Electronic and Surface Modifications of Ni–Co–Fe Oxides: A Catalyst with Maximum Exposure of Fe Active Sites for Water Electrolysis

Abstract

The production of green hydrogen through water electrolysis is a crucial component of sustainable energy systems. One key challenge is the development of cost-effective electrocatalysts with high performance.Here, we report on the fabrication of a multilayered electrode by coating a nickel foam with nickel−cobalt−iron (Ni−Co−Fe) oxide layers (NiCoFe@ NF/SD). The detailed physical and electrochemical characterizations demonstrated that the topmost layer is rich in Fe active sites. The electronic shuffling between the different layers creates an optimal environment for intermediate adsorption−desorption during the oxygen and hydrogen evolution reactions. The NiCoFe@NF/SD electrode exhibits high catalytic performance due to the presence of intrinsically reactive active sites, as well as high structural, chemical, and mechanical durability with a low overpotential of 210 and 166 mV for the oxygen and hydrogen evolution reactions, respectively, to deliver a geometric activity of 20 mA cm −2 . In a two-electrode configuration, NiCoFe@NF/SD as cathode and anode requires a relatively small input voltage of 1.56 V to deliver a current density of 10 mA cm −2 and sustained a current density of 100 mA cm −2 for over 90 h with no noticeable degradation. This work offers a simple approach for the rational design of electrodes to produce green hydrogen through water electrolysis.

Single Entity Electrocatalysis

“…In the above reactions, * denotes the position of the active site on the electrode surface and H* denotes the H atom adsorbed on the active site. HER is typically kinetically sluggish and requires large overpotentials to achieve relevant activity. , As with most electrocatalytic reactions, the ultimate reaction rate and resulting activity of HER electrocatalysts depends heavily on the composition, , morphology, − and electronic configuration , of the catalyst , (because this involves an adsorption process) as well as the electrolysis conditions (i.e., electrolyte identity and concentration, − pH, ,− , and temperature − ). When compared to more complicated reactions (such as CO 2 RR which can involve several electron transfer steps, intermediates, and potential products), HER is a relatively straightforward two-electron reaction that does not suffer from challenges in product selectivity.…”