JP5207461B2 - Electrocatalyst and electrode using the same - Google Patents

Description

  The present invention relates to an electrocatalyst suitable for use as an electrode for, for example, water or organic electrolysis, a fuel cell, and an electrode using the same.

Since noble metals such as platinum are stable even at high potentials and have high catalytic ability, they are used as catalysts for electrodes in various electrochemical systems. However, since the price of platinum is high and the amount of resources is limited, a highly active catalyst that can replace platinum is desired.
Therefore, molybdenum nitride as a transition metal (see, for example, Patent Document 1), and a mixture of iron nitride as a transition metal and a noble metal (see, for example, Patent Document 2) are used as electrode catalysts. Has been advocated.
Furthermore, an electrode catalyst made of oxynitride containing Zr is disclosed (for example, see Patent Document 3), and this electrode does not dissolve even when used at a potential of 0.4 V or higher with respect to the reversible hydrogen electrode potential in an acidic electrolyte. It is reported to have corrosion resistance.

JP 2005-63677 A JP 2005-44659 A Japanese Patent Laid-Open No. 2005-161203

However, in the case of the techniques described in Patent Documents 1 and 2, the oxygen reducing ability in the acidic electrolyte is insufficient, and the catalyst may be actively dissolved.
In the technique described in Patent Document 3, when complete ZrO _1/2 N is used as the oxynitride of Zr, this composition shows a semiconductor and is poor in catalytic activity, so that it is difficult to use as an electrode.
Accordingly, an object of the present invention is to provide an electrode catalyst excellent in catalytic ability and stability using ZrO _1/2 N and an electrode using the same.

The electrode catalyst of the present invention has a crystal structure by X-ray diffraction of ZrO _1/2 N, and an oxygen reduction current flows when the potential is scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. The starting potential is 0.75 V or more on the basis of the reversible hydrogen electrode potential.

  The ionization potential is preferably 5.4 eV or less.

  The electrode of the present invention is characterized by carrying fine particles of the electrode catalyst.

According to the present invention, an electrode catalyst excellent in catalytic ability and stability and an electrode using the same can be obtained using ZrO _1/2 N.

Hereinafter, embodiments of the present invention will be described. Note that the potential used in the following description and chart is based on the reversible hydrogen electrode potential reference, and this is expressed as RHE.
<Zr oxynitride used for electrode>
The electrode catalyst of the present invention is a zirconium oxynitride whose crystal structure by X-ray diffraction is ZrO _1/2 N.
Zirconium oxynitride is represented by ZrO _x N _y . ZrO _11/7 N _2/7 , ZrO _8/7 N _4/7 and ZrO _1/2 N are known as zirconium oxynitrides. However, in order for the oxygen reduction starting potential described later to be 0.75 V or more, It is necessary to be close to ZrO _1/2 N. More preferably, x <8/7 and y> 4/7. When x is 8/7 or more and y is less than 4/7, the degree of nitridation is not sufficient, and the electronic state of the above elements may change, thereby reducing the catalytic ability.

However, since the composition completely showing ZrO _1/2 N is a semiconductor and has poor catalytic activity, it cannot be used as an electrode. In order to put it into practical use as an electrode, the oxygen reduction starting potential needs to be 0.75 V or more.
The oxygen reduction starting potential is defined as follows. First, when a potential scan is performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., the difference between the measured current values in an oxygen atmosphere and a nitrogen atmosphere is converted into a current density on the basis of the geometric area. _{Let O2} . The potential when i _O2 is −0.1 μA cm ⁻² is expressed as an oxygen reduction start potential E _ORR, and E _ORR needs to be 0.75 V or more with respect to the reversible hydrogen electrode potential.
The oxygen reduction starting potential is an evaluation of the oxygen reduction current per unit amount of the catalyst, and the activation energy of the reaction may be smaller as the oxygen reduction current starts to flow from a higher potential. This is because the reduction current value can be increased by engineering improvement of increasing the surface area.
The reason why the oxygen reduction start potential E _{ORR is set} to 0.75 V or more is that when considering the operating voltage of the fuel cell, it is not practical as an electrode unless it is 0.75 V or more. If the oxygen reduction starting potential is 0.75 or more, it has sufficient oxygen reducing ability.

