The development of efficient and stable non-noble metal bifunctional electrocatalysts for overall water splitting in acidic and alkaline media is highly desirable for industrial water electrolysis, but remains a profound...

Developing highly efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) in alkaline and neutral media is crucial but still a significant challenge due to the sluggish multi-step reaction kinetics...

In this work, a multi-interfacial nickel phosphide-nitride/nickel (NiPN/Ni) nanoparticle (NP)-decorated P,N-doped carbon nanotube (CNT) forest on carbon cloth (NiPN/Ni/CC-CNT2) with a high electrochemical active surface area was synthesized by a facile two-step approach involving the CNT forest growth with a subsequent controlled phosphorization/nitridation procedure, in which the initially loaded Ni species (active sites for growing CNT forest) serve as a precursor for synthesizing NiPN/Ni NP active species on CNT forest for water electrolysis. This is the first example that the loaded Ni sites for CNT forest growth were directly converted to active species for water electrolysis rather than be removed by acid treatment, which fully utilizes Ni resources and simultaneously avoids the waste acid environmental pollution. Thanks to the promoted mass/electron transfer by the CNT forest structure and the improved intrinsic activity by the multi-interfacial synergistic effect of nickel phosphide-nitride and nickel, the resultant NiPN/Ni/CC-CNT2 shows high activity toward hydrogen evolution reaction (HER, η10 = 56 mV and η100 = 186 mV) and oxygen evolution reaction (OER, η10 = 204 mV and η100 = 266 mV) in an alkaline medium. In addition, the assembled two-electrode electrolyzer with NiPN/Ni/CC-CNT2 as both the anode and cathode delivers low cell voltages of 1.49 and 1.74 V for 10 and 100 mA cm–2, respectively, associated with an excellent electrocatalytic durability for overall water splitting. The developed low-cost bifunctional NiPN/Ni/CC-CNT2 outperforms most of the reported electrocatalysts in literature and performs even better than the Pt and RuO2 benchmark electrocatalysts for HER and OER, respectively, at a large current density. Therefore, the fabricated NiPN/Ni/CC-CNT2 has shown great potential for large-scale commercial production of green hydrogen as a clean and renewable fuel to support the carbon neutralization strategy.