Corrosion-resistant metal electrode and device

Abstract

The present invention provides: a corrosion-resistant metal electrode in which a corrosion phenomenon is suppressed; and a device. A corrosion-resistant metal electrode (1) according to the present invention is used in a device (10) for detecting and / or measuring a substance, is in contact with a solution containing cations in a state of being negatively polarized with respect to a standard hydrogen electrode, and comprises an alloy of which the main component is platinum and an accessory component is a first transition metal. The atomic ratio of platinum contained in the outermost surface single atomic layer (1a) of the alloy is preferably larger than the atomic ratio of platinum contained in the entirety of corrosion-resistant metal electrode (1). The atomic ratio of platinum in the outermost surface single atomic layer (1a) of a bimetal surface (1b) comprising the platinum and the first transition metal is preferably larger than the atomic ratio of platinum contained in the entirety of the bimetal surface (1b). A device (10) according to the present invention is provided with the corrosion-resistant metal electrode (1).

Description

Corrosion-resistant metal electrodes and devices

[0001] The present invention relates to corrosion-resistant metal electrodes and devices.

[0002] In recent years, cathodic corrosion, the corrosion of metals such as platinum (Pt) in the presence of cations under reducing conditions (negative potential application), has attracted increasing attention and has been the subject of intensive research. Non-Patent Document 1 provides a comprehensive explanation of cathodic corrosion of metal electrodes and explains methods for preventing it, based on numerous published literature at the time of publication. For example, Non-Patent Document 1 describes two general strategies for reducing or suppressing cathodic corrosion of electrodes in reductive organic electrochemical reactions: cation additives and alloying. Generally, reductive electrosynthesis proceeds with greater activity and selectivity when an electrosynthesized active base material is used as an electrode. It is explained that alloying the electrosynthesized active base material with different components or introducing a small amount of active metal into the base material is an effective approach to combat cathodic corrosion. Regarding alloying, Non-Patent Document 1 cites leaded bronze (CuSnPb) as an example. However, there is no data or clear description of the mechanism regarding lead bronze, and only a brief mention and examples of some chemical formulas are given.

[0003] Tom Wirtanen, Tobias Prenzel, Jean-Philippe Tessonnier, and Siegfried R. Waldvogel, “Cathodic Corrosion of Metal Electrodes How to Prevent It in Electroorganic Synthesis,” Chem. Rev. 2021, 121, 10241-10270

[0004] Due to cathodic corrosion, Pt electrodes constituting sensors that electrochemically detect substances in solution can corrode due to negative potential in cation-containing solutions during measurement and treatment before and after measurement, resulting in platinum elution and roughening of the electrode surface. Figure 20 shows SEM images of platinum electrodes treated at negative potential in 5M LiOH, 5M NaOH, and 5M KOH aqueous solutions. In the figure, the scale bar in the upper SEM image for 5M LiOH is 250 nm, and the scale bar in the lower SEM image is 100 nm. The scale bar in the upper SEM image for 5M NaOH is 500 nm, and the scale bar in the lower SEM image is 250 nm. The scale bar in the upper SEM image for 5M KOH is 500 nm, and the scale bar in the lower SEM image is 250 nm. As is clear from Figure 20, the electrode surface becomes roughened due to negative potential in cation-containing solutions. Furthermore, as shown in the above SEM images in 5M NaOH and 5M KOH, when grain boundaries are present, cathodic corrosion also progresses at the grain boundaries.

[0005] Although promising insights have been gained in understanding the intermediates involved in cathodic corrosion of Pt electrodes, as described in Non-Patent Document 1, there has been little further exploration into methods for slowing or preventing cathodic corrosion of Pt electrodes. Furthermore, as discussed in the Examples section below, Non-Patent Document 1 notes that in a recent review of cathodic corrosion and "how to prevent it," alloying has often proven to be a successful strategy for mitigating cathodic corrosion of various metals. However, this approach has primarily been applied to post-transition metals such as lead, a commonly used electrode material in reductive organic electrosynthesis, with clear counterexamples of platinum-based alloys that appear not to be protected from cathodic corrosion. A17, A18, A19. Elucidating the mechanisms by which (platinum) alloys may be protected from cathodic corrosion phenomena is clearly of great interest for their use as stable cathodes in organic electrosynthesis and electrolysis devices, as well as other electrochemical devices where the cathode may be exposed to very negative potentials.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a corrosion-resistant metal electrode and a device in which corrosion phenomena are suppressed.

[0007] The corrosion-resistant metal electrode according to the present invention, which solves the above-mentioned problems, is used in a device for detecting and / or measuring a substance, and is a corrosion-resistant metal electrode that comes into contact with a solution containing a cation while being negatively polarized with respect to a standard hydrogen electrode, and is made of an alloy whose main component is platinum and whose secondary component is a first transition metal.

[0008] The present invention can provide a corrosion-resistant metal electrode and device in which corrosion phenomena are suppressed.

[0009] Schematic diagram for explaining an example of the configuration of a corrosion-resistant metal electrode 1. An explanatory diagram for explaining the cathodic corrosion mechanism and cathodic corrosion inhibition mechanism using platinum as an example. Schematic diagram for explaining an example of the configuration of the surface of the corrosion-resistant metal electrode 1. An explanatory diagram for explaining the form that can be taken as a bimetal surface 1b. A graph showing the amount of Pt eluted from the surface of the corrosion-resistant metal electrode 1 in a state polarized to -1.0 V relative to a standard hydrogen electrode. Cathodic corrosion is observed when Pt single crystals and Pt ３ An explanatory diagram showing the effect on Ni single crystals. ３ A graph comparing the amounts of Pt and Ni dissolved when a corrosion reaction is performed on a Ni single crystal. A schematic diagram showing the configuration of the device 10. (Figure M1): (A) -3.0 V ＲＨＥ for 30 min, 0.1 M H in ∼7.5 M (30 wt %) NaOH ２ SO ４ The Pt before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion ３ Cyclic voltammetry of Ni bead electrodes. Pt before (B) and after (C) cathodic corrosion. ３ Corresponding SEM image of the Ni bead electrode (Fig. M1): (D) -3.0 V ＲＨＥ for 30 min, 0.1 M H in ∼7.5 M (30 wt %) NaOH ２ SO ４(G) Cyclic voltammetry of a Pt bead electrode before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion. Corresponding SEM images of a Pt bead electrode before (E) and after (F) cathodic corrosion. (Fig. M1): (G) Pt bead electrode and Pt ３ Ni bead electrode -3.0 V ＲＨＥ ICP-MS measurements of Pt and Ni dissolved in electrolyte solutions after cathodic corrosion in ∼7.5 M (30 wt %) NaOH for 30 min at 3.0 V (Figure M2): (A) in ∼7.5 M (30 wt %) NaOH at 3.0 V, ＲＨＥ Before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion at 0.1 MH for 1 minute. ２ SO ４ Cyclic voltammetry of a Pt(111) single crystal electrode in 7.5 M NaOH at -3.0 V (Fig. M2). ＲＨＥ (B) AFM height images of a Pt(111) single crystal electrode before (B) and after (C) cathodic corrosion for 1 min at 0.1 M H. (D) A 1 × 1 μm area image shows a well-defined triangular etch pit in the marked dashed square in (C). (E) 0.1 M H (Fig. M2), respectively. ２ SO ４ Before cathodic corrosion in 7.5 M (30 wt %) NaOH (dark red curve (dark gray curve in the figure)) and after cathodic corrosion in 7.5 M (30 wt %) NaOH (-3.0 V) ＲＨＥ Pt after cathodic corrosion for 15 minutes (red curve (medium gray curve in the figure)) and 30 minutes (light red curve (light gray curve in the figure)) ３ Cyclic voltammetry of a Ni(111)-Pt skin single crystal electrode. For comparison, a blank voltammogram (black curve) of a Pt(111) single crystal electrode recorded under the same conditions is shown. (Fig. M2): (F) Pt before cathodic corrosion and (G) after 15 and (H) 30 minutes of cathodic corrosion, respectively. ３AFM height image of a Ni(111)-Pt skin single crystal electrode. (Fig. S1): SEM image of the Pt bead surface after cathodic corrosion treatment under the same conditions as in Fig. M1 in the main text. (Fig. S2): (A) Pt immersed in 7.5 M NaOH electrolyte solution as in Fig. M1 in the main text. ３ Current-time (chronoamperometry) plots of cathodic polarization at −3.0 V for (A) Ni and (B) Pt bead electrodes. (Fig. S4): (A) 0.1 M H O before (black curve) and after (red curve (gray curve in the same figure)) cathodic corrosion in 7.5 M NaOH at −3.0 V for 30 min. ２ SO ４ Pt in ３ Cyclic voltammetry of Fe bead electrodes. Pt before (B) and after (C) cathodic corrosion. ３ Corresponding SEM images of the Fe bead electrode. (Fig. S5): Pt bead electrode and Pt ３ ICP-MS measurement results of the amount of Pt contained in the electrolyte solution collected after cathodic corrosion of Me (Me = Fe, Co, Ni, Pd) bead electrodes in 7.5 M NaOH at -3.0 V for 30 minutes. (Figure S6): (A) 0.1 M H 2 O before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion in 7.5 M (30 wt%) NaOH at -3.0 V for 30 minutes. ２ SO ４ Pt in ３ Cyclic voltammetry of a Pd bead electrode. Pt before (B) and after (C) and (D) cathodic corrosion. ３ Corresponding SEM images of Pd bead electrodes. (Fig. S7): Pt(111) and Pt ３ Cyclic voltammograms of the Me(111)-Pt skin single crystal electrode (Fig. S8): before (dark red curve) and after cathodic polarization at −3.0 V for 15 min (red curve) and 30 min (light red curve) in 7.5 M NaOH with 0.1 M H ２ SO ４ Pt recorded in ３Cyclic voltammograms of Ni(111)-Pt skin single crystal electrodes (Figure S9): (A) in 7.5 M NaOH, -3.0 V ＲＨＥ 0.1 MH before (dark green curve) and after cathodic polarization for 15 minutes (green curve) and 30 minutes (light green curve) ２ SO ４ Pt recorded in ３ Cyclic voltammograms of Co(111)-Pt skin single crystal electrodes (Fig. S9): Pt ３ Corresponding AFM height images of the Co(111)-Pt skin single crystal electrode surface before (B), (D), and after (C) 15 and (E) 30 min of cathodic polarization (Fig. S10): (A) Before (brown curve (gray curve)) and after (yellow curve (light gray curve)) 15 min of cathodic polarization in 7.5 M NaOH with 0.1 M H ２ SO ４ Pt recorded in ３ Cyclic voltammogram of Fe(111)-Pt skin single crystal electrode. (Figure S10): Pt ３ AFM height images of the Fe(111)-Pt skin single crystal electrode surface before (B) and after 15 min of cathodic polarization (C). SEM images of platinum electrodes treated at negative potentials in 5 M LiOH, 5 M NaOH, and 5 M KOH aqueous solutions.