The present inventors have found that oxygen defects should be present on the surface of ZrO _1/2 N in order to make the oxygen reduction start potential of ZrO _1/2 N be 0.75 V or more.
Here, the ionization potential of the oxide is reduced by nitriding. For example, the literature value of the ionization potential of ZrO ₂ is 7.4 eV (JW Schultze and AW Hassel, p.234, in Encyclopedia of Electrochemistry Vol.4, Edited by AJ Bard and M. Stratmann, Wiley-VCH GmbH & Co. KGaA, Weinheim, (2003)). On the other hand, the literature value of the ionization potential of complete ZrO _1/2 N is at least 5.6 eV or more (T. Mishima, M. Matsuda, and M. Miyake, Appl. Catal A: Gen, 324, 77 (2007)). Nitriding reduces the ionization potential.
Furthermore, it is known that oxygen defects on the oxide surface generally reduce the ionization potential and make it closer to the metal (VE Henrich et al., Phys. Rev. Lett., 36, 1335 (1976).). In addition, it has been clarified that oxygen defects are necessary for the adsorption of oxygen molecules on the oxide surface (J.-M. Pan et al., J. Vac. Sci. Technol. A, 10, 2470 (1992), AL Lisebigler et al., Chem. Rev., 95, 735 (1995), C. Descorme et al., J. Catal., 196, 167 (2000)).

Based on the above knowledge, since the oxygen reduction reaction starts by adsorption of oxygen molecules, the present inventors have found that it is necessary to improve the oxygen reduction catalytic ability to create a state having oxygen defects on the surface. Found. Since the ionization potential decreases with an increase in oxygen defects, the catalytic activity is improved if the ionization potential is lower than the complete ionization potential of ZrO _1/2 N (5.6 eV or more) (on the crystal structure).

  The Zr oxynitride is preferably crystallized. The reason for this is considered to be that crystallization increases the conductivity and changes the electronic state of the element to improve the catalytic activity.

<Production of Zr oxynitride>
The Zr oxynitride that is an electrode catalyst can be produced, for example, as follows. A Zr oxide is used as a starting metal compound, and this is reacted with a nitrogen-containing compound such as ammonia, ammonium salt, hydrazine, nitrogen, metal nitride, metal amide, metal ammine complex or the like. For example, the reaction may be performed by heating a powdery mixture of a raw material Zr oxide and a nitrogen-containing compound or oxidizing a surface of a Zr metal plate to form a raw material Zr oxide, which is then nitrided with nitrogen or a nitrogen-containing compound. For example, a method of partially nitriding only the surface can be appropriately employed.

  When using a Zr metal salt or Zr metal complex as a raw material, before nitriding, for example, the Zr metal salt or Zr metal complex is dissolved in an organic solvent such as alcohol and then heat-treated in the atmosphere at a temperature of 923 K for 2 hours. By using this method, a metal oxide as a precursor may be formed and used.

  When powder is used as the raw material metal compound, the size of the obtained metal oxynitride fine particles is almost determined by the size of the raw material powder, so fine particles having a desired size can be obtained by adjusting the size of the raw material powder. Can do.

  The reaction temperature with the nitrogen-containing compound is preferably in the range of 973 to 2073K. If the temperature is lower than 973 K, the reaction rate is slow and the reaction may not proceed. When the reaction temperature is higher than 2073 K, the product is decomposed and does not become oxynitride.

Zr oxynitride can be manufactured using reactive sputtering. For example, glassy carbon, carbon powder, Ti, or the like can be used as a base material, and a thin film of ZrO _x N _y nitride can be formed by sputtering as an electrode material. The sputtering conditions can be, for example, Ar partial pressure of about 9 × 10 ⁻² Pa, nitrogen partial pressure of about 4 × 10 ⁻¹ Pa, oxygen partial pressure of about 2 × 10 ⁻³ Pa, and Zr can be used as a target.

<Oxygen defect formation>
As described above, perfect ZrO _1/2 N is a semiconductor and has low catalytic activity. For example, when manufacturing a Zr oxynitride, if the nitridation is allowed to proceed completely, it becomes a complete nitride. Therefore, in order for oxygen defects to exist in ZrO _1/2 N, it is necessary to control the degree of nitriding.

  In order to control the degree of nitridation, it is advantageous to employ a reaction between a metal oxide and ammonia. In this reaction, oxygen is removed with the progress of nitriding, so ammonia becomes a reducing agent and a nitriding agent. The degree of nitridation can be controlled by changing the supply rate of ammonia and the reaction temperature. At this time, by adding water vapor and nitrogen to ammonia to make a mixed gas and changing the partial pressure of ammonia, the nitriding rate is reduced, the difference in the degree of nitriding depending on the position of the electrode catalyst is reduced, and the uniformly nitrided oxy It becomes easy to obtain a nitride.

