Acid-durable, high-performance cobalt phosphide catalysts for hydrogen evolution in proton exchange membrane water electrolysis

Abstract

The cost of platinum group metal (PGM) catalysts is one of the major obstacles in commercializing proton exchange membrane water electrolyzers (PEMWEs). The non-PGM substituents are often more financially beneficial but low in activity and durability in the acidic environment. In this study, cobalt phosphide catalysts, which are promising non-PGM alternatives for the hydrogen evolution reaction (HER) and have enhanced durability and single-cell performance, were fabricated directly on carbon paper using the pulse electrodeposition method. As the dissolution potential (reported as -x vs saturated calomel electrode) of the pulse electrodeposition shifted in the positive direction, the P/Co ratio of the Co-P-x catalysts increased because of severe Co dissolution. Among the catalysts, Co-P-0.6, Co-P-0.5, and Co-P-0.4 (where the number indicates the negative dissolution potential) were rapidly degraded in acid, whereas Co-P-0.3, Co-P-0.2, and Co-P-0.1 showed high stability because of the relative amounts of CoP and Co2P phases. The acid-dissolved Co-P-0.3 catalyst showed the best half-cell performance (an overpotential of 143.85 mV at 10 mA/cm(2)) and durability, and the P-Co and Co delta+ surface states are critical for its performance. Single-cell tests using the Co-P-0.3 cathode revealed its remarkable performance of 1.89 A/cm(2) at 2.0 V-cell, indicating its promise as a non-PGM cathode material for PEMWEs.