[0010] Hereinafter, a corrosion-resistant metal electrode and a device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the description of each embodiment, substantially the same or similar components are denoted by the same reference numerals, and redundant descriptions may be omitted.

[0011] [Corrosion-Resistant Metal Electrode] Fig. 1 is a schematic diagram illustrating an example of the configuration of a corrosion-resistant metal electrode 1. In Fig. 1, both the counter electrode CE and the working electrode WE are corrosion-resistant metal electrodes 1, but this is not limiting. Because the electrode that needs to be the corrosion-resistant metal electrode 1 is one that is negatively polarized with respect to a standard hydrogen electrode, depending on the operating conditions of the device, one of the electrodes, i.e., the counter electrode CE or the working electrode WE, may not need to be the corrosion-resistant metal electrode 1.

[0012] The corrosion-resistant metal electrode 1 is used in a device (not shown) for detecting and / or measuring a substance. The corrosion-resistant metal electrode 1 is in contact with a solution containing a cation while being negatively polarized with respect to a standard hydrogen electrode. The corrosion-resistant metal electrode 1 is made of an alloy whose main component is platinum and whose minor component is a first transition metal.

[0013] The substance can be anything contained in a solution that can be measured. Examples of such substances include nucleic acids, amino acids, peptides, proteins, antibodies, cells, sugars, carbohydrates, metals, and compounds of metal and nonmetal elements. Examples of such nonmetal compounds include hydrogen compounds, oxides, oxoacids, hydroxides, halides, sulfates, nitrates, carbonates, acetates, and metal complexes (coordination compounds). However, the substances that can be measured are not limited to those listed above.

[0014] The device may be any device that can use the corrosion-resistant metal electrode 1 as a counter electrode CE, working electrode WE, reference electrode (not shown), or the like. Examples of such devices include, but are not limited to, measurement devices that measure the type, composition, or content of a target substance by flowing the target substance, such as electrophoresis chips that use an electric field to separate and detect charged particles or molecules, biosensor devices that use electrochemical reactions to detect biological substances, and chemical sensor devices that use electrochemical reactions to detect ions or glucose. The counter electrode CE, working electrode WE, and reference electrode are preferably, but not necessarily, provided in the same chamber within the device. Both the counter electrode CE and working electrode WE are in contact with the solution flowing through them.

[0015] The counter electrode (CE) is an electrode through which a charge of the opposite polarity flows when a voltage is applied. The working electrode (WE) is an electrode used in various electrochemical measurement methods to obtain electrical signals such as current and potential related to the electrode reaction of the substance being measured. The reference electrode is an electrode used as a reference for measuring the electrode potential of another electrode.

[0016] The situation where the electrode is in contact with a solution containing cations while being negatively polarized relative to a standard hydrogen electrode is one in which the cathodic corrosion mechanism operates. The corrosion-resistant metal electrode 1 can be used in such a situation.

[0017] Examples of cations include, but are not limited to, lithium ions, sodium ions, magnesium ions, potassium ions, calcium ions, and organic ions such as tetrabutylammonium ions.

[0018] The main component refers to a component with a high content among the metal elements constituting the electrode. The secondary component refers to a component with a low content among the metal elements constituting the electrode. In this embodiment, since the main component is platinum, the content thereof may be, for example, more than 50 at %. On the other hand, since the secondary component is a first transition metal, the content thereof may be, for example, less than 50 at %. The atomic ratio of platinum to the first transition metal can be, for example, 3:1. In the examples described later, Pt ３ Me is used. Note that Me represents a first transition metal. If the platinum and first transition metal are present in equal amounts, i.e., 50 at%:50 at%, when the electrode is negatively polarized relative to a standard hydrogen electrode and comes into contact with a solution containing cations, cathode corrosion cannot be suppressed and the surface may become rough. Furthermore, nanoparticles containing the main component, the subcomponent, or both may be generated due to corrosion.

[0019] First transition metals are also called first transition elements, 3d transition metals, 3d transition elements, etc. First transition metals refer to metals in which electrons increase in the 3d orbital, located inside the outermost orbital, as the atomic number (the number of protons in the atomic nucleus) increases. Specific examples of first transition metals include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). Zinc (Zn) may also be included as a first transition metal. Of these, Ni, Co, and Fe are preferably used in this embodiment.

[0020] [Cathodic corrosion mechanism and cathodic corrosion inhibition mechanism] The cathodic corrosion mechanism and cathodic corrosion inhibition mechanism will be explained. Figure 2 is an explanatory diagram explaining the cathodic corrosion mechanism and cathodic corrosion inhibition mechanism using platinum as an example. The upper diagram of Figure 2 (the upper diagram in horizontal writing in Figure 2) is an explanatory diagram of the cathodic corrosion mechanism that occurs in a platinum electrode (therefore, the surface is platinum). The lower diagram of Figure 2 (the lower diagram in horizontal writing in Figure 2) is an explanatory diagram of the cathodic corrosion inhibition mechanism that occurs in a platinum alloy electrode (the surface of which has a Pt skin layer formed) made of platinum and a first transition metal.

[0021] (Mechanism of Cathodic Corrosion) The present inventors consider the mechanism of cathodic corrosion as follows. First, platinum is a material with a high affinity for hydrogen. Therefore, as shown in the upper diagram of Figure 2, cathodic corrosion occurs when hydrogen adsorbed by platinum and Na ＋ This occurs at a potential where the platinum is covered with cations such as (Panel (1)). At this time, hydrogen penetrates the inside and several layers of platinum hydride are formed.

[0022] At such potentials, hydrogen evolution also occurs. Under these conditions, some of the platinum dissolves and transforms into an unknown cation-stabilizing anion (panel (2)). Note that the anion may be composed of multiple platinum atoms.

[0023] Finally, the Pt anions come into contact with water and are oxidized back to atomic platinum (metallic Pt) (panel (3)). The Pt remains on the electrode surface as a soluble ternary metal hydride. This platinum either redeposits on the electrode or nucleates into nanoparticles (panel (4)). This increases the number of platinum nanoparticles in solution and roughens the surface of the platinum electrode.

[0024] (Mechanism for Inhibiting Cathodic Corrosion) The present inventors believe the mechanism for inhibiting cathodic corrosion is as follows. The alloy metals (first transition metals) used with platinum have a low tendency to be reduced or to form hydrides. Therefore, as shown in panel (1) of the lower diagram in Figure 2, the outermost monoatomic layer is a Pt layer (Pt skin layer), and a layer (first transition metal layer) containing a first transition metal with a lower affinity for hydrogen than Pt is formed on the subsurface below it. Therefore, even when the electrode is negatively polarized relative to the standard hydrogen electrode and in contact with a solution containing cations, the subsurface layer containing a first transition metal inhibits hydrogen penetration into the lattice, as shown in panel (2) of the lower diagram in Figure 2. As a result, cathodic corrosion is inhibited.

[0025] 3 is a schematic diagram illustrating an example of the configuration of the surface of the corrosion-resistant metal electrode 1. As shown in FIG. 3, in this embodiment, it is preferable that the atomic ratio of platinum contained in the outermost monoatomic layer 1a of the alloy is greater than the atomic ratio of platinum contained in the entire corrosion-resistant metal electrode 1. In this way, the atomic ratio of platinum contained in the outermost monoatomic layer 1a of the corrosion-resistant metal electrode 1 is greater than that in the interior, and therefore hydrogen penetration into the interior can be inhibited.