In addition, when Zr oxynitride is produced using a reactive sputtering method, oxygen defects can be present by heating the substrate during sputtering.
The sputtering method forms a film by striking a target with a plasma gas in a high vacuum, so that a reduced film is easily formed essentially. For example, in the case of an oxide thin film, the reduced state film has a composition of ZrO2-x instead of ZrO2, and Zr is +3 instead of +4. It means that there is a defect. Therefore, oxygen defects are inherently likely to be generated by sputtering. Furthermore, when the substrate is heated, a compound is formed while performing intense thermal motion, so that the amount of lattice defects generated increases. This is because a structure having defects is more stable than a regular structure having no defects in view of entropy. As a result, oxygen defects also increase.

  When the above-mentioned Zr oxynitride is used as an electrode catalyst for an oxygen reduction electrode, the oxynitride does not dissolve and is stable even when used in an acidic electrolyte, and the oxygen reducing ability and stability in the acidic electrolyte are further improved. Are better.

<Manufacture of electrodes>
An electrode can be manufactured as follows, for example. First, the above-mentioned Zr oxynitride powder is mixed with a powder of a conductive material such as tungsten oxide, iridium oxide or the like, and mixed with a known binder to form a paste. The electrode is manufactured by applying and drying.
For example, as an electrode for a fuel cell, it is preferable to use carbon black as the conductive powder, and to have a particle size of the above-mentioned nitride fine particles of about 2 to 3 nm because the catalytic ability can be exhibited even with a small amount of catalyst.

  The electrode of the present invention can be suitably used as an electrode for a cathode of an electrochemical system using an acidic electrolyte such as water, an inorganic substance, an organic substance, or a fuel cell. The electrode of the present invention is suitable as an oxidizer electrode when an acidic electrolyte is used, such as a phosphoric acid fuel cell and a polymer electrolyte fuel cell.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Creation of electrode>
A cylindrical glassy carbon having a diameter of 5.2 mm was used as a base material, and a ZrO _x N _y nitride thin film as an electrode material was formed on the bottom by sputtering. The sputtering conditions were Ar partial pressure of about 9 × 10 ⁻² Pa, nitrogen partial pressure of about 4 × 10 ⁻¹ Pa, oxygen partial pressure of about 2 × 10 ⁻³ Pa, and the target was Zr. The substrate was heated during sputtering.

  The obtained thin film was processed by FIB (Focused Ion Beam), and the cross section was observed by TEM (Transmission Electron Microscope).

FIG. 1 shows a cross-sectional TEM image of the electrode thin film when the substrate is heated and sputtered at 800 ° C. The thin film was uniformly formed with a thickness of about 70 nm, and a crystal phase was observed in the film.
The result of measuring the crystal structure of the thin film of FIG. 1 with a thin film X-ray diffractometer is shown in FIG. The diffraction peak was identified as Zr ₂ ON ₂ (JCPDS 50-1170). JCPDS (Joint Committee on Powder Diffraction Standards) is a card number assigned by an organization creating a database relating to X-ray diffraction.

<Comparative Examples 2 and 3>
As Comparative Examples 2 and 3, electrodes were prepared in the same manner as in Example 1 except that the substrate heating temperature during sputtering was set to 70 ° C. and 500 ° C., respectively, and measurements were performed in the same manner.
3 and 4 show cross-sectional TEM images of the electrode materials of Comparative Examples 2 and 3, respectively. 3 and 4, it was found that the thin films were uniformly formed with a thickness of about 50 to 70 nm.
FIG. 5 shows the results of measuring the crystal structure of the thin films of Comparative Examples 2 and 3 with a thin film X-ray diffractometer. In the case of Comparative Example 2 (substrate temperature 70 ° C.), the crystal structure was identified as ZrO ₂ (JCPDS 50-1089) from the diffraction peak. In the case of Comparative Example 3 (substrate temperature 500 ° C.), the crystal structure was identified as Zr ₇ O ₈ N ₄ (JCPDS 50-1172) from the diffraction peak.

