Trimetal-based N-doped carbon nanotubes arrays on Ni foams as self-supported electrodes for hydrogen/oxygen evolution reactions and water splitting

Rational design of non-noble metal-based bifunctional electrocatalysts for hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) is still a challenge in water splitting. Herein, a MOF-on-MOF (MOF = metal-organic framework) strategy is developed to obtain trimetal-based nitrogen-doped carbon nanotubes arrays loaded on nickel foams (denoted as FeNiCo@NC/NF). Benefiting from the superior compositional and structural feature, FeNiCo@NC/NF self-supported electrodes exhibit excellent bifunctional HER and OER activity with a low overpotential of 145 and 245 mV at 10 mA cm(-2). When simultaneously used as cathode and anode for water splitting, it only requires 1.61 V to achieve 10 mA cm(-2) and even outperforms the benchmark electrode couple of Pt/C parallel to RuO2 at higher current densities. Studies discover that trimetallic FeNiCo nanoparticles can provide more synergetic metal active sites, interconnected N-doped carbon nanotubes arrays can offer more effective electron transports channels, and conductive Ni foam substrate can reduce the internal impedance of the material. Density functional theory (DFT) calculations also demonstrate that FeNiCo@NC/NF electrode possesses a favorable Gibbs free energy of hydrogen adsorption (Delta GH*) value of -0.13 eV, which is benefit for its superior HER activity. Overall, our work reports an efficient self-supported electrode for hydrogen/oxygen evolution reactions and water splitting.