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 TiO 2 -encapsulated carbon-nitride (CN x ) (denoted as TiO 2 [email protected] x ) is developed, which is derived from the Ti 3 C 2 T x and melamine–cyanuric acid calcinated at different temperatures. Among the series of TiO 2 [email protected] x nanosheets, the TiO 2 [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 TiO 2 nanoparticles. When TiO 2 [email protected] x,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 TiO 2 [email protected] x,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.