[0026] Furthermore, as shown in FIG. 3 , in this embodiment, the atomic ratio of platinum in the outermost monolayer 1a of the bimetal surface 1b, which is composed of platinum and a first transition metal, is preferably greater than the atomic ratio of platinum contained in the entire bimetal surface 1b. The bimetal surface 1b refers to a region present on the surface of the electrode that is different from the interior. For example, if the bulk composition of the corrosion-resistant metal electrode 1 is platinum:first transition metal = 3:1, the composition of the interior of the electrode is approximately platinum:first transition metal = 3:1, but there is a region within a predetermined depth from the outermost surface where the ratio is not 3:1. In this embodiment, the surface including such a region is referred to as the bimetal surface 1b. Furthermore, in this embodiment, the atomic ratio of platinum in the outermost monolayer 1a, which is the outermost layer of such a bimetal surface 1b, is greater than the atomic ratio of platinum contained in the entire bimetal surface 1b. Furthermore, as shown in FIG. 3 , the subsurface below the outermost monolayer 1a is a layer rich in the first transition metal. In this way, the corrosion-resistant metal electrode 1 has a higher atomic ratio of the first transition metal contained in the sub-surface below the outermost monoatomic layer 1a than in the interior, and therefore can inhibit hydrogen from penetrating into the interior.

[0027] The layer below the subsurface may be a bulk composition layer or a layer containing slightly more platinum, but is not limited to such a state.

[0028] Here, Fig. 4 is an explanatory diagram illustrating a possible form of the bimetal surface 1b. As shown in the left diagram of Fig. 4, a possible form is one in which the outermost monoatomic layer 1a is made of first transition metal (3d) atoms (indicated by ○), the sub-surface layer below that is made of platinum atoms (indicated by ●), and the layer below that is made of platinum atoms (indicated by ●).

[0029] Furthermore, as shown in the middle diagram of Figure 4, it is conceivable that both the outermost monoatomic layer 1a and the sub-surface layer below it are formed so as to contain a mixture of first transition metal (3d) atoms (represented by ○) and platinum atoms (represented by ●), and that the layers below that are made up of platinum atoms (represented by ●).

[0030] Furthermore, as shown in the right diagram of Figure 4, a possible configuration is one in which the outermost monoatomic layer 1a is made of platinum atoms (indicated by ●), the sub-surface layer below that is made of first transition metal (3d) atoms (indicated by ○), and the layer below that is made of platinum atoms (indicated by ●). The configuration shown in the right diagram of Figure 4 is equivalent to that shown in Figure 3.

[0031] In a literature article (Weiting Yu, Marc D. Porosoff, and Jingguang G. Chen, "Review of Pt-Based Bimetallic Catalysis: From Model Surfaces to Supported Catalysts," Chem. Rev. 2012, 112, 5780-5817), it is explained that the morphology shown on the right side of FIG. 4 has higher thermodynamic stability than the morphology shown on the left side of FIG. 4. The morphology shown on the right side of FIG. 4 is also considered to have higher thermodynamic stability than the morphology shown in the middle of FIG. 4. Although it is unclear how this influences the morphology, the corrosion-resistant metal electrode 1 can be made to have excellent corrosion resistance against the cathodic corrosion mechanism by adopting a morphology similar to the morphology shown on the right side of FIG. 4, i.e., the morphology shown in FIG. 3. Conversely, it is considered that the morphologies shown on the left and middle of FIG. 4 cannot be made to have excellent corrosion resistance against the cathodic corrosion mechanism.

[0032] The corrosion-resistant metal electrode 1 according to this embodiment can be suitably produced by a flame fusion method, as described below. The layer structure and composition of the layers according to this embodiment can be determined based on in situ surface X-ray diffraction measurement and ex situ low-energy ion scattering measurement, as described below. The layer structure and composition of the layers according to this embodiment can be determined by TEM / STEM (Transmission Electron Microscope / Scanning Transmission Electron Microscope) analysis, EDS (Energy Dispersive X-ray Spectroscopy) and / or EELS (Electron Energy Loss Spectroscopy).

[0033] In this embodiment, when polarized to −1.0 V relative to a standard hydrogen electrode, the amount of platinum eluted from the surface of the corrosion-resistant metal electrode 1 is 10 pmol / mm ２ The amount of platinum eluted under the above conditions is preferably 10 pmol / mm ２ / min or less, the amount of platinum eluted is sufficiently small. This shows that the corrosion-resistant metal electrode 1 has excellent corrosion resistance and the corrosion phenomenon is suppressed.

[0034] FIG. 5 is a graph showing the amount of Pt eluted from the surface of the corrosion-resistant metal electrode 1 when polarized to −1.0 V relative to the standard hydrogen electrode. In the graph, the vertical axis represents “pmol mm －２ min －１ ", that is, the amount of Pt eluted. As shown in FIG. 5, for PtMe (Me = Ni, Fe, Co), the amount of Pt eluted under the above conditions was 10 pmol / mm ２ In contrast, the elution amount of pure Pt (denoted as Pt in the figure) is 10 pmol / mm ２ / min or more. Pt-Pd, where Me is not a first transition metal, also has a large elution amount, about 30 pmol / mm ２ / min.

[0035] FIG. 6 shows that cathodic corrosion occurs in Pt single crystals and Pt ３ 6 is an explanatory diagram showing the influence on Ni single crystal. Here, (i) in the upper part of FIG. 6 is a photograph showing the appearance of the corrosion reaction solution of Pt single crystal. (ii) in the upper part is an SEM image of the surface of Pt single crystal after corrosion treatment. The scale bar indicates 5 μm. (iii) in the upper part is a cyclic voltammogram (CV) of Pt single crystal before and after corrosion treatment. The horizontal axis is voltage (E vs. RHE (V)), and the vertical axis is current (I (μA)). (i) in the lower part of FIG. 6 is a photograph showing the appearance of the corrosion reaction solution of Pt single crystal. ３ Photographs showing the appearance of a corrosion reaction solution of a Ni single crystal. ３ This is an SEM image of the surface of a Ni single crystal after corrosion treatment. The scale bar indicates 2 μm. (iii) in the lower row shows the Pt ３ CV of a Ni single crystal before and after corrosion treatment. The horizontal axis represents voltage (E vs. RHE (V)) and the vertical axis represents current (I (μA)).

[0036] As shown in the upper part of Figure 6 (i), the Pt single crystal turned black due to Pt nanoparticles generated by cathodic corrosion in the corrosion reaction solution. Furthermore, as shown in the upper part (ii), the surface of the Pt single crystal developed characteristic triangular irregularities and became rough. As shown in the upper part (iii), the CV of the Pt single crystal differed before and after the corrosion treatment. This suggests that its performance as an electrode differed, specifically, deteriorated. These phenomena are thought to be due to the cathodic corrosion mechanism described above.

[0037] In contrast, as shown in the lower part (i) of FIG. ３ For the Ni single crystal, the corrosion reaction solution remained transparent. ３ The surface of the Ni single crystal was smooth and not roughened. ３The CV of the Ni single crystal was almost the same before and after the corrosion treatment. This suggests that the electrode performance was the same before and after the corrosion treatment, or that there was almost no deterioration. These phenomena are thought to be due to the action of the cathodic corrosion inhibition mechanism mentioned above.

[0038] FIG. 7 shows the results of the Pt single crystal and Pt under the same conditions where cathodic corrosion occurs. ３ This is a graph comparing the amounts of Pt and Ni dissolved when a corrosion reaction was carried out on a Ni single crystal. The vertical axis represents the amount of dissolved Pt (ppb). The amount of dissolved Ni was measured by inductively coupled plasma mass spectrometry (ICP-MS). As shown in FIG. 7, Pt ３ The Ni single crystal, i.e., the Pt-Ni alloy, is protected from cathodic corrosion. The amount of Pt in the Pt-Ni alloy solution is 1 / 12.54 of that in the Pt single crystal, i.e., pure Pt, even though the current during processing is similar. The amount of Ni in the Pt-Ni alloy solution is also very small.

[0039] [Device] FIG. 8 is a schematic diagram showing the configuration of a device 10. The device 10 detects and / or measures substances. As described above, examples of such devices 10 include, but are not limited to, measurement devices that measure the content of a substance to be measured by flowing it through a flow, such as electrophoresis chips that use an electric field to separate and detect charged particles or molecules, biosensor devices that use electrochemical reactions to detect biological substances, and chemical sensor devices that use electrochemical reactions to detect ions or glucose. As shown in FIG. 8, the device 10 can use the corrosion-resistant metal electrode 1 as a counter electrode CE, a working electrode WE, a reference electrode (not shown), or the like. Similar to FIG. 1, both the counter electrode CE and the working electrode WE in FIG. 8 are corrosion-resistant metal electrodes 1, but this is not limiting. Because the corrosion-resistant metal electrode 1 must be an electrode that is negatively polarized relative to a standard hydrogen electrode, depending on the operating conditions of the device, one of the electrodes, i.e., the counter electrode CE or the working electrode WE, may not need to be the corrosion-resistant metal electrode 1. The counter electrode CE, the working electrode WE, and the reference electrode are preferably, but not limited to, provided in the same chamber 11 in the device 10. Since the device 10 includes the corrosion-resistant metal electrode 1, corrosion is suppressed for the same reason as described above.

