Attuning the Electronic Properties of Two-Dimensional Co-Fe-O for Accelerating Water Electrolysis and Photolysis

Two-dimensional (2D) materials such as layered double hydroxides (LDH) are promising electrocatalysts, especially for water oxidation, owing to their unique physical and electronic properties besides having adequate surface area and availability of unsaturated active metal centers. Herein, we illustrate the high-temperature transformation of bimetallic LDH to semicrystalline 2D metal oxide nanoplates that can maneuver their electronic properties and thereby accelerate the water dissociation reactions. The nanoplates prepared at 300 °C require only 280 ± 13 and 177 ± 7 mV overpotentials for oxygen/hydrogen evolution reactions (OER and HER) to achieve a current density of ±10 mA cm^-2 in 1 M KOH, respectively. In a two-electrode water splitting cell, while this bifunctional catalyst needs 1.69 V to deliver a current density of 10 mA cm^-2, the LDH precursor demands a cell voltage of 1.93 V. However, both the catalysts demonstrate excellent durability for more than 200 h. When the bifunctional metal oxide electrolyzer is connected to perovskite solar cells for unassisted solar-driven water splitting, impressively, such an integrated photovoltaic-electrolyzer can achieve a solar-to-hydrogen (STH) efficiency of 9.3%. The predominantly superior catalytic activity of the nanoplates is due to the abundance of unsaturated oxygen which decreases the free energy of adsorption of the intermediates.