FAC-Induced Regulation of Nickel Active Sites to Trigger Kinetic Promotion of Electrochemical-/Solar-Driven Water Splitting

The exploration of inexpensive electrocatalysts for overall water splitting to harvest hydrogen fuel has become a research hotspot in view of sustainability and pure hydrogen energy. Herein, we report Ni and Ni3C-supported graphitized carbon nitride (FAC) prepared via a single-step incineration method using biowaste fish scales as the carbon source, where KOH is employed as an activator to obtain Ni@Ni3C/FAC-K with a caterpillar bundle structure and high porosity with more N- and O-containing groups. The synergistic coupling among Ni, Ni3C, and FAC could increase the number of catalytic sites, wettability, and surface area and reduce the energy barrier for fast electron and mass transfer of active species to boost the catalytic activity. The optimal Ni@Ni3C/FAC-K exhibits high intrinsic oxygen evolution reaction (OER) activity (GC/NF: η10-291/261 mV; 65/65 mV dec–1; 24/100 h) compared to Ni@Ni3C/FAC-C and benchmark IrO2/RuO2. Operando electrochemical impedance spectroscopy (EIS) reveals the low resistance and high conductivity of Ni@Ni3C/FAC-K. Bode analysis is performed at various potentials to confirm the exceptional activities. The temperature effect analysis infers that Ni@Ni3C/FAC-K shows a low activation energy (Ea) of 3.57 kJ/mol compared to that of Ni@Ni3C/FAC-C (10.12 kJ/mol). The Trumpet plot reveals the formation of O2 bubbles from Ni@Ni3C/FAC-K compared to Ni@Ni3C/FAC-C. Besides, an alkaline electrolyzer and a solar cell-driven alkaline electrolyzer built with a Ni@Ni3C/FAC-K anode achieve an exceptional overall water-splitting efficiency (1.60 V @10 mA/cm2) with high performance maintained over 100 h, establishing its potential for industrial applications. The alternate process with the Ni@Ni3C/FAC-K anode to generate green H2 is eco-beneficial for converting solid waste into renewable resources. This simple method for preparing Ni@Ni3C/FAC-K may provide a promising path for converting low-value biowaste fish scales into high-value energy conversion catalysts.