Hydrothermally synthesized Fe-NiO catalyst and application thereof in methanol electrooxidation
By preparing an iron-doped nickel oxide catalyst, the problem of high energy consumption in the anodic oxygen evolution reaction during water electrolysis for hydrogen production was solved, achieving efficient and selective methanol oxidation to formic acid with good stability and low cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-17
- Publication Date
- 2026-04-14
AI Technical Summary
The existing process for producing hydrogen by water electrolysis has high energy consumption and low product value due to the oxygen evolution reaction at the anode. Furthermore, it is difficult to balance the activity, selectivity, and stability of existing methanol oxidation catalysts.
Iron-doped nickel oxide (Fe-NiO) catalysts were prepared by synthesizing and doping with iron via a hydrothermal method, thereby controlling the electronic structure of nickel and optimizing the chemical properties of the active sites.
It significantly improves the catalytic activity and selectivity of methanol oxidation reaction, reduces energy consumption, achieves efficient production of formic acid, and also has good long-term stability and low cost characteristics.
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Figure CN121853009A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochemical catalysis technology, specifically relating to the synthesis of an iron-doped nickel oxide catalyst and its application in the selective oxidation of methanol to formic acid. Background Technology
[0002] With the global energy crisis and environmental pollution becoming increasingly severe, the development of clean and renewable energy has become a major focus of scientific research. Hydrogen energy, due to its high gravimetric energy density and environmentally friendly combustion products, possesses the dual attributes of being both an important industrial raw material and an increasingly crucial clean energy carrier. Among various hydrogen production technologies, water electrolysis is one of the most mature and scalable technologies (Small 2022, 18, 2202336). Its core principle involves a hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode. Despite the promising prospects of water electrolysis, the kinetics of the anodic oxygen evolution reaction are very slow, requiring a large overpotential to achieve the current density needed for industrial applications. This fundamentally limits the overall efficiency of water electrolysis (Joule 2021, 5, 1704–1731). This high-energy-consuming step significantly increases operating costs, becoming a major bottleneck restricting large-scale green hydrogen production.
[0003] Replacing the oxygen evolution reaction (OER) with the electro-oxidation of small-molecule organic compounds is an effective strategy for reducing anodic overpotential and simultaneously producing high-value-added chemicals (Acc. Chem. Res. 2018, 51, 1571–1580). Among numerous candidate molecules, methanol has attracted much attention due to its low price, wide availability, convenient storage and transportation, and excellent intrinsic electro-oxidation kinetics. Anodic methanol oxidation reaction (MOR) can not only reduce hydrogen production energy consumption but also generate formate with high selectivity (ACS Energy Lett., 2024, 9, 853–879). Formic acid is an important chemical intermediate widely used in pharmaceuticals, leather processing, and carbon capture. However, to achieve this dual-function objective, it is urgent to design electrocatalysts that combine high methanol oxidation activity, excellent formate selectivity, long-term stability, and low cost.
[0004] While platinum-based catalysts have demonstrated excellent methanol oxidation performance and have been extensively studied in fuel cell systems, their scarcity and high cost hinder large-scale application (Chem. Rev. 2014, 114, 12397–12429). In contrast, nickel-based compounds have attracted widespread attention in recent years as highly promising alternative materials, especially under alkaline conditions, where they can rapidly form the highly oxidizing active species nickel hydroxyl oxide (NiOOH).
[0005] To further improve methanol oxidation efficiency, researchers have developed various strategies to optimize the electronic structure of nickel-based catalysts through doping or component modulation. The introduction of heteroatoms can promote the adsorption and activation of reaction intermediates, alter the redox properties of nickel active sites, and regulate the reaction pathway. For example, previous studies have shown that doping nickel-based chalcogenides with iron can significantly improve methanol oxidation activity and formate selectivity (J. Energy Chem. 2026, 112, 720–729); while introducing manganese into nickel hydroxide can simultaneously improve the catalytic performance and structural stability of the catalyst (J. Colloid Interface Sci. 2024, 663, 971–980).
[0006] Therefore, this study prepared an iron-doped nickel oxide (Fe–NiO) electrocatalyst, which exhibited significantly enhanced catalytic activity and selectivity for the electrooxidation of methanol to formate. Iron-doped nickel oxide is an effective catalyst modification strategy that allows for precise control of the chemical properties of active sites, achieving efficient, highly selective, and low-energy-consumption methanol oxidation, thus providing technical support for coupled hydrogen production processes. Summary of the Invention
[0007] The purpose of this invention is to provide an iron-doped nickel oxide catalyst and its application in the selective oxidation of methanol to formic acid, in order to solve the problems of high energy consumption and low product value in the oxygen evolution reaction during the existing water electrolysis hydrogen production process, as well as the difficulty in balancing the activity, selectivity and stability of existing methanol oxidation catalysts.
