Expanding Multinary Selenide Based High-Efficiency Oxygen Evolution Electrocatalysts through Combinatorial Electrodeposition: Case Study with Fe-Cu-Co Selenides

Developing low-cost electrocatalysts with high efficiency for water splitting is a critical task to make this technology viable for large-scale clean energy generation. Transition metal selenides, comprising earth abundant elements, such as Fe, Co and Cu, have gained attention as superior electrocatalysts for oxygen evolution reaction (OER) in the alkaline medium. In this article, we have systematically investigated the evolution of OER catalytic activity as a function of composition for a series of Fe-Co-Cu quaternary selenides by exploring a trigonal phase diagram. The OER activity was dependent on the quantity of Cu and Fe in the Fe-Cu-Co-Se quaternary selenide electrocatalysts, while surprisingly, Fe-Cu ternary selenides exhibit reduced OER activity in comparison to their pure parent compounds FeSe and Cu3Se2. Quaternary selenides exhibited more efficient catalytic activity with increasing amount of Fe or Cu in the catalysts, and the quaternary mixed metal selenide thin film of composition (Fe0.48Co0.38Cu0.14)Se showed the best catalytic performance with a small overpotential of 256 mV at 10 mA cm(-2) and a low Tafel slope of 40.8 mV dec(-1) in N-2 -saturated 1.0 M KOH solution. The outstanding catalytic performance of quaternary selenides may be explained by the possible electron cloud delocalization among the transition metal sites in the catalytic system through d-bands, leading to lower charge transport resistance at the catalyst-electrolyte interface as well better film conductivity, as has also been observed through electrochemical impedance spectroscopy. Such enhanced charge transfers eventually facilitate the rate of O-2 release from the catalyst surface, leading to enhanced activity.