<Evaluation>

<Evaluation of electrochemical stability of oxygen reduction electrode>
The current-potential curve (cyclic voltammogram: CV) of the electrode using the electrode material of Example 1 was measured. CV was performed using the above electrode as a cathode, a platinum foil as a counter electrode, and scanning at 50 mV / s at a potential between 0.05 V and 1.0 V at 30 ° C. in a nitrogen atmosphere. As an electrolyte, a 0.1 mol / L sulfuric acid aqueous solution was used.
The results are shown in FIG. The shape of CV shows the charge / discharge current of a typical capacitor, but the shape of CV did not change even when the potential scan was repeated several tens of times, and no oxidation current or reduction current based on the reaction was observed. Therefore, this electrode was found to be extremely stable in the range of 0.05 to 1.0 V in sulfuric acid (acidic electrolyte).

<Measurement of reduction current>
In the above electrolytic cell, a carbon plate is used as a counter electrode, a reversible hydrogen electrode having a sulfuric acid concentration of 0.1 mol / L is used as a reference electrode, and 0.05 to 1.0 at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. When the potential was scanned with V, the difference between the current values in the oxygen atmosphere and the nitrogen atmosphere was converted into a current density on the basis of the geometric area to obtain _iO2 . The potential when i _O2 was −0.1 μA cm ⁻² was determined as the oxygen reduction starting potential E _ORR .
A Tafel plot of the obtained current-potential curve is shown in FIG. The higher the oxygen reduction starting potential, the higher the catalytic ability. In the case of Example 1, E _ORR was 0.75 V or more, but in Comparative Examples 2 and 3, E _ORR was less than 0.75 V. Further, comparing Comparative Examples 2 and 3, it was found that the ionization potential was reduced in Comparative Example 3 containing nitrogen.
Incidentally, literature values of the ionization energy of ZrO ₂ has been already described If it is 7.4 eV, the ionization energy of the sample of Comparative Example 2 which corresponds to the composition is lower than this (about 5.2 eV). This suggests that the ionization potential differs depending not only on the structure identified by X-rays but also on the oxygen defects present on the surface. For example, in the case of Comparative Example 2, since the substrate temperature during film formation is low, the reactivity with oxygen is not high, and it is considered that the amorphous phase increases and defects increase.
As is apparent from FIG. 7, in the case of Comparative Example 2 (ZrO _x N _y x = 2 and y = 0) and Comparative Example 3 (ZrO _x N _y x = 8/7 and y = 4/7), In either case, E _ORR was less than 0.75 V. In particular, in the case of Comparative Example 3, even if it was Zr oxynitride, E _ORR did not become 0.75 V or more. This shows that the composition of the electrode catalyst is preferably close to ZrO _1/2 N, and x> 8/7 and y> 4/7.

The ionization potential of each electrode sample was measured in the atmosphere using a photoelectron spectrometer AC-2 (manufactured by Riken Keiki).
However, points other than Example 1 and Comparative Examples 2 and 3 were produced by changing the substrate temperature during sputtering, but the composition was not measured.

<Creation of electrode>
A cylindrical glassy carbon having a diameter of 5.2 mm was used as a base material, and a ZrO _x N _y nitride thin film as an electrode material was formed on the bottom by sputtering. In order to investigate the influence of the gas atmosphere during sputtering, the substrate temperature was fixed at 800 ° C, and the N ₂ flow rate was set to 0, 10, 24, 29 cm ³ min ^-1 (0 ° C, converted to 1.013 × 10 ⁶ Pa) Under the respective N ₂ flow rates, films were formed under the conditions of O ₂ flow rates of 0.01, 0.05, 0.10, 0.15, and 0.30 cm ³ min ⁻¹ , respectively. The Ar flow rate was controlled so that the flow rate sum with N ₂ was 29 cm ³ min ⁻¹ . The total pressure in the chamber was measured each time and was approximately 5.0 × 10 ⁻¹ Pa. N ₂ and O ₂ partial pressures were calculated from the flow rate and the total pressure in the chamber. The film formation time was all 80 minutes and the sputtering output was 150 W.

