Corrosion‐Resistant and High‐Entropic Non‐Noble‐Metal Electrodes for Oxygen Evolution in Acidic Media

Abstract

carrier, in addition to the application of fuel cells operating on hydrogen-rich fuel. Water electrolysis driven by renewable energy is a promising technology [1][2][3] for hydrogen production with zero emission. Water electrolysis can be classified into the following types: alkaline, [4] proton exchange membrane (PEM), [5,6] and anion exchange membrane (AEM). [7,8] Compared to the other types, PEM-type water electrolysis is considered to be more ecofriendly and efficient because it generates no waste, produces highly pure H 2 gas (>99.9999 vol%), [9] and displays a high discharge H 2 pressure (3.0-7.6 MPa) [10] and a high current density (1.0-4.0 A cm −2 ) at low overpotentials (1.5-1.9 V). [3,6,10,11] In contrast, alkaline-and AEM-type water electrolysis produces H 2 with >99.5 vol% and >99.99 vol% purities, respectively. However, efficient electrocatalytic reactions in these systems require considerable amounts of noble metals, for example, 300 kg of Pt in the cathode and 700 kg of Ir in the anode per 1.0 GW of power input of the PEM-type electrolyzer. [11] The serious scarcity of noble metals, especially that of Ir (global production: ≈7 ton year −1 ), [11] To realize a sustainable hydrogen economy, corrosion-resistant non-noblemetal catalysts are needed to replace noble-metal-based catalysts. The combination of passivation elements and catalytically active elements is crucial for simultaneously achieving high corrosion resistance and high catalytic activity. Herein, the self-selection/reconstruction characteristics of multielement (nonary) alloys that can automatically redistribute suitable elements and rearrange surface structures under the target reaction conditions during the oxygen evolution reaction are investigated. The following synergetic effect (i.e., cocktail effect), among the elements Ti, Zr, Nb, and Mo, significantly contributes to passivation, whereas Cr, Co, Ni, Mn, and Fe enhance the catalytic activity. According to the practical water electrolysis experiments, the self-selected/reconstructed multi-element alloy demonstrates high performance under a similar condition with proton exchange membrane (PEM)-type water electrolysis without obvious degradation during stability tests. This verifies the resistance of the alloy to corrosion when used as an electrode under a practical PEM electrolysis condition.

The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni–Cr–Mo Alloys

“…Commonly used electrochemical techniques for studying passivity and corrosion of stainless steel may not be directly applicable to Ni-based alloys because the measured electrochemical current is not only due to corrosion reactions. [32] NiO and MoO 2 are good catalysts for the oxygen evolution reaction (OER), [33][34][35][36][37][38][39] which adds another dimension of complexity to understanding the degradation of Ni-Cr-Mo alloys since OER is known to be coupled with dissolution and degradation in other related materials. [40][41][42][43][44][45] The oxidation and corrosion of Ni alloys have previously been studied with electrochemical measurements, [20,31] X-ray photoelectron spectroscopy (XPS), [23,[27][28][29][46][47][48] scanning tunneling microscopy, [21,30,49] time-of-flight secondary-ion mass spectrometry, [50,51] transmission electron microscopy and energy loss spectroscopy, [52,53] operando neutron reflectivity, [54,55] and inline inductively coupled plasma mass spectrometry.…”

Nonprecious High‐Entropy Chalcogenide Glasses‐Based Electrocatalysts for Efficient and Stable Acidic Oxygen Evolution Reaction in Proton Exchange Membrane Water Electrolysis

“…This is believed to be because Mo and W metals play roles as passivation elements by forming metal hydroxides or oxides, hence contributing to the suppression of corrosion of the CoFeNiMoWTe. [ 43–46 ] These results suggest that the excellent acidic OER stability of the CoFeNiMoWTe is attributed to the combined effects of high configuration entropy and high corrosion‐resistance ability by Mo and W elements in the CoFeNiMoWTe N‐ HECGs catalyst to consistently achieve the high catalytic activity.…”

“…This is believed to be because Mo and W metals play roles as passivation elements by forming metal hydroxides or oxides, hence contributing to the suppression of corrosion of the CoFeNiMoWTe. [43][44][45][46] These results suggest that the excellent acidic OER stability of the CoFeNiMoWTe is attributed to the combined effects of high configuration entropy and high corrosion-resistance ability by Mo and W elements in the CoFeN-iMoWTe N-HECGs catalyst to consistently achieve the high catalytic activity. To further address the effect of constituent elements and their high entropy nature on the electrochemical catalytic behavior and stability of the CoFeNiMoWTe N-HECGs, we prepared multielements controlled electrocatalysts with various composition combinations of different constituent elements using the same synthetic approach, and summarized their catalytic activities in Figure 3d, Figures S8 and S9, and Table S2, Supporting Information.…”

Electrocatalysts for the Oxygen Evolution Reaction in Acidic Media

“…Notably, a recently reported high‐entropic alloy (HEA) with nine elements (Ti, Cr, Mn, Fe, Co, Ni, Zr, Nb, and Mo), which underwent elements redistribution and structure rearrangement during the OER, showed high acidic OER activity and stability. [ 287 ] The high corrosion resistance and catalytic activity were attributed to the passivation and active elements in the HEA, respectively. Although the HEA was proposed as a promising acidic OER catalyst, the dissolution of active sites was not carefully analyzed.…”