[0008] Technical solution
[0009] To achieve the above objectives, the chemical reagents used in this invention are: nickel chloride (NiCl2·6H2O, 99%, Sigma-Aldrich, Shanghai, China), ferric chloride (FeCl3, 98%, Miura, Shanghai, China), urea (CH4N2O, 99%, Titan, Shanghai, China), anhydrous methanol (MeOH, 99.8%, Sigma-Aldrich, Shanghai, China), potassium hydroxide (KOH, 90%, Tansole, Shanghai, China), Nafion solution (10 wt.% perfluorinated ion exchange resin aqueous solution, Shanghai, China), and carbon black (CB, Vulcan XC72, Shanghai, China). The experimental water is self-prepared high-purity water (resistivity 18.2 MΩ·cm).
[0010] A method for preparing an iron-doped nickel catalyst mainly includes the following steps:
[0011] 1. Weigh out nickel chloride (NiCl2·6H2O), ferric chloride (FeCl3), and 0.3g of urea according to a nickel / iron molar ratio of 3 / 1, dissolve them in 30mL of pure water, and sonicate the solution for 3min;
[0012] 2. Transfer the solution to a polytetrafluoroethylene-lined autoclave and react at 130°C for 3 hours. After naturally cooling to room temperature, collect the precipitate and wash it three times each with deionized water and ethanol.
[0013] 3. The vacuum-dried powder was annealed in air at 350°C for 3 hours to obtain an iron-doped nickel oxide (Fe-NiO) catalyst, which was then sealed and stored for later use.
[0014] To facilitate comparison of electrocatalytic properties, pure nickel oxide (NiO) and iron oxide (Fe2O3) nanomaterials were used as control samples and synthesized under the same conditions in solutions without the addition of iron- or nickel-containing precursors. Detailed Implementation
[0015] like Figure 1 As shown, the application of Fe-NiO, NiO, and Fe2O3 catalytic materials obtained by the above preparation method in the selective oxidation of methanol to formic acid mainly includes the following steps:
[0016] Characterization of catalysts
[0017] First, XRD analysis was performed on Fe-NiO, NiO, and Fe2O3 using an X-ray diffractometer. The results are as follows: Figure 1As shown in the XRD patterns, the crystal structures of Fe-NiO, NiO, and the standard NiO card (PDF#89-5881) are highly consistent. Compared to NiO, the characteristic peaks of Fe-NiO shift to a lower angle, confirming that Fe has been successfully doped into the NiO lattice. Furthermore, the synthesized Fe2O3 (standard card PDF#72-0469) is a pure phase.
[0018] Secondly, such as Figure 2 As shown, pure NiO exhibits a relatively uniform nanoparticle (NP) morphology with an average size of approximately 15 nm. Figure 3 As shown, Fe2O3 was identified as nanorods (NRs) with a length of approximately 65 nm and a width of approximately 9 nm.
[0019] like Figure 4 As shown, the morphology of Fe-NiO is basically similar to that of Fe2O3, exhibiting a nanorod shape with an average length of approximately 50 nm and a width of approximately 8 nm. Figure 4 SEM-EDS analysis confirmed the presence of Fe, Ni, and O elements in Fe-NiO, with atomic percentages of 11.62%, 22.60%, and 65.78%, respectively.
[0020] The Fe-NiO catalyst was analyzed by HRTEM using a JEM-F200 transmission electron microscope, such as... Figure 5 As shown in figure a, the clear lattice fringes further confirm the crystal structure of the catalyst; as Figure 5 As shown in b, nickel, iron, and oxygen elements are uniformly distributed in the nanoparticles.
[0021] Preparation of working electrode
[0022] 1. Preparation of catalyst slurry: Weigh 20 mg of nanomaterials and 10 mg of carbon black (CB), add them to 6 mL of a mixed solution of Milli-Q water and ethanol (volume ratio 1:1), then add 200 μL of Nafion solution, and place the mixture in an ultrasonic instrument for vigorous sonication for 1 hour to obtain a uniformly dispersed catalyst slurry.
