Hydrothermal electrochemical flow reactor to independently control temperature, pressure, and potential for manganese oxide electrodeposition

Electrodeposition has been widely applied for the fabrication of functional materials; however, most previous deposition processes were limited to temperatures of less than 100 degree celsius. Furthermore, reaction pressure was concomitantly determined with the reaction temperature, hindering the full exploration of synthetic conditions. Here, we developed a hydrothermal electrochemical flow reactor equipped with flowing system and that enables the independent control of temperature and pressure and applied this reactor to the synthesis of manganese oxides (MnOx) for electrochemical oxygen evolution reaction. Systematic investigation of temperature and pressure revealed that the crystallinity and morphology of MnOx was influenced by deposition temperature, with particle size decreasing under higher pressure (4 MPa). Electrodeposition at higher temperature (160 degree celsius) at 1 MPa generated a mixed phase of epsilon- and gamma- MnO2, which showed superior electrochemical water oxidation activity to samples prepared at lower temperature (80 and 100 degree celsius, respectively), achieving a current density of 10 mA cm(-2) for at least 100 h under acidic conditions (pH 2.3). Our results show that the hydrothermal electrochemical flow reactor allows expanding synthetic parameters for the synthesis of highly functional catalytic materials.