[0040] "Protection of Ni-, Co-, and Fe-based Pt skin-forming alloy electrodes from cathodic corrosion"

[0041] (Abstract) Cathodic corrosion occurs at platinum electrodes when negative potentials are applied, leading to significant dissolution and failure of the platinum electrode in the presence of electrolyte cations. However, to date, there has been a lack of research into protective measures to prevent or slow down the corrosion process of Pt electrodes. Here, we combine electrochemical measurements with in situ atomic-scale imaging using EC-AFM to investigate the atomically defined Pt(111) and Pt(111) surfaces under cathodic corrosion. ３We were able to directly track the surface structure changes from the M(111)-Pt skin (M = Ni, Co, Fe) single crystal electrodes. The changes in the electrochemical signal and the clear surface structure changes indicate that the roughening process begins at the undercoordinated sites of the Pt(111) electrode, and 100-oriented etching pits on the 111 terrace create a triangular pattern, whereas the Pt ３ The M(111)-Pt skin (M=Co, Ni, Fe) single crystal electrodes show no etching.

[0042] (Introduction) Cathodic protection is employed as an effective strategy to prevent metal corrosion. Ａ１ However, many metals undergo severe degradation in fully negatively polarized conditions, as first reported by Fritz Haber in 1902 by the formation of "metallic dust" from cathodically polarized metals. Ａ２ Inhibiting cathodic corrosion of platinum is a particularly important issue because platinum is a popular choice as the "inert" or catalytic cathode material in many electrochemical devices, particularly electrolyzers, that catalyze reactions such as the hydrogen evolution reaction (HER). Ａ３，Ａ４，Ａ５ The widespread application of these devices is still hindered by the reactivity loss and suboptimal durability of the electrocatalysts caused by structural breakdown and / or dissolution of expensive platinum during long-term deployment.

[0043] In recent years, there has been much research into the morphological changes and etching patterns that occur during cathodic corrosion of platinum nanoparticles (Haber's "metal dust") generated at platinum electrodes or in solution, and progress in this field has been reviewed. Ａ６，Ａ７，Ａ８ Briefly, cathodic corrosion of Pt is highly sensitive to the anisotropy, i.e., facets, of the crystal, and it has been demonstrated that irreducible cations, both metallic and organic cations, play a crucial role in cathodic corrosion. A6, A9, A10, A11 More specifically, Na ＋ and NH ４ ＋ The presence of cations such as Ａ６，Ａ１２Furthermore, the surface etching process and the formation of Pt nanoparticles dissolved in solution are strongly dependent on the identity and concentration of the cations. Ａ１０，Ａ１３ Recent computational studies have demonstrated that cation-stabilized, negatively charged platinum hydride PtH ｘ ｙ－ It has been shown that these species function as key intermediates in the cathodic corrosion of Pt electrodes. A9, A10, A14, A15. A combination of X-ray spectroscopy experiments and theoretical calculations revealed that the primary platinum hydride intermediate should not only include structures with hydrogen adsorbed on the Pt surface, but also Pt subsurface hydride structures (i.e., structures containing hydrogen between the top two Pt layers on the Pt surface). Ａ１５，Ａ１６ .

[0044] Although promising insights have been gained in understanding the intermediates involved in cathodic corrosion of Pt electrodes, there has been little further exploration of ways to slow or prevent cathodic corrosion of platinum electrodes. Ａ８ In a recent review on cathodic corrosion and "how to prevent it," noted that alloying has often proven to be a successful strategy for mitigating cathodic corrosion of various metals. However, this method has primarily been applied to post-transition metals such as lead, a commonly used electrode material in reductive organic electrosynthesis, with clear counterexamples of platinum-based alloys that appear not to be protected from cathodic corrosion. A17, A18, A19 Elucidating the mechanisms by which (platinum) alloys may be protected from cathodic corrosion is clearly of great interest for their use as stable cathodes in organic electrosynthesis and electrolysis devices, as well as other electrochemical devices where the cathode may be exposed to very negative potentials.

[0045] In this study, we report the discovery that platinum is largely protected from cathodic corrosion when alloyed with the first-row transition metals iron, cobalt, and nickel, whereas no such cathodic corrosion inhibition effect is observed for PtPd alloy electrodes, etc. Cathodic corrosion experiments and subsequent characterization of PtMe (Me = Ni, Co, Fe) electrodes indicate that no significant surface etching occurs on these electrodes and no substantial dissolution of Pt or alloying elements occurs under conditions that would cause pure Pt to dissolve cathodically within minutes. ３ Based on experiments using Me(111)-Pt skin single-crystal electrodes and density functional theory calculations, we argue that the formation of a first atomic surface layer of platinum (Pt skin) on these alloys, a structural phenomenon well-known for its extensive properties as highly active fuel cell cathode catalysts, plays a key role in the protection mechanism. The corresponding excess Fe, Co, or Ni in the second layer forms an effective thermodynamic or kinetic barrier against the formation of subsurface hydrides, enhancing the resilience to cathode degradation. These new insights into the Pt degradation mechanism induced by cathodic polarization and subsequent protection strategies for Pt against cathodic corrosion are essential for improving the rational design of stable Pt-based electrode materials for use under cathodic conditions.

[0046] (Experimental Methods) (Electrodes, Electrolyte Solution, and Electrochemical Cell) In this study, custom-made Pyrex glass cells and fluorinated ethylene propylene (FEP) cells were used. The Pyrex glass cells were used for all cyclic voltammogram (CV) measurements in acidic media, and the FEP cells were used for cathodic corrosion measurements in alkaline media. ２ SO ４ The (SupraPure®, Merck) electrolyte was prepared using Milli-Q water (Millipore, resistivity ≥ 18.2 MΩ cm), and the NaOH (30 wt% solution, SupraPure, Merck) electrolyte was used directly from the bottle. Glassware was cleaned using well-established standard procedures: all cells and glassware were washed with H ２ SO ４1 g / L KMnO acidified with ４ (>99%, Merck) solution. Before use, the permanganate solution was drained and ２ SO ４ The cells and glassware were cleaned from permanganate residues by storing them in a dilute piranha solution prepared by adding ACS reagent (95-98%, Merck) and hydrogen peroxide (35%, Merck) to Milli-Q water. Finally, the piranha solution was discarded, and the glassware was boiled several times in Milli-Q water. CV measurements were performed in a Pyrex glass cell containing an electrolyte by introducing Ar into the cell to remove dissolved gases. On the other hand, cathodic corrosion experiments were performed in air. A platinum wire was used as the counter electrode in the Pyrex glass cell, a Pt flag was used as the counter electrode in the FEP cell, and an RHE (HydroFlex, Gascatel) was used as the reference electrode. The use of a platinum counter electrode does not affect the observations. Ａ１１ .

[0047] (Cathodic corrosion treatment) A constant potential of −3.0 V vs. RHE was applied to Pt and Pt alloy bead electrodes in 20 mL of 30 wt % NaOH for 15 minutes. Before and after cathodic polarization, the electrodes were immersed in 0.1 M H ２ SO ４ Scan rate 50 mVs in solution －１ The characteristic hydrogen underpotential adsorption / desorption profile was examined by cyclic voltammetry measurements to determine whether any changes in the surface structure had occurred.

[0048] H ２ SO ４The CV profile of Pt in the cathode serves as an electrochemical fingerprint of the surface, so changes in the surface structure can be identified by comparing the CV profiles obtained before and after cathodic treatment. The voltammetry of Pt alloys is not as well characterized as that of pure Pt, and the increased complexity of the system can lead to unpredictable behavior after cathodic corrosion. In this case, only qualitative information can be inferred from a comparison of the CV profiles before and after cathodic corrosion. Note that, in this specification, "after cathodic corrosion" means after the process of cathodic corrosion of pure Pt has been performed.

[0049] Microscopic Analysis of Cathodic Corrosion: Surface roughening of the bead electrode due to cathodic corrosion was analyzed using a scanning electron microscope (SEM) (Apuleo SEM, Thermo Scientific). After the corrosion experiment, the bead electrode was carefully removed from the electrochemical cell and placed in a custom-made SEM sample holder. The sample was then rinsed under a stream of ultrapure water to remove the acid from the electrode.

[0050] Sample Preparation for ICP-MS: Samples from the spent corrosion electrolyte solution were collected after cathodic corrosion treatment. 0.5 mL of sample was dissolved in 6.5 mL of 65% HNO ３ The suspension was mixed with 100% ethanol and held at 120°C for 2 hours to dissolve any Pt or alloy nanoparticles that may be present in the suspension. After this, the sample was cooled to room temperature and diluted with Milli-Q water before being sent for ICP-MS analysis. The sample was analyzed on a PerkinElmer NexION 2000.