FIG. 8 shows current-potential curves of the oxygen reduction reaction of ZrO _x N _y produced in some typical gas atmospheres. Example 2 shown in FIG. 8 is a case where N ₂ and O ₂ are appropriately contained (P _Ar = 0.089 Pa, P _N2 = 0.41 Pa, and P _O2 = 1.7 mPa; P _N2 / P _O2 = 240). . In Comparative Example 4 shown in FIG. 8, the flow rate of O ₂ is 1/10 compared to Example 2 (P _Ar = 0.090 Pa, P _N2 = 0.41 Pa, and P _O2 = 0.17 mPa; P _N2 / P _O2 = 2400). Comparative Example 5 shown in FIG. 8 is a case where only Ar and O ₂ not containing N ₂ are used.
In Example 2, i _ORR is observed from 0.8 V, indicating that it has a high oxygen reduction catalytic ability. In Comparative Example 4 in which P _N2 / P _O2 was an order of magnitude larger than that in Example 2, the catalytic ability was reduced as compared with Example 2. Further, in Comparative Example 5 was prepared in an atmosphere that does not contain N _2, catalytic activity was found to be very low.
From these facts, it can be seen that even when the substrate is heated to 800 ° C., the gas atmosphere during sputtering greatly affects the oxygen reduction catalytic ability. Furthermore, since Comparative Example 5 had the highest activity, it was considered that high oxygen reduction activity could be obtained by sputtering in an atmosphere containing moderate N ₂ and O ₂ . Therefore, in order to investigate the influence of the gas atmosphere in more detail, the dependency of the oxygen reduction starting potential E _{ORR on} the O ₂ partial pressure P _O2 and the N ₂ partial pressure P _N2 was examined as follows.

FIG. 9 shows the relationship between E _ORR and P _O2 when the N ₂ flow rate is 10, 24, and 29 cm ³ min ⁻¹ . Under this N ₂ flow rate, the E _ORR reached a maximum of 0.78 V when the O ₂ partial pressure was 2 mPa. That is, it can be said that sputtering under an appropriate O ₂ partial pressure greatly contributes to the improvement of oxygen reduction activity.
FIG. 10 shows the relationship between E _ORR and P _N2 when the O ₂ flow rate is changed from 0.01 to 0.30 cm ³ min ⁻¹ . The E _ORR when N ₂ is not included in the sputtering gas is as low as 0.2 to 0.5 V. Therefore, it can be seen that it is necessary for oxygen reduction catalytic ability to contain N ₂ in the gas during sputtering. In addition, when P _N2 is 0.2 Pa or more, E _ORR becomes 0.7 V and hardly _{changes.Therefore} , the presence of N ₂ is necessary, but under this production condition, N ₂ partial pressure is not so much for oxygen reduction catalytic ability. It can be seen that there is no effect, and it is sufficient that the atmosphere during sputtering contains some N ₂ .
From the above, it was found that it is important for the gas during sputtering to contain N ₂ and appropriate O ₂ in order for the thin film catalyst produced by the reactive sputtering method to have high oxygen reduction catalytic ability. This result indicates that zirconium nitridation and moderate oxidation may be important.

FIG. 11 shows the thin film X-ray diffraction patterns of the catalysts prepared under the conditions shown in FIG.
In FIG. 11, formation of Zr ₂ ON ₂ was confirmed in Example 2, which is the most active. Further, in Comparative Example 4 having a slightly low catalytic ability, the formation of Zr ₇ O ₈ N ₄ was observed simultaneously with the formation of Zr ₇ O ₈ N ₄ due to the low O ₂ partial pressure. Further, in Comparative Example 5 with extremely low catalytic ability, a peak located between Zr and ZrO _0.35 and a ZrO peak were observed, indicating that a low-order oxide was produced.
As in the case of changing the substrate temperature shown in FIG. 7, it was found that also in the case of FIG. 11 where the gas atmosphere was changed, the catalyst having high oxygen reduction activity contained Zr ₂ ON ₂ . From these results, it is considered that having a highly crystalline Zr ₂ ON ₂ structure is necessary to have a high oxygen reduction catalytic ability.

