Gold Doping in a Layered Co‐Ni Hydroxide System via Galvanic Replacement for Overall Electrochemical Water Splitting

The development of active yet stable bifunctional materials to produce hydrogen and oxygen via electrochemical water splitting is an ongoing challenge. Here, a system based on electrodeposited Ni(OH) 2 and Co(OH) 2 containing highly distributed gold nanoparticles at less than 0.25 at% to facilitate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions is developed. The key aspect is using galvanic replacement to deposit gold on a layer of electrodeposited Co(OH) 2 prior to electrodepositing Ni(OH) 2 . The fabrication of a composite system based on Co(OH) 2 ‐Au‐Ni(OH) 2 is required for optimal activity for both the HER and OER. The composite is characterized with helium ion microscopy, transmission electron microscopy, depth profiling X‐ray photoelectron microscopy, and a variety of electrochemical techniques. This material exceeds the activity of Pt for the HER at current densities greater than 40 mA cm −2 and is stable for both reactions for prolonged periods of electrolysis. In a two‐electrode configuration, current densities greater than 175 mA cm −2 for overall water splitting could be readily achieved at an applied voltage of 1.90 V in a commercially relevant electrolyte of 6 m NaOH.