[0051] (Preparation of Single Crystal Electrodes) Pt(111) single crystal electrodes were prepared by electrochemically dissolving the Pt(111) single crystal electrode in an electrolyte (2.5 M CaCl ２ and concentrated HCl) at 50 Hz for 124 cycles, followed by thorough rinsing with ultrapure water and several flame annealings according to the Clavier method. Ａ２７ This procedure has been shown to provide a clean surface for Pt(111) single crystal electrodes with minimal contamination.Ａ２８ . Pt ３ The M(111) (M = Co, Ni, Fe)-Pt skin single crystal electrodes were fabricated using the same procedure as previously reported. ３ M(111) (M = Co, Ni, Fe) single-crystal working electrodes were annealed by induction heating in an inert all-quartz tube filled with flowing hydrogen. This is an efficient method for building an atomically flat Pt skin surface through compositional oscillation of the outermost and second layers. A24, A25, A29, A30. Induction heating was applied via a 2.4 kW Ambrell EASY Heat Model 0224 with a Flowmax water-cooling solution. H during the annealing process ２ The flow of (Air Products, 5.7) was digitally controlled using a mass flow controller (SLA5850, Brooks).

[0052] In situ electrochemical atomic force microscopy (EC-AFM) measurements. In situ EC-AFM experiments were carried out in a home-made electrochemical AFM cell made of polychlorotrifluoroethylene (PCTFE). All cell components and the electrolyte reservoir were filled with freshly prepared piranha solution (3:1 v / v H ２ SO ４ (96%, Merck SupraPure) and H ２ O ２ After washing with 35% Merck Supra Pure water for at least 2 hours, the electrodes were rinsed at least five times with ultrapure water (Milli-Q, 18.2 MΩ cm) and boiled. A coiled platinum wire was used as the counter electrode, and a reversible hydrogen electrode (RHE, Mini Hydroflex, Gascatel) was used as the reference electrode. An Autolab PGSTAT204 potentiostat with a booster (10 A) combined with an AFM (JPK NanoWizard® 4) was used to control the electrochemical conditions during the experiments.

[0053] The AFM scan rate was 1 Hz, and all images were acquired using tapping mode to minimize damage to the electrode and AFM probe. The tip used was purchased from Bruker (SNL, resonant frequency: 65 kHz, spring constant: 0.35 N / m). CV characterization of the Pt surface after cathodic corrosion was performed in sulfuric acid solution. Prior to cathodic corrosion of the Pt electrode, the surface quality and cleanliness were checked using 0.1 M H ２ SO ４ The Pt electrode was subjected to a constant cathodic potential of −3.0 V vs. RHE in 30 wt% NaOH for various periods for comparative studies with the beaded electrode. Subsequently, the CV of the Pt electrode was measured in 0.1 M H ２ SO ４ The surface morphology was imaged by AFM for comparison. All AFM images were taken at 0.55 V in the Pt bilayer region to avoid altering the surface or damaging the AFM probe. ＲＨＥ The sample was collected at a potential of .

[0054] (Results and Discussion) Figure 9A-C (Figure M1): Pt ３ Cathodic corrosion of Ni bead electrode and Pt bead electrode. Figure 9A (Figure M1): (A) -3.0 V ＲＨＥ for 30 min, 0.1 M H in ∼7.5 M (30 wt %) NaOH ２ SO ４ The Pt before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion ３ Cyclic voltammetry of Ni bead electrodes. Pt before (B) and after (C) cathodic corrosion. ３ Corresponding SEM image of the Ni bead electrode. ＲＨＥ for 30 min, 0.1 M H in ∼7.5 M (30 wt %) NaOH ２ SO ４Figure 9C (Fig. M1): (G) Pt bead electrode and Pt ３ Ni bead electrode -3.0 V ＲＨＥ ICP-MS measurement of Pt and Ni dissolved in electrolyte solution after cathodic corrosion in ∼7.5 M (30 wt %) NaOH at 700 K for 30 min.

[0055] Figure M1 shows cathodic corrosion of a Pt bead electrode and Pt ３ This figure compares the effects of cathodic corrosion on Ni bead electrodes. These "bead" electrodes are the tips of wires. If the process of melting the wire end and then solidifying it into a spherical shape is properly carried out, a smooth single-crystal surface encompassing all possible single-crystal facets on the surface of a single spherical electrode is obtained (A20, A21, A22, A23). The inventors have previously used these spherical single-crystal bead electrodes to study the structural sensitivity of the cathodic corrosion process of Pt. Ａ１１ The fabrication of the (bimetallic) bead electrode is explained in detail in Supplementary Note 1 below. Comparing Figure M1(A) and Figure M1(D), cathodic corrosion is observed in Pt ３ While the cyclic voltammogram (CV) of the Ni bead electrode is barely affected, the Pt electrode clearly undergoes significant structural changes. Cathodic corrosion of Pt leads to the enhancement of (100) step and terrace features and the suppression of (110) step features in the CV. Ａ９，Ａ１１ Figures M1(B) and M1(C) show the Pt before and after cathodic corrosion. ３ SEM images of the Ni bead electrode are shown. There is no noticeable roughness in these images. In comparison, the pure Pt bead electrode is severely roughened (see Fig. M1(E) and Fig. M1(F), see also Fig. S1 below). Finally, ICP-MS results (Fig. M1(G)) show that cathodic corrosion of pure Pt leads to substantial dissolution of Pt in the electrolyte solution, whereas the Pt ３The Ni bead electrode shows at least an order of magnitude lower concentrations of both Pt and very little Ni in the electrolyte solution. The absence of Ni in the electrolyte eliminates the mechanism by which Ni preferentially dissolves at the cathode to prevent Pt corrosion (as a kind of "anodic protection"). ３ It is important to note that the currents during the cathodic corrosion experiments of the Ni bead electrode were very similar (see Fig. S2), so the differences in cathodic corrosion were not due to differences in the (hydrogen evolution) current or the corresponding interfacial pH between the two electrodes.

[0056] As shown in Figures S3 to S5 below, Pt ３ Co and Pt ３ Very similar results were obtained with Fe bead electrodes. Although both PtCo and PtFe were protected from cathodic corrosion, it proved impossible to avoid the accumulation of Fe (oxide) on the surface during the experiments (see Figure S4). Nevertheless, ICP-MS measurements show that Pt, Co, and Fe do not dissolve during cathodic corrosion experiments (Figure S5). Pt with Me = Ni, Co, and Fe ３ When examined as Me(111)-Pt skin single crystal electrodes, these surfaces all exhibit very similar behavior.

[0057] To investigate whether alloying protects Pt from cathodic corrosion, we performed a similar series of experiments using PtPd bead electrodes. Both electrochemical characterization and SEM imaging (Figure S6, below) and measurement of Pt and Pd in ​​solution by ICP-MS after cathodic corrosion (Figure S5, below) indicate that PtPd is not protected from cathodic corrosion. This experiment demonstrates that alloying alone cannot be considered a general method for mitigating the detrimental effects of cathodic corrosion.

[0058] Pt ３ A more detailed insight into what protects Me (Me = Ni, Co, Fe) electrodes from cathodic corrosion can be found by examining the corresponding Pt ３These results were obtained from experiments using PtMe(111) single-crystal electrodes. Such electrodes have been widely studied as model surfaces for PtMe nanoparticles that function as cathode catalysts in proton exchange membrane (PEM) fuel cells. In Supplementary Note 2 below, we discuss the properties of these Pt ３ We discuss the existing literature on cyclic voltammetry of the Me(111) single crystal surface and the corresponding blank (Fig. S7 below). Briefly, based on in situ surface X-ray diffraction measurements and ex situ low-energy ion scattering measurements, we have demonstrated that Pt ３ It has been established that Me(111) single crystal surfaces, when prepared in a hydrogen atmosphere (a typical atmosphere for pretreating Pt-based electrodes to remove surface oxides), have a unique "skin-type" surface structure. The first atomic layer consists of pure Pt, while the second subsurface layer is composed of alloying elements (particularly in the case of Ni, which is ∼52 at% Ａ２４ , Co: up to 98 at% Ａ２５ , and for Fe ∼75 at% Ａ２６ This segregated surface structure strongly suggests that Pt interacts more strongly with hydrogen than transition metal alloying elements, making it surface active under hydrogen atmosphere and reductive electrochemical conditions. Furthermore, both hydrogen and (sulfate) anions are more readily absorbed by the Pt(111) than by the pure Pt(111) single crystal electrode, as inferred from the corresponding shifts in the adsorption peak potentials. ３ Weak binding to the Me(111)-Pt skin single crystal electrode has been observed (see Figure S7, Supplementary Material 2, discussed below).