FIG. 12 shows the relationship between ionization energy and oxygen reduction start potential of a thin film catalyst produced by changing the gas atmosphere.
As apparent from FIG. 12, in the case of Comparative Examples 2 to 5 having a catalyst structure different from that of Zr ₂ ON ₂ , an oxygen reduction starting potential exceeding 0.75 V was not obtained regardless of the ionization energy.
On the other hand, the data of Examples 1 and 2 and other symbols ● (all confirmed to be Zr ₂ ON ₂ were confirmed by the diffraction pattern of the thin film X-ray) were all in the range of 5.0 to 5.4 eV. Thus, a high oxygen reduction starting potential exceeding 0.75 V was obtained. As shown in FIG. 11, the formation of Zr ₂ ON ₂ was confirmed in all the thin film X-ray diffraction patterns of the catalyst in which a high oxygen reduction starting potential exceeding 0.75 V was obtained.
In addition to Examples 1 and 2, the sample with the symbol ● where the ionization potential was 5.4 eV or more was maintained in a stream of ammonia (1 dm ³ / min) at 900 ° C. for 30 to 60 hours in a ZrO ₂ powder. An oxynitriding was performed. From the result of powder XRD, it was confirmed that the crystallinity was high as Zr ₂ ON ₂ . These Zr ₂ ON ₂ have an oxygen reduction starting potential of about 0.5 V and an extremely low oxygen reduction activity.
From the above results, it was found that a Zr compound having a highly crystalline Zr ₂ ON ₂ structure is important for the oxygen reduction catalytic ability. From FIG. 12, it was found that the ionization potential of the electrode catalyst of the present invention is preferably 5.4 eV or less, more preferably 5.1 to 5.4 eV.

Zr ₂ ON ₂ has been studied as a photocatalyst and has a band gap of 2.6 eV (T. Mishima, M. Matsuda, and M. Miyake, Appl. Catal. A Gen, 324, 77 (2007).) It is known that the upper energy level of the valence band should be lower than −5.6 eV which is the standard electrode potential of the oxygen electrode reaction. Therefore, pure substance Zr ₂ ON ₂ is not expected to have high oxygen reduction catalytic ability.
Fig. 13 shows the expected electronic states of ZrO ₂ and pure substance Zr ₂ ON ₂ based on literature (JW Schultze and AW Hassel, "Encyclopedia of Electrochemistry Vol. 4", WILEY-VCH Verlag GmbH & Co.) KGaA (2003), 234. and U. Vohrer, H.-D. Wiemhofer, W. Gopel, BA Van Hassel, and AJ Burggraaf, Solid State Ionics, 59, 141 (1993)). FIG. 13 shows that the band gap decreases with nitridation of ZrO ₂ and, at the same time, the upper energy level of the valence band approaches -5.6 eV. Therefore, the ionization potential of Zr ₂ ON ₂ as a pure substance is considered to be 5.6 eV or more.
As shown in FIG. 13, since the ionization potential of ZrO ₂ is 7.4 eV, the ionization potential decreases with a change from ZrO ₂ to Zr ₂ ON ₂ . In general, it is known that the ionization potential of an oxide increases with the adsorption of oxygen to the metal surface, and conversely decreases with an increase in defect density on the oxide surface. Therefore, the ionization potential of the Zr thin film with the Zr ₂ ON ₂ structure is smaller than expected from ZrO ₂ or Zr ₂ ON ₂ , indicating the possibility of oxygen or nitrogen defects on the surface. It is thought that.

It is a figure which shows the cross-sectional TEM image of an electrode thin film. It is a figure which shows the X-ray-diffraction chart of the thin film of FIG. It is another figure which shows the cross-sectional TEM image of an electrode thin film. It is another figure which shows the cross-sectional TEM image of an electrode thin film. It is a figure which shows the X-ray-diffraction chart of the thin film of FIG. It is a figure which shows the electric current-potential curve of the electrode using the electrode material of Example 1. FIG. It is a figure which shows the Tafel plot of an electric current-potential curve. It is another figure which shows the Tafel plot of an electric current-potential curve. It is a figure which shows the relationship between the sputtering conditions at the time of preparation of an electrode thin film, and oxygen reduction start potential. It is another figure which shows the relationship between the sputtering conditions at the time of preparation of an electrode thin film, and oxygen reduction start potential. It is a figure which shows the X-ray-diffraction chart of the thin film of Example 2 and Comparative Examples 4 and 5. FIG. It is a figure which shows the relationship between ionization energy and oxygen reduction start potential. The literature is a diagram showing the ionization energy of the Zr ₂ ON ₂ and ZrO ₂ pure substance.

Claims (3)

The crystal structure by X-ray diffraction is ZrO _1/2 N, and the potential at which the oxygen reduction current starts flowing when the potential scan is performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. is a reversible hydrogen. Electrocatalyst characterized by being 0.75 V or more based on electrode potential. The electrode catalyst according to claim 1, wherein the ionization potential is 5.4 eV or less. An electrode comprising the electrode catalyst fine particles according to claim 1 or 2 supported thereon.