Bio-inspired nickel-iron-based organogel: an efficient and stable bifunctional electrocatalyst for overall water splitting at high current density.

Developing a platinum group metal (PGM) free electrocatalyst remains a prime challenge for cost effective green hydrogen (H) production. Herein, mimicking the PS II catalyst, a bimetallic organogel of nickel (Ni), iron (Fe) and benzotriazole (NiFe-gel) is developed as an efficient electrocatalyst. The developed synthetic strategy is simple and scalable, and most importantly, no binder is required for gel-loaded electrode preparation. The respective gel-based electrode showed excellent bifunctionality, in both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), water electrolysis activity in low and high current density (: 110 mV and : 260 mV for the OER and : 88 mV and : 324 mV for the HER), low Tafel slope and outstanding stability for 100 h at a current density of 1 A cm. The two-electrode electrolyser using the developed NiFe-gel in the anode and cathode setups for overall water splitting attained current densities of 10 mA cm and 1 A cm at potentials of 1.49 V and 1.89 V, respectively. Most significantly, NiFe-gel loaded anion exchange membrane based 4 cm alkaline water electrolysis (AEMAWE) attained a current density of 1.08 A cm at 50 °C and 2 V and showed stability for at least 100 h. Very nominal performance reduction was observed upon scale-up of the electrolyser from 4 cm to 9 cm, and the performance was better than the targeted AEMAWE performance of ≥1 A cm at 2 V. This excellent performance is attributed to the synergistic electronic interaction between Fe and Ni, interaction of nitrogen rich triazole moieties attached to the metal site, similar to the PS II system, and porous electrode microstructure. Thus, the NiFe-gel might be a potential PGM-free electrocatalyst for industrial scale hydrogen production through water electrolysis.