[0059] Figure 10A-D (Figure M2): Pt ３ In situ EC-AFM results of cathodic corrosion of Ni(111) and Pt(111) single crystal electrodes. Figure 10A (Fig. M2): (A) In 7.5 M (30 wt%) NaOH, -3.0 V ＲＨＥ Before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion at 0.1 MH for 1 minute. ２ SO ４ Cyclic voltammetry of a Pt(111) single crystal electrode in 7.5 M NaOH at -3.0 V (Fig. 10B). ＲＨＥ(B) AFM height images of a Pt(111) single crystal electrode before (B) and after (C) cathodic corrosion for 1 min at 0.1 MH. (D) A 1 × 1 μm area image shows a well-defined triangular etch pit in the marked dashed square in (C). (E) 0.1 MH (Fig. 10C) (Fig. M2), respectively. ２ SO ４ Before cathodic corrosion in 7.5 M (30 wt %) NaOH (dark red curve (dark gray curve in the figure)) and after cathodic corrosion in 7.5 M (30 wt %) NaOH (-3.0 V) ＲＨＥ Pt after cathodic corrosion for 15 minutes (red curve (medium gray curve in the figure)) and 30 minutes (light red curve (light gray curve in the figure)) ３ Cyclic voltammetry of a Ni(111)-Pt skin single crystal electrode. For comparison, a blank voltammogram (black curve) of a Pt(111) single crystal electrode recorded under the same conditions is shown. Figure 10D (Fig. M2): (F) Pt before cathodic corrosion and (G) after 15 and (H) 30 minutes of cathodic corrosion, respectively. ３ AFM height image of Ni(111)-Pt skin single crystal electrode.

[0060] In Figure M2, the Pt(111) electrode was used for 1 minute, and the Pt ３ Ni(111)-Pt skin electrode: 15 and 30 minutes, −3.0 V ＲＨＥ compares the effect of cathodic corrosion treatment in 7.5 M NaOH. Cathodic corrosion of Pt(111) electrodes has been extensively studied using electrochemical atomic force microscopy (EC-AFM), and a recent paper Ａ１２ Briefly, in 7.5 M NaOH, at −3.0 V ＲＨＥ Cathodic corrosion of Pt(111) at 1000 K for 1 min leads to a surface covered with triangular pits of ∼30 nm in size, as imaged by EC-AFM (Fig. M2(C) and (D)). ２ SO ４In the corresponding blank CV (Fig. M2(A)), a voltammetric peak corresponding to the (100) site was observed, consistent with the (100) site generated by the triangular pits. With increasing corrosion time, the surface becomes extensively roughened and corroded, eventually rendering the nominal (111) surface unrecognizable. Figs. M2(E)-(H) show the same experiment, but now for Pt. ３ A Ni(111)-Pt skin electrode is used. ２ SO ４ The CVs (Fig. M2(E)) taken after 15 and 30 min, respectively, show that the adsorption peaks of H and sulfate shift to more and less positive potentials, respectively, indicating their stronger adsorption. However, the H adsorption region (0.05 < E < 0.35 V) remains. ＲＨＥ ) showed no new peaks, and the surface charges corresponding to the H and sulfate peaks were below those of the well-defined Pt(111) surface (Figure S8), indicating that there was no substantial surface roughening. This lack of extensive surface roughening is confirmed by EC-AFM images. After 15 and 30 minutes of cathodic treatment, the surface resembles the untreated surface (compare Figure M2(F) with Figures M2(G) and (H)). The AFM images of the etched surface show some subtle changes compared to images of the unetched surface, including a few granular bright spots and relatively small changes near the streak step sites. The slight changes near the streak step sites may be partially due to step facets, as described in our previous work on polycrystalline Pt surfaces. Ａ１２ The deposition of trace impurities or contamination due to other factors such as bubble formation and heat generation may be responsible for the granular bright spots in Figures M2(G) and (H). However, Pt ３ The complete absence of pit-like cathodic corrosion features on the Ni(111)-Pt skin single crystal surface confirms that the surface is protected from the extensive roughening that occurs on the Pt(111) surface. ３The CV changes after cathodic treatment of the Ni(111)-Pt skin single crystal surface suggest that the surface becomes Pt-rich with increasing cathodic treatment duration (see Supplementary Note 2 below for a more detailed discussion and comparison with the literature). Clearly, prolonged cathodic treatment brings more Pt to the surface, again suggesting that Pt interacts more strongly with hydrogen than with the alloying elements.

[0061] Pt ３ Co(111)-Pt skin and Pt ３ Very similar results were obtained with the Fe(111)-Pt skin single crystal electrode. Figures S9-10, which will be described later, show the results of the 0.1 M H ２ SO ４ The blank CV and Pt ３ Co(111)-Pt skin and Pt ３ The results of in situ EC-AFM of Fe(111)-Pt skin are shown. No typical features of cathodic corrosion are observed. However, Pt ３ Corresponding to Ni(111), the CV changes slightly after cathodic corrosion, suggesting that Pt segregates to the surface under the influence of cathodic treatment. Therefore, based on the CV characterization and in situ EC-AFM studies, we hypothesized that Pt in 7.5 M NaOH ３ We conclude that strong cathodic treatment of Me(111)-Pt skin (Me = Ni, Co, Fe) single crystal electrodes does not cause large-scale surface patterning, roughening, or corrosion.

[0062] The above experimental results strongly suggest that the cathodic stability of PtMe (Me = Ni, Co, Fe) electrodes is related to the differential interaction of hydrogen with the two elements and the corresponding skin-like structure, in which the first atomic layer is composed of pure Pt and the second (subsurface) layer is enriched with alloying elements.

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Hersbach TJ, Koper MTJCOiE.Cathodic corrosion: 21st century insights into a 19th century phenomenon. 2021, 26: 100653. A8. Wirtanen T, Prenzel T, Tessonnier J-P, Waldvogel SR. Cathodic corrosion of metal electrodes-how to prevent it in electroorganic synthesis. Chemical Reviews 2021, 121(17): 10241-10270. A9. Hersbach TJ, Yanson AI, Koper M. Anisotropic etching of platinum electrodes at the onset of cathodic corrosion. Nature communications 2016, 7(1): 1-7. A10. Hersbach TJ, McCrum IT, Anastasiadou D, Wever R, Calle-Vallejo F, Koper MT. Alkali metal cation effects in structuring Pt, Rh, and Au surfaces through cathodic corrosion. ACS applied materials & interfaces 2018, 10(45): 39363-39379. A11. Arulmozhi N, Hersbach TJ, Koper M. Nanoscale morphological evolution of monocrystalline Pt surfaces during cathodic corrosion. Proceedings of the National Academy of Science; 2020; 2020. p. 32267-32277. A12. Chen X, Koper MT.In Situ EC-AFM Study of the Initial Stages of Cathodic Corrosion of Pt (111) and Polycrystalline Pt in Acid Solution. The Journal of Physical Chemistry Letters 2023, 14: 4997-5003. A13. Yanson A, Antonov P, Yanson Y, Koper M. Controlling the size of platinum nanoparticles prepared by cathodic corrosion. Electrochimica Acta 2013, 110: 796-800. A14. Evazzade I, Zagalskaya A, Alexandrov V. Revealing Elusive Intermediates of Platinum Cathodic Corrosion through DFT Simulations. The Journal of Physical Chemistry Letters 2022, 13: 3047-3052. A15. Hanselman S, Calle-Vallejo F, Koper MT. Computational description of surface hydride phases on Pt (111) electrodes. The Journal of Chemical Physics 2023, 158(1): 014703. A16. Hersbach TJ, Koper MT. Platinum Hydride Formation during Cathodic Corrosion in Aqueous Solutions, submitted. A17. Rodriguez P, Tichelaar FD, Koper MT, Yanson AI. Cathodic corrosion as a facile and effective method to prepare clean metal alloy nanoparticles.Journal of the American Chemical Society 2011, 133(44): 17626-17629. A18. Hersbach TJ, Koper MT. Cathodic corrosion: 21st century insights into a 19th century phenomenon. Current Opinion in Electrochemistry 2021, 26: 100653. A19. Hersbach TJ, Kortlever R, Lehtimaki M, Krtil P, Koper MT. Local structure and composition of PtRh nanoparticles produced through cathodic corrosion. Physical Chemistry Chemical Physics 2017, 19(16): 10301-10308. A20. Arulmozhi N, Jerkiewicz G. Design and development of instrumentations for the preparation of platinum single crystals for electrochemistry and electrocatalysis research. Part 1: semi-automated crystal growth. Electrocatalysis 2016, 7: 507-518. A21. Arulmozhi N, Jerkiewicz G. Design and development of instrumentations for the preparation of platinum single crystals for electrochemistry and electrocatalysis research. 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Atomically flat Pt skin and striking enrichment of Co in underlying alloy at Pt3Co (111) single crystal with unprecedented activity for the oxygen reduction reaction. ACS omega 2018, 3(1): 154-158. A26.Toda T, Igarashi H, Uchida H, Watanabe M. Enhancement of the electroreduction of oxygen on Pt alloys with Fe, Ni, and Co. Journal of the Electrochemical Society 1999, 146(10): 3750. A27. Clavilier J, Armand D, Sun S, Petit M. Electrochemical adsorption behaviour of platinum stepped surfaces in sulphuric acid solutions. Journal of electroanalytical chemistry and interfacial electrochemistry 1986, 205(1-2): 267-277. A28. Jacobse L, Vonk V, McCrum IT, Seitz C, Koper MT, Rost MJ, et al. Electrochemical oxidation of Pt (111) beyond the place-exchange model. Electrochimica Acta 2022: 139881. A29. Gauthier Y. Pt-metal alloy surfaces: systematic trends. Surface Review and Letters 1996, 3(05n06): 1663-1689. A30. Gauthier Y, Joly Y, Baudoing R, Rundgren J. 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[0064] Supporting Information for "Protection of Ni-, Co-, and Fe-Based Pt Skin-Forming Alloy Electrodes from Cathodic Corrosion"

