Increased Oxygen Evolution Activity in pH-Universal Electrocatalyst: Urea-Modified NiFeCoCN Medium-Entropy Alloy

The kinetic process of a slow oxygen evolution reaction (OER) always constrains the efficiency of overall water electrolysis for H-2 production. In particular, nonprecious metal electrodes for the OER have difficulty in possessing excellent electrocatalytic activity and stability in pH-universal media simultaneously. In this work, urea is first used as a pore-forming agent and active C/N source to fabricate a nanoporous NiFeCoCN medium-entropy alloy (MEA) by high-temperature sintering based on the nanoscale Kirkendall effect. The NiFeCoCN MEA achieves an overpotential of 432 mV at a current density of 10 mA.cm(?2) and a lower Tafel slope of 52.4 mV.dec(?1) compared to the IrO2/Ti electrode (58.6 mV.dec(?1)) in a 0.5 mol/L H2SO4 solution. In a 1 mol/L KOH solution, the NiFeCoCN MEA obtains an overpotential of 175 mV for 10 mA.cm(?2) and a Tafel slope of 40.8 mV.dec(?1), which is better than IrO2/Ni foam. This work proves a novel strategy to design and prepare nanoporous MEA materials with desirable C/N species, which provides promising prospects for the industrial production of H-2 energy.

Automated summary

In this study, urea was used as a template and active C/N source to fabricate a nanoporous NiFeCoCN medium-entropy alloy (MEA) by high-temperature sintering based on the nanoscale Kirkendall effect. The NiFeCoCN MEA exhibited excellent electrocatalytic activity and stability in both acidic and alkaline media, outperforming the traditional IrO2/Ti and IrO2/Ni foam electrodes.