Hollow bimetallic selenide derived from a hierarchical MOF-based Prussian blue analogue for urea electrolysis

Because of its low thermodynamic voltage (0.37 V), the urea oxidation reaction (UOR) is an ideal method to replace the OER, accelerate the anodic oxidation reaction and reduce the energy consumption of overall water splitting. In this work, bimetallic selenide with a hollow nanocube structure exhibits remarkable catalyst activity towards the UOR. A hierarchical MOF-based Prussian blue analogue (PBA) is constructed by growing Ni–Co PBA on an MOF–Ni template. By controlling the reaction time and temperature, the Ni–Co Prussian blue analogue (denoted as PBA@MOF–Ni) has the morphology of nanocubes evenly growing on flower-like MOF–Ni. After the selenide reaction by a solvothermal method, PBA@MOF–Ni is converted to Co–Ni/Se (denoted as PBA@MOF–Ni/Se), which has a structure with hollow nanocubes and maintains the shape of a flower. This hierarchical MOF-based PBA selenide exhibits good catalytic activity due to the addition of MOFs and the synergistic effect of bimetals. PBA@MOF–Ni/Se can be used as both a cathode and an anode in urea electrolysis. In particular for the UOR, the performance of PBA@MOF–Ni/Se is much better than that for the OER. In the performance comparison between urea electrolysis and water splitting, PBA@MOF–Ni/Se∥PBA@MOF–Ni/Se only needs 1.49 V to reach 10 mA cm−2, which is much lower than the voltage required for water splitting.