The rational design of earth-abundant catalysts with excellent water splitting activities is important to obtain clean fuels for sustainable energy devices. In this study, mixed transition metal oxide nanoparticles encapsulated in nitrogendoped carbon (denoted as AB₂O₄@NC) were developed using a one-pot protocol, wherein a metal–organic complex was adopted as the precursor. As a proof of concept, MnCo₂O₄@NC was used as an electrocatalyst for water oxidation, and demonstrated an outstanding electrocatalytic activity with low overpotential to achieve a current density of 10 mA·cm^-1 (η₁₀ = 287 mV), small Tafel slope (55 mV·dec^-1), and high stability (96% retention after 20 h). The excellent electrochemical performance benefited from the synergistic effects of the MnCo₂O₄ nanoparticles and nitrogen-doped carbon, as well as the assembled mesoporous nanowire structure. Finally, a highly stable all-solid-state supercapacitor based on MnCo₂O₄@NC was demonstrated (1.5% decay after 10, 000 cycles).

The development of efficient, low-cost, stable, non-noble-metal electrocatalysts for water splitting, particularly those that can catalyze both the hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode, is a challenge. We have developed a facile method for synthesizing CoSe₂ nanoparticles uniformly anchored on carbon fiber paper (CoSe₂/CF) via pyrolysis and selenization of in situ grown zeolitic imidazolate framework-67 (ZIF-67). CoSe₂/CF shows high and stable catalytic activity in both the HER and OER in alkaline solution. At a low cell potential, i.e., 1.63 V, a water electrolyzer equipped with two CoSe₂/CF electrodes gave a water-splitting current of 10 mA·cm^-2. At a current of 20 mA·cm^-2, it can operate without degradation for 30 h. This study not only offers a cost-effective solution for water splitting but also provides a new strategy for developing various catalytic nanostructures by changing the metal–organic framework precursors.