A hierarchically porous and hydrophilic 3D nickel–iron/MXene electrode for accelerating oxygen and hydrogen evolution at high current densities

Electrocatalytic water-splitting is one of the most economical and clean way for high-purity hydrogen production utilizing renewable energy sources. Key issue to large-scale implementation of this technology is the lack of efficient electrocatalysts that can deliver large current density at low overpotential for oxygen and hydrogen evolution reactions (OER and HER). Herein, we report a strategy leveraging 3D MXene frame with high conductivity, highly hydrophilic properties and kinetics-favorable architecture as multi-functional structural scaffold for engineering water-splitting electrocatalysts yielding high current densities. The macroporous 3D MXene frame not only facilitates the mass/charge transport across the catalyst, but also accelerates the OER redox process of NiFe-LDHs and the Volmer step of HER by enhancing the water adsorption/activation on the catalyst. Commercially required high current density of 500 mA cm−2 can be achieved at low overpotentials for both OER (300 mV) and HER (205 mV) with good durability in 1.0 M KOH. Alkaline electrolyzer using this electrocatalytic electrode as both the anode and cathode exhibit low cell voltage for achieving high current density of 500 mA cm−2 with high Faradaic efficiency and excellent durability. Their performance outperforms the Pt/C–RuO2 couple and the state-of-the-art electrocatalysts for overall water-splitting in alkaline electrolyte.