Fundamental Insights into High-Temperature Water Electrolysis Using Ni-Based Electrocatalysts

Hydrogen production from water electrolysis using solid oxide electrolysis cells (SOECs) has attracted considerable attention because of favorable kinetics and thermodynamics associated with operation at elevated temperatures. In the present work, we employ density functional theory calculations combined with microkinetic modeling to investigate the factors that govern this process on Ni and Ni-based alloy electrocatalysts. Our studies show that H 2 O dissociation is the rate-limiting step on Ni(111) and Ni(211), with Ni(211) exhibiting the lowest barrier for this step. The effect of alloying Ni with another metal on the energetics associated with this process is also investigated. Our studies show that the binding energies of the most abundant intermediates, OH and O, become gradually weaker, and the barriers for water dissociation become gradually higher as Ni is alloyed with metals from left to right in the periodic table. A volcano-type relationship between the calculated electrochemical rates and the binding energies of O is found, with the Ni/Fe alloy exhibiting the highest rate among the Ni alloys considered. These predictions are consistent with the reported experimental results, suggesting that these structure/performance relationships can be used to guide the design of heterogeneous electrocatalysts for high-temperature water electrolysis.