Titanium dioxide encapsulated carbon-nitride nanosheets derived from MXene and melamine-cyanuric acid composite as a multifunctional electrocatalyst for hydrogen and oxygen evolution reaction and oxygen reduction reaction

An advanced trifunctional electrocatalyst based on a series of composites composed of TiO2-encapsulated carbon-nitride (CNx) (denoted as TiO2[email protected]x) is developed, which is derived from the Ti3C2Tx and melamine–cyanuric acid calcinated at different temperatures. Among the series of TiO2[email protected]x nanosheets, the TiO2[email protected]x,950 (obtained by calcination at 950 °C) hybrid exhibits robust trifunctional electrocatalytic activity toward the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) by combining the excellent electrochemical activity of the graphene-like nanostructure and the high electrocatalytic performances of TiO2 nanoparticles. When TiO2[email protected]x,950 is used as the electrocatalyst for water splitting, a current density of 10 mA cm−2 (Ej = 10) is achieved at a low cell voltage of 1.50 V vs. reversible hydrogen electrode. Meanwhile, the overall oxygen activity of the TiO2[email protected]x,950 exhibits good reversible oxygen reaction, giving a small potential difference between the Ej = 10 for OER and the half-wave potential for ORR (0.75 V). Moreover, a simply equipped Zn-air battery is assembled using a homemade cathode, showing open-circuit potential of 1.344 V, which also can supplied an electrical power and produced H2 at the cathode and O2 at the anode. Consequently, this work can pave a path for developing multifunctional electrocatalysts for water spitting and liquid Zn–air battery.