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 TiO2C@CNx) is developed, which is derived from the Ti3C2Tx and melamine-cyanuric acid calcinated at different temperatures. Among the series of TiO2C@CNx nanosheets, the TiO2C@CNx,950 (obtained by calcination at 950 degrees 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 TiO2C@CNx,950 is used as the electrocatalyst for water splitting, a current density of 10 mA cm(-2) (E-j = 10) is achieved at a low cell voltage of 1.50 V vs. reversible hydrogen electrode. Meanwhile, the overall oxygen activity of the TiO2C@CNx,950 exhibits good reversible oxygen reaction, giving a small potential difference between the E-j = 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 H-2 at the cathode and O-2 at the anode. Consequently, this work can pave a path for developing multifunctional electrocatalysts for water spitting and liquid Zn-air battery.