Microfabrication of the Ammonia Plasma-Activated Nickel Nitride-Nickel Thin Film for Overall Water Splitting in the Microfluidic Membraneless Electrolyzer

Hydrogen production in the microfluidic alkaline membraneless electrolyzer (mu AME) marks a new paradigm in sustainable energy technology. One challenge in this field is implementing a bifunctional catalyst to catalyze hydrogen evolution reaction and oxygen evolution reaction using methods compatible with microfabrication techniques. Herein, the scalable synthesis, micropatterning, and performance of a nickel nitride (Ni3N/Ni) bifunctional catalyst are demonstrated. Microfabrication is used to pattern Ni microelectrodes, and nitridation and N-H grafting of the electrodes-which also act as the catalysts-are achieved by ammonia plasma. These electrodes are incorporated into the mu AME device, and the electrolyte flow rate is optimized to maximize gas product separation. The mu AME is operated in a two-electrode configuration exhibiting a current density of 263.73 mA cm(-2) at 2.5 V and a stable 6 h operation for overall water splitting. The mu AME performance efficiency is 99.86%, with a current density of 150 mA cm(-2). Gas chromatography of the electrolysis products revealed no gas cross-over across the electrodes. Volumetric collection efficiencies of 97.72% for H-2 and 96.14% for O-2 are obtained. The performance of the mu AME is comparable to a membrane-based electrolyzer operating under stringent conditions of high temperature (60-80 degrees C) and extreme electrolyte pH (30-40 wt % KOH).