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

Abstract

Hydrogen production in the microfluidic alkaline membraneless electrolyzer (μAME) 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 μAME device, and the electrolyte flow rate is optimized to maximize gas product separation. The μAME 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 μAME 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 H2 and 96.14% for O2 are obtained. The performance of the μAME is comparable to a membrane-based electrolyzer operating under stringent conditions of high temperature (60–80 °C) and extreme electrolyte pH (30–40 wt % KOH).