[0065] (Supplementary Note 1: Preparation of Pt Alloy Bead Electrode) A spherical Pt working electrode was prepared using the flame fusion method. Ｂ１ Pt alloy beads were made by partially melting pure Pt beads and carefully introducing appropriate amounts of Ni, Co, Fe, and Pd wires into the melt (nickel wire, 0.25 mm diameter, Puratronic™, 99.994% (metal basis); cobalt wire, 0.25 mm diameter, Puratronic™, 99.995% (metal basis); iron wire, 0.25 mm diameter (0.01 in), Puratronic™, 99.995% (metal basis); palladium wire, 0.25 mm diameter (0.01 in), Premion™, 99.99% (metal basis), Thermo Scientific Chemicals). These electrodes were made of Pt ３ To achieve the Me composition, the nominal composition was prepared with 25 atomic percent of the second metal. Ni, Co, and Fe were selected as alloying elements due to their ability to form a unique structure consisting of a surface monolayer of pure Pt on a non-noble metal-rich second layer. Alternatively, Pd was used as the control alloying element due to its ability to form a homogeneous solid solution with Pt (albeit with a slight Pd enrichment in the surface layer) and its similar nobleness to Pt. Ｂ７，Ｂ８ To ensure that no contamination is introduced into the beads during the manufacturing process, the bead electrodes are filled with hot aqua regia (HNO ３ The electrodes were purified by immersion in a solution of 10 ...

[0066] Figure 11 (Fig. S1): SEM image of the surface of Pt beads after cathodic corrosion treatment under the same conditions as in Fig. M1 in the main text.

[0067] Figure 12 (Fig. S2): (A) Pt immersed in 7.5 M NaOH electrolyte solution as in Figure M1 in the main text. ３ Current-time (chronoamperometry) plots of cathodic polarization at −3.0 V for (A) Ni and (B) Pt bead electrodes. The noise in the curves and the increase in current are due to hydrogen gas evolution and bubble formation. ３ The Co bead electrode also exhibited the same properties as the Pt (A) shown in Figure S2. ３ Similar results were obtained as with the Ni bead electrode (Pt-Ni) (not shown).

[0068] Figure 13 (Figure S4): Pt ３ Cathodic corrosion of an Fe bead electrode. (A) 0.1 M H 2 O before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion in 7.5 M NaOH at −3.0 V for 30 min. ２ SO ４ Pt in ３ Cyclic voltammetry of Fe bead electrodes. Pt before (B) and after (C) cathodic corrosion. ３ Corresponding SEM image of the Fe bead electrode.

[0069] Figure S4(A) shows that the peak near 0.7 V is Fe. ２＋ Fe from seeds ３＋ However, the charge in hydrogen does not increase as extensively after cathodic corrosion, indicating that despite the apparent surface changes after treatment, there is no significant surface roughening.

[0070] Figure 14 (Fig. S5): Pt bead electrode and Pt ３ The results of ICP-MS measurement of the amount of Pt contained in the electrolyte solution collected after cathodic corrosion of an Me (Me = Fe, Co, Ni, Pd) bead electrode in 7.5 M NaOH at -3.0 V for 30 minutes.

[0071] Figure 15 (Figure S6): Pt ３ Cathodic corrosion of Pd bead electrodes. (A) 0.1 M H O before (black curve) and after (red curve (gray curve in the figure)) cathodic corrosion in ∼7.5 M (30 wt %) NaOH at −3.0 V for 30 min.２ SO ４ Pt in ３ Cyclic voltammetry of a Pd bead electrode. Pt before (B) and after (C) and (D) cathodic corrosion. ３ Corresponding SEM image of the Pd bead electrode.

[0072] (Additional information 2: Pt ３ A short literature review on the electrochemistry and in situ characterization of Me(111)-Pt skin single crystal electrodes

[0073] Figure 16 (Figure S7): Pt(111) and Pt ３ Cyclic voltammogram of Me(111)-Pt skin single crystal electrode. 0.1 M H ２ SO ４ Pt(111), Pt ３ Ni(111)-Pt skin, Pt ３ Co(111)-Pt skin and Pt ３ Cyclic voltammogram of Fe(111)-Pt skin single crystal electrode. Scan rate: 20 mVs －１ The inset shows the voltage at 0.05 to 0.35 V. ＲＨＥ 1 shows the surface coverage of underpotential deposited hydrogen (H upd ) calculated based on the CV of

[0074] In the case of platinum electrodes, the use of cyclic voltammetry, especially in the so-called "hydrogen region" in sulfuric acid, is a well-established "fingerprint" for characterizing the electrode surface structure. Ｂ９ Pt(111) and a series of Pt ３ Cyclic voltammetry of Me(111)-Pt skin (Me = Ni, Co, Fe) single crystal electrodes was first performed in 0.1 M H ２ SO ４ Medium, 20mVs －１ B4, B10, B11, B12, and B13 were performed at a scan rate of 1000 s. Figure S7 shows the voltammogram characteristics of the blank Pt(111) electrode (black curve): approximately 160 μC cm －２ 111 terraces with a total charge of 0.05<E<0.35V ＲＨＥThe extensive underpotential deposited hydrogen on the Pt(111) electrode is characterized by a 2 / 3 monolayer (θ Ｈｕｐｄ ) resulting from the adsorption of one monovalent adsorbate per surface atom in 1 ML, i.e., 1.5 × 10 １５ atomic cm －２ is exactly 240 μC cm －２ This is 0.05 to 0.35V ＲＨＥ is obtained by integrating the anodic double layer corrected current between (black shading, Figure S7); approximately 80 μC cm －２ 0.35 to 0.60 V with a total charge of ＲＨＥ The “butterfly” feature of (bi)sulfate adsorption / desorption (gray shading, Figure S7) between 0.50 V ＲＨＥ The sharp peak observed at is due to the (bis)sulfate adsorption layer. Ｂ１４ This arises from the order-disorder transition of Pt and occurs only on wide, well-prepared 111 terraces with very low step density. ３ Ni(111)-Pt skin (red curve (dark gray curve in the figure)), Pt ３ Co(111)-Pt skin (green curve (middle gray curve in the figure)) and Pt ３ We show well-characterized cyclic voltammograms for Fe(111)-Pt skin (yellow curve (light gray curve in the figure)) single crystal electrodes, and our results are consistent with published studies. B4, B10, B11, B12, B13: 0.05<E<0.35V ＲＨＥ The underpotential deposited hydrogen (θ Ｈｕｐｄ ), the (bis)sulfate adsorption / desorption region is suppressed, and all three Pt ３ Approximately E>0.50 V against Me(111)-Pt skin (Me=Ni, Co, Fe) single crystal electrodes ＲＨＥ The potential shifted to a higher potential. ３ Careful previous studies on Me(111)-Pt skin (Me = Ni, Co, Fe) single crystal electrodes have shown that while the Pt skin is composed of the same surface density of Pt atoms as Pt(111), it exhibits a large downward shift in the d-band center position, i.e., Pt ３0.34 eV for the Co(111)-Pt skin surface (the lattice distance was reduced due to the difference in atomic size between the top Pt layer and the subsurface alloying elements) was found to change the potential-dependent surface coverage of adsorbed species B4, B10, B15.

[0075] Figure 17 (Figure S8): Pt ３ Cyclic voltammograms of the Ni(111)-Pt skin single crystal electrode were taken in 7.5 M NaOH at −3.0 V for 15 min (red curve) and 30 min (light red curve) at 0.1 M H before (dark red curve) and after cathodic polarization at −3.0 V. ２ SO ４ The scan rate was 20 mV / s. The lower panel shows the voltages from 0.05 to 0.35 V, respectively. ＲＨＥ and 0.35 to 0.85V ＲＨＥ Hupd (θ) calculated based on CV from Ｈｕｐｄ ) and (bis)sulfate adsorption charge (Q （Ｈ）ＳＯ４ ) surface coverage. For comparison, a blank voltammogram of Pt(111) (black curve) recorded under the same conditions is shown.

[0076] Figure S8 shows Pt ３ Hupd region of Ni(111)-Pt skin single crystal electrode (0.05<E<0.35V ＲＨＥ ) increases from 0.40 ML (dark red) to 0.46 ML (red) and 0.62 ML (light red) with increasing cathodic polarization time to 15 and 30 min, respectively. ３ (Bi)sulfate adsorption on Ni(111)-Pt skin single crystal electrodes was observed at more negative potentials (E > 0.35 V ＲＨＥ ) and the charge significantly increases with increasing cathodic polarization at 15 and 30 minutes, respectively. ３This may be related to the change in alloy composition in the subsurface layer of the Ni(111)-Pt skin single crystal electrode. ｘ Me ｙ The sequential changes of cyclic voltammograms of (111)-Pt skin (Me = Ni, Co, Fe) single crystal electrodes show the influence of Hupd region and (bis)sulfate adsorption process. Ｂ５，Ｂ６，Ｂ１６ . Pt ｘ Me ｙ The charge on the Hupd and (bisulfate) regions of the (111)-Pt skin (Me = Ni, Co, Fe) single crystal electrode increased, and the butterfly-like wave shifted to more negative potentials with decreasing Me content. Ｂ５，Ｂ６，Ｂ１６ , i.e., approaching bare Pt(111), similar to those obtained in Figures S8, S9, and S10.

