A freestanding nanoporous NiCoFeMoMn high-entropy alloy as an efficient electrocatalyst for rapid water splitting

The development of low-cost non-noble-metal-based electrocatalysts that can work stably at high current densities is crucial to apply a hydrogen evolution reaction (HER) and an oxygen evolution reaction (OER) in electrolyzed water. This study developed a freestanding nanoporous high-entropy alloy foil as a dual-functional electrocatalyst. The proposed electrocatalyst combines dealloying and polarization and shows excellent electrocatalytic activity in an alkaline electrolyte. It has an extremely small overpotential of 150 mV at 1,000 mA cm−2 for the HER and a low Tafel slope of 29 mV dec−1. At the same current density, the overpotential of the OER is only 350 mV. The alkaline electrolyzer using the electrocatalyst as both anode and cathode requires a cell voltage of only 1.47 V to output a stable current density of 10 mA cm−2. This enables it to be an efficient bifunctional electrocatalyst for alkaline overall water splitting and better stability for more than 375 h of continuous hydrogen production while providing substantial material cost savings relative to platinum. Density functional theory calculations indicate that the ultrahigh HER activity of the catalyst originates from the synergetic effect of optimized hydrogen adsorption in the segregation area and enhanced H2O adsorption in the un-segregation area produced by spinodal decomposition.