[0023] 2. Preparation of the working electrode: A 5 mm diameter glassy carbon (GC) electrode was polished to a mirror finish on a polishing cloth using a 0.05 μm alumina slurry. It was then rinsed thoroughly with Milli-Q water and ethanol, respectively, and air-dried at room temperature. 10 μL of the catalyst slurry was drop-coated onto the GC electrode surface using a pipette and allowed to air-dry naturally at room temperature to obtain the working electrode.
[0024] Electrochemical performance testing
[0025] Electrocatalytic properties were tested using a three-electrode system on a CorrTest (CS2350H) electrochemical workstation. The working electrode was a catalyst-covered GC electrode, the counter electrode was a platinum wire, and the reference electrode was a Hg / HgO electrode.
[0026] The electrolyte solution was a 1M KOH solution. Solutions with and without 1M methanol were tested. First, as... Figure 6 The results show that the NiO-based electrode exhibits clear redox peaks, corresponding to the reversible Ni(OH)₂ / NiOOH conversion, with peak current densities of 6.5 mA and -5.3 mA cm⁻¹ at 1.33 V and 1.24 V, respectively. -2 When Fe is present in the NiO-based electrode, the peak current densities at 1.37V and 1.22V are 13.7 and -12.3 mA cm⁻¹, respectively. -2 Furthermore, no significant redox properties were observed in the Fe2O3-based electrode. The lack of observable redox features in Fe2O3 indicates that Fe lacks OER activity under alkaline conditions, suggesting that Ni is the dominant active site, while Fe acts as an electron promoter to modulate the oxidation state of Ni and improve catalytic kinetics.
[0027] like Figure 6 As shown in b, the addition of 1M methanol to the electrolyte significantly increased the anodic current density of all electrodes, confirming the activity of the metal's MOR. At an applied voltage of 1.6V, the Fe-NiO-based electrode provided the highest current density (146.9 mA cm⁻¹). -2 ), far exceeding nickel oxide (40.1 mA cm). -2 ) and iron dioxide (2.5 mA cm -2 In contrast, the increase in MOR current density obtained by adding 1M methanol to 1M KOH solution indicates that the OER reaction was successfully substituted.
[0028] To verify the long-term stability of the electrode material and the Faraday efficiency of methanol oxidation, a chronoamperometry (CA) test was conducted for 24 hours at 1.6V in 1M KOH and 1M methanol solutions. Figure 7 As shown in figure a, the current density of the Fe-NiO electrode material ranges from 152.8 mA / cm². -2 Gradually decreased to 83.4 mA cm -2 However, the observed current density of the NiO electrode is relatively stable, at approximately 45 mA cm⁻¹. -2 ( Figure 7 b), which is much higher than the current density obtained by the Fe2O3 electrode. Figure 7 c).
[0029] To assess the amount of formic acid produced, the electrolyte after a 24-hour CA test was analyzed by ion chromatography (IC) using an ALXILAB IC2100 instrument. The IC spectra of the three electrodes (Fe-NiO) were used for analysis. Figure 7 The illustration in a, NiO is Figure 7 The illustration in b and Fe2O3 are... Figure 7 (Illustration in c) Using a formate solution of known concentration as an internal standard, the formate concentrations of the Fe-NiO, NiO, and Fe2O3 electrodes were determined to be 10.41, 2.91, and 0.072 mmol / L, respectively. -1 The corresponding formic acid production amounts were 324.90, 90.79, and 2.23 μmol, respectively.
[0030] The Faradaic efficiency (FE) for the conversion of methanol to formate is calculated using the following formula:
[0031] FE (%) = (Amount of formate × n × F) / (Q) × 100%
[0032] The amount of formate was determined by ion chromatography (IC), where n is the number of electrons transferred from methanol to formic acid, and F is the Faraday constant (96485 C mol⁻¹). 1 Q is the total charge passing through during the CA process.
[0033] like Figure 7 As shown in Figure d, Fe-Ni achieved the highest Faradaic efficiency of 99.9%, followed by NiO (93.2%) and Fe2O3 (39.9%). Therefore, the higher current density in Fe-NiO and the Faradaic efficiency of formate indicate that iron doping not only improves the electro-oxidation activity of methanol but also suppresses other possible side reactions, thereby achieving highly selective formic acid formation.