[0077] Figure 18A, B (Figure S9): Pt during cathodic corrosion ３ In situ EC-AFM results of Co(111)-Pt skin single crystal electrodes. Figure 18A (Figure S9): (A) Pt ３ The cyclic voltammogram of the Co(111)-Pt skin single crystal electrode was measured in 7.5 M NaOH at −3.0 V. ＲＨＥ 0.1 MH before (dark green curve) and after cathodic polarization for 15 minutes (green curve) and 30 minutes (light green curve) ２ SO ４ The scan rate was 20 mV / s. The lower panel shows the voltages from 0.05 to 0.35 V, respectively. ＲＨＥ and 0.35 to 0.85V ＲＨＥ Hupd (θ) calculated based on CV from Ｈｕｐｄ ) and (bis)sulfate adsorption charge (Q （Ｈ）ＳＯ４ ) are shown. For comparison, blank voltammograms of Pt(111) (black curve) recorded under the same conditions are shown. Figure 18B (Figure S9): Pt ３Corresponding AFM height images of the Co(111)-Pt skin single crystal electrode surface before (B), (D) and after (C) 15 min and (E) 30 min of cathodic polarization.

[0078] Figure 19A, B (Figure S10): Pt during cathodic corrosion ３ In situ EC-AFM results of Fe(111)-Pt skin single crystal electrodes. Figure 19A (Figure S10): (A) Pt ３ Cyclic voltammograms of the Fe(111)-Pt skin single crystal electrode were obtained before (brown curve (gray curve in the figure)) and after (yellow curve (light gray curve in the figure)) cathodic polarization at −3.0 V for 15 min in 7.5 M NaOH with 0.1 M H ２ SO ４ The scan rate was 20 mV / s. The lower panel shows the voltages from 0.05 to 0.35 V, respectively. ＲＨＥ and 0.35 to 0.85V ＲＨＥ Hupd (θ) calculated based on CV from Ｈｕｐｄ ) and (bis)sulfate adsorption charge (Q （Ｈ）ＳＯ４ ) surface coverage. For comparison, a blank voltammogram of Pt(111) (black curve) recorded under the same conditions is shown. Figure 19B (Figure S10): Pt ３ AFM height images of the Fe(111)-Pt skin single crystal electrode surface before (B) and after 15 min of cathodic polarization (C).

[0079] (References in the support information) B1. Arulmozhi N, Jerkiewicz G. Design and development of instrumentations for the preparation of platinum single crystals for electrochemistry and electrocatalysis research. Part 1: semi-automated crystal growth. Electrocatalysis 2016, 7: 507-518. B2. van der Vliet DF, Wang C, Li D, Paulikas AP, Greeley J, Rankin RB, et al. Unique electrochemical adsorption properties of Pt‐skin surfaces. Angewandte Chemie International Edition 2012, 51(13): 3139-3142. B3. Wadayama T, Todoroki N, Yamada Y, Sugawara T, Miyamoto K, Iijama Y. Oxygen reduction reaction activities of Ni / Pt (111) model catalysts fabricated by molecular beam epitaxy. Electrochemistry communications 2010, 12(8): 1112-1115. B4. Kobayashi S, Aoki M, Wakisaka M, Kawamoto T, Shirasaka R, Suda K, et al. Atomically flat Pt skin and striking enrichment of Co in underlying alloy at Pt3Co (111) single crystal with unprecedented activity for the oxygen reduction reaction. ACS omega 2018, 3(1): 154-158. B5.Wakisaka M, Kobayashi S, Morishima S, Hyuga Y, Tryk D, Watanabe M, et al. Unprecedented dependence of the oxygen reduction activity on Co content at Pt Skin / Pt-Co (111) single crystal electrodes. Electrochemistry Communications 2016, 67: 47-50. B6. Wakisaka M, Hyuga Y, Abe K, Uchida H, Watanabe M. Facile preparation and electrochemical behavior of Pt100- xCox (111) single-crystal electrodes in 0.1 M HClO4. Electrochemistry communications 2011, 13(4): 317-320. B7. Schmidt T, Markovic N, Stamenkovic V, Ross P, Attard G, Watson D. Surface Characterization and Electrochemical Behavior of Well-Defined Pt- Pd {111} Single-Crystal Surfaces: A Comparative Study Using Pt {111} and Palladium-Modified Pt {111} Electrodes. Langmuir 2002, 18(18): 6969-6975. B8. Watson D, Attard G. Surface segregation and reconstructive behaviour of the (1 0 0) and (1 1 0) surfaces of platinum-palladium bulk alloy single crystals: a voltammetric and LEED / AES study. Surface science 2002, 515(1): 87-93. B9.Solla-Gullon J, Rodriguez P, Herrero E, Aldaz A, Feliu JM. Surface characterization of platinum electrodes. Physical Chemistry Chemical Physics 2008, 10(10): 1359-1373. B10. Stamenkovic VR, Fowler B, Mun BS, Wang G, Ross PN, Lucas CA, et al. Improved oxygen reduction activity on Pt3Ni (111) via increased surface site availability. science 2007, 315(5811): 493-497. B11. Stamenkovic VR, Mun BS, Mayrhofer KJ, Ross PN, Markovic NM. Effect of surface composition on electronic structure, stability, and electrocatalytic properties of Pt-transition metal alloys: Pt-skin versus Pt-skeleton surfaces. Journal of the American Chemical Society 2006, 128(27): 8813-8819. B12. Kobayashi S, Aoki M, Wakisaka M, Kawamoto T, Shirasaka R, Suda K, et al. Surface X-Ray Scattering on Pt-skin / Pt3Co (111) Single-Crystal Electrode Highly Activity for the Oxygen Reduction Reaction. B13. Suzuki A, Nakamura M, Hoshi N. Structural effects of the oxygen reduction reaction on the high index planes of Pt3Fe.Electrochemistry Communications 2022, 136: 107235. B14. Koper MT, Lukkien JJ. Modeling the butterfly: influence of lateral interactions and adsorption geometry on the voltammetry at (111) and (100) electrodes. Surface science 2002, 498(1-2): 105-115. B15. Kitchin J, Norskov JK, Barteau M, Chen J. Modification of the surface electronic and chemical properties of Pt (111) by subsurface 3d transition metals. The Journal of chemical physics 2004, 120(21): 10240-10246. B16. Wakisaka M, Morishima S, Hyuga Y, Uchida H, Watanabe M. Electrochemical behavior of Pt-Co(111), (100) and (110) alloy single-crystal electrodes in 0.1 M HClO 4 and 0.05 M H 2SO 4 solution as a function of Co content(Article). Electrochemistry Communications 2012, Vol.18(No.1): 55-57. .

[0080] The corrosion-resistant metal electrode 1 and device 10 according to the present invention have been described in detail above through embodiments and examples. However, the present invention is not limited to the above-described embodiments and examples, and various modifications are included. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0081] REFERENCE SIGNS LIST 1 corrosion-resistant metal electrode 1a outermost monoatomic layer 1b bimetal surface 10 device 11 chamber CE counter electrode WE working electrode

Claims

1. A corrosion-resistant metal electrode used in a device for detecting and / or measuring substances, which is in contact with a solution containing cations while being negatively polarized relative to a standard hydrogen electrode, and which is made of an alloy whose main component is platinum and whose secondary component is a first transition metal.

2. The corrosion-resistant metal electrode according to claim 1, wherein the atomic ratio of platinum contained in the outermost monoatomic layer of said alloy is greater than the atomic ratio of platinum contained in the entire corrosion-resistant metal electrode.

3. The corrosion-resistant metal electrode according to claim 1, wherein the atomic ratio of platinum in the outermost monoatomic layer of the bimetal surface consisting of platinum and the first transition metal is greater than the atomic ratio of platinum contained in the entire bimetal surface.

4. The corrosion-resistant metal electrode according to claim 1, wherein the outermost monoatomic layer of the alloy is a platinum layer, and the layer below the outermost monoatomic layer is a first transition metal layer containing a first transition metal in greater amounts than platinum.

5. The corrosion-resistant metal electrode of claim 4, wherein the layer below the first transition metal layer is a platinum layer.

6. When polarized to -1.0 V relative to a standard hydrogen electrode, the amount of platinum eluted from the surface of the corrosion-resistant metal electrode is 10 pmol / mm ２ 2. The corrosion-resistant metal electrode according to claim 1, wherein the corrosion resistance is 0.1% or less.

7. A device comprising the corrosion-resistant metal electrode according to any one of claims 1 to 6.

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