supra-nano dual-phase catalytic reaction material on a substrate, comprising a uniform oxygen-enriched amorphous shell and a core encapsulated within the uniform oxygen-enriched amorphous shell, wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material has an intrinsic crystal-amorphous dual-phased structure, and wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material exhibits an overpotential of 10 to 25 mV vs RHE at 10 mA cm−2.

2. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the uniform oxygen-enriched amorphous shell is made from a high-entropy amorphous alloy comprising AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy.

3. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the core is made from at least one transition metal comprising palladium, platinum, iridium, ruthenium, rhodium, gold, silver, or non-noble metal of vanadium, molybdenum, tungsten, and even NiMo, NiW binary alloy.

4. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the core is 1-10 nm in diameter and the uniform oxygen-enriched amorphous shell has a thickness of approximately 1-5 nm.

5. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 20-30 at % of Pd, 10-50 at % of O, 1-5 at % of Al, 5-20 at % of Si, 5-20 at % of Ti, 5-20 at % of Ni, 5-20 at % of Cu, 1-15 at % of Zn, and 5-20 at % of Zr.

6. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 10-30 at % of Pt, 10-40 at % of O, 5-20 at % of Fe, 5-20 at % of Co, 5-20 at % of Ni, 1-15 at % of Mo, 1-10 at % of P, and 1-10 at % of B.

7. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the substrate comprises nickel foam, carbon cloth, carbon paper, silicon wafer, titanium sheet, or platinum foil.

8. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the crystal phase has a face-centred cubic structure and the amorphous phase has a typical diffused-ring structure.

9. The oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1, wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material demonstrates a stability in a 100-hour long-term test at a current density of 20 mA cm−2 in a three-electrode system and can operate steadily for 1000 h at a current density of 500 mA cm−2 in a flow-type membrane exchange assembly alkaline water electrocatalysis cell.

10. A water splitting electrode made from the oxygen-dominated supra-nano dual-phase catalytic reaction material of claim 1.

11. A method for fabricating an oxygen-dominated supra-nano dual-phase catalytic reaction material, comprising co-sputtering a crystal metal target and a high-entropy amorphous alloy target on a substrate by industrial magnetron sputtering, and wherein oxygen gas is introduced during the magnetron sputtering process.

12. The method of claim 11, wherein crystal metal target is selected from one or more noble metal of palladium, platinum, iridium, ruthenium, rhodium, gold, silver, or non-noble metal of vanadium, molybdenum, tungsten, and even NiMo, NiW binary alloy.

13. The method of claim 11, wherein the oxygen gas has a flow velocity ranging from approximately 0.01 sccm to 50 sccm.

14. The method of claim 11, wherein the high-entropy amorphous alloy target is a multi-component alloy comprising AlZnTiZrSiCuNi-containing alloy, FeCoNiMoPB-containing alloy.

15. The method of claim 14, wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 20-30 at % of Pd, 10-50 at % of O, 1-5 at % of Al, 5-20 at % of Si, 5-20 at % of Ti, 5-20 at % of Ni, 5-20 at % of Cu, 1-15 at % of Zn, and 5-20 at % of Zr.

16. The method of claim 14, wherein the oxygen-dominated supra-nano dual-phase catalytic reaction material contains 10-30 at % of Pt, 10-40 at % of O, 5-20 at % of Fe, 5-20 at % of Co, 5-20 at % of Ni, 1-15 at % of Mo, 1-10 at % of P, and 1-10 at % of B.

17. The method of claim 11, wherein the industrial magnetron sputtering adopts a sputtering temperature at approximately 0.1 to 200° C.

18. The method of claim 11, further comprising applying different power to the crystal metal target and the high-entropy amorphous alloy target.

19. The method of claim 12, wherein the substrate has a rotation speed in the range from 0.1 rpm to 20 rpm during sputtering.

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