Electronic structure modification of ultrathin MnFeOOH and integration with Ni3S2 as bifunctional electrocatalysts for improved alkaline water splitting

Developing high-performance transition metal electrocatalysts is crucial for large-scale electrolysis of water to produce hydrogen. Ni3S2 is a promising bifunctional water splitting electrocatalyst but has the problem of weak adsorption of water molecules and hydroxide ions. In order to develop it into a high-performance bifunctional electrocatalyst, in this work it was hybridized with MnFeOOH to optimize the chemical adsorption of oxygen- and hydrogen-containing intermediates. By altering the ratio of Mn and Fe, the electronic structure of the catalyst is adjusted. Through the implementation of these strategies, the water electrolysis performance of the composite catalyst has been effectively improved. It was revealed that when the Mn/Fe ratio was 2 : 1, its electrocatalytic oxygen evolution performance was optimal, and only an overpotential of 268.4 or 339.4 mV was needed to realize a current density of 100 or 200 mA cm−2; when the Mn/Fe ratio was 1 : 3, the HER performance was the best, which only required 94.6 and 257.6 mV to afford current densities of 10 and 50 mA cm−2, respectively; chronoamperometric i–t tests show that these electrocatalysts have excellent durability. A two-electrode overall water splitting device constructed with them can realize a current density of 10 mA cm−2 at only 1.6 V. This work provides insights for the development of high-performance bifunctional electrocatalysts.