[0034] Beneficial effects
[0035] Compared with the prior art, the present invention has the following beneficial effects:
[0036] 1. The iron-doped nickel oxide (Fe-NiO) catalyst prepared in this invention effectively lowers the energy barrier for the conversion of methanol to formate by modulating the electronic structure of nickel oxide through iron doping, thus significantly improving catalytic activity. In a 1M KOH solution containing 1M methanol, the methanol oxidation reaction (MOR) current density reaches 146.9 mA cm⁻¹ at 1.6 V (relative to the reversible hydrogen electrode). -2 The performance is significantly better than that of undoped NiO and Fe2O3 materials.
[0037] 2. After long-term stability testing, operating at 1.6V (relative to the reversible hydrogen electrode) for 24 hours, the initial current density was 152.8 mA cm⁻¹. -2 Ultimately, it remained stable at 83.4 mA cm⁻¹ -2 It exhibits good stability. Ion chromatography analysis shows that the Faraday efficiency of formate formation remains as high as 99.9%.
[0038] 3. The raw materials used in this invention are low-cost, the preparation process is relatively simple, and it is easy to scale up production. When applied to the selective oxidation of methanol to synthesize formic acid, hydrogen can be generated at the cathode, which improves the energy efficiency and economic benefits of the entire electrolysis process and has broad application prospects. Attached Figure Description
[0039] Figure 1 Schematic diagram and XRD pattern of hydrothermal synthesis of iron-doped nickel oxide (Fe-NiO) nanorods;
[0040] Figure 2 TEM image of NiO;
[0041] Figure 3 TEM image of Fe2O3;
[0042] Figure 4 SEM images and EDS results of Fe-NiO;
[0043] Figure 5 (a) HRTEM image and lattice analysis within the red box area; (b) EELS elemental distribution maps of Ni, Fe, and O;
[0044] Figure 6 CV curves of Fe-NiO, NiO and Fe2O3 electrode materials in 1M KOH (a) without and (b) with 1M methanol;
[0045] Figure 7 (a) CA curves of methanol oxidation at 1.6V for 24 hours for Fe-NiO, (b) NiO and (c) Fe2O3 electrode materials, with the inset showing the ion chromatograms after the stability test; (d) Formate concentration and FE value of Fe-NiO, NiO and Fe2O3 electrode materials.
Claims
1. An iron-doped nickel oxide (Fe-NiO) nanorod catalyst, characterized in that, The catalyst is prepared from nickel chloride (NiCl2·6H2O) and ferric chloride (FeCl3) as raw materials. The atomic percentages of Fe, Ni and O elements in the catalyst are 11.62%, 22.60% and 65.78%, respectively. The crystal structure matches the NiO standard card (PDF#89-5881), and the characteristic peaks are shifted to a lower angle relative to NiO.
2. A method for preparing the iron-doped nickel oxide catalyst as described in claim 1, characterized in that, Includes the following steps: (1) Weigh nickel chloride (NiCl2·6H2O) and ferric chloride (FeCl3) and 0.3g urea according to the nickel:iron molar ratio of 3:1, dissolve them in 30mL of distilled water, and sonicate for 3min to obtain a homogeneous solution; (2) Transfer the solution obtained in step 1 to a high-pressure reactor lined with polytetrafluoroethylene, react at 130°C for 3 hours, collect the precipitate after naturally cooling to room temperature, and wash it three times with deionized water and ethanol alternately. (3) The precipitate after washing in step 2 is dried, then annealed in air at 350°C for 3 hours, cooled and sealed for storage to obtain Fe-NiO nanomaterials.
3. The preparation method according to claim 2, characterized in that, The distilled water mentioned in step 1 is high-purity water with a resistivity of 18.2 MΩ·cm, and the drying process in step 3 is vacuum drying.
4. An application of the Fe-NiO nanorods as described in claim 1, characterized in that, The catalyst is used for the selective oxidation of methanol to formic acid via electrocatalysis, and its application scenario is an alkaline electrolyte system.
5. The application as described in claim 4, characterized in that, The alkaline electrolyte system is a mixed solution containing 1M KOH and 1M methanol. The electrocatalytic reaction conditions are as follows: a glassy carbon electrode loaded with the catalyst is used as the working electrode, a platinum wire is used as the counter electrode, Hg / HgO is used as the reference electrode, and the reaction voltage is 1.6V (relative to the reversible hydrogen electrode).
6. The application as described in claim 4, characterized in that, In the methanol oxidation reaction, the catalyst exhibits a methanol oxidation current density of 152.8 mA cm⁻¹ at a voltage of 1.6 V. -2 After 24 hours of continuous reaction, the current density remained at 83 mA cm⁻¹. -2 The Faraday efficiency of formate formation is approximately 99.9%.