Integrated Bifunctional Electrodes Based on Amorphous Co-Ni-S Nanoflake Arrays with Atomic Dispersity of Active Sites for Overall Water Splitting.

Fabrication of amorphous electrocatalysts without noble metals for cost-effective full water splitting is highly desired but remains a substantial challenge. In the present work, we report a facile strategy for exploring integrated bifunctional electrocatalysts based on amorphous cobalt/nickel sulfide nanoflake arrays self-supported on carbon cloth, by tailoring competitive coordination of metal ions between glucose and 2-aminoterephthalic acid. Ultrahigh dispersion of binary metal active sites with balanced atomic distribution enables the optimization of catalytic properties for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in an alkaline solution. The obtained catalyst exhibits remarkably enhanced OER and HER activities as compared with its oxide counterpart and analogues with different Co/Ni ratios. It requires overpotentials of 296 and 192 mV to deliver a current density of 10 mA cm for the OER and HER, respectively; it retains 96.6 and 96.9% activity after 32 h of OER and 36 h of HER tests at 10 mA cm, respectively. As directly used an anode and a cathode in an alkaline electrolyzer, a low cell voltage of 1.60 V could endow a water splitting current of 10 mA cm, outperforming the benchmark RuO and Pt/C-based electrolyzer at 1.72 V@10 mA cm. The current synthetic strategy may provide more opportunities for the design and direct synthesis of amorphous catalysts for overall water splitting and beyond.