Accelerating Hydrogen Desorption of Nickel Molybdenum Cathode via Copper Modulation for Pure-Water-Fed Hydroxide Exchange Membrane Electrolyzer

The more sluggish kinetics of hydrogen evolution catalysts in base as compare to that in acid to some degree restricts hydrogen production performance of hydroxide exchange membrane electrolyzers, especially when using earth-abundant catalysts. Here a ternary nickel-copper-molybdenum hydrogen evolution catalyst is reported that exhibits approximate to 5 times higher turnover frequency than without copper doping. The X-ray absorption near-edge structure and valence band spectrum demonstrate that the light doping of copper into nickel-molybdenum alloy modulates the electronic structure and downshifts the d-band center, resulting in accelerated hydrogen desorption, as consolidated by H2 temperature programmed desorption and theoretical calculation. An electrolyzer employing this cathode catalyst and a nickel-iron anode, gives a current density of 1.7 A cm-2 at 2.0 V with a pure-water feed through the anode, which outperforms the 2025 target proposed by the United States Department of Energy, and even is operated continuously for over 1000 h with a decay rate of as low as 0.5 mV h-1. Post-mortem analysis discloses that hydroxide exchange ionomer migration is one of the key factors affecting long-term durability. This work demonstrates the feasibility of a low-cost, water-fed hydroxide exchange membrane electrolyzer achieving industrial-level performance and lifetime. An efficient and stable nickel-copper-molybdenum hydrogen evolution catalyst is developed by modulating the d-band center. When coupled with nickel-iron anode, it achieves an impressive performance and durability in a pure-water-fed hydroxide exchange membrane electrolyzer employing all earth-abundant catalysts.image