Study On The Preparation And Oxygen Evolution Properties Of （Mn,Co）_xCr_1-xO_3/2 Electrocatalysts

The research on hydrogen production from water splitting has attractedconsiderable interest, and the study on the catalysts of cathode and anode issharply increased. More and more people pay close attention to non-noble metaloxide catalyst, due to its good catalytic performance and low price. In ourresearch, transition metal mixed oxides of Mn and Cr with nominalcompositional formula, MnxCr1-xO3/2(x=0,0.2,0.4,0.6,0.8and1.0) andtransition metal mixed oxides of Co and Cr with nominal compositional formula,CoxCr1-xO3/2(x=0,0.2,0.4,0.6,0.8and1.0) were obtained by a thermaldecomposition method, and the products were analyzed by scanning electronmicroscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectronspectroscopy (XPS). And the electrochemical properties of the catalysts foroxygen evolution reaction (OER) in alkaline solution were evaluated by linearsweep voltammetry (LSV), staircase voltammetry and chronoamperometrytesting. The results are as follows:1. The preparation of MnxCr1-xO3/2catalystsManganous acetate and chromium chloride were taken as the sources of Mn and Cr, respectively. The transition metal mixed oxides catalysts,MnxCr1-xO3/2,with different nominal compositional formulas, were prepared bya thermal decomposition method. The surface morphology of the electrodes, thecrystal form of the catalysts and the valance state of element were analyzed bySEM, XRD and XPS. The catalytic activity, overpotential and stability of theelectrode were determined by linear sweep voltammetry (LSV), staircasevoltammetry and chronoamperometry testing. Then we can get the best catalyticperformance of electrode with molar ratio of manganese and chromium. Theresult shown that the mixture was the solid solution of Mn2O3(bixbyite) andCr2O3(eskolaite), and the surface of the electrode was obviously rough withcracks at x=0.2. The electric catalytic performance testing shown that whenx=0.2, the catalyst had best catalytic activity in OER process at high potentialregion (1.0V vs Ag/AgCl), the current density of Mn0.2Cr0.8O3/2electrode wasabout9times higher than that of Cr2O3, and80times higher than Mn2O3, andthe staircase voltammetry testing also shown that its overpotential (η=237.7mVat a current density of1mA cm-2) was much lower than that of single Mn2O3(η=996.5mV) and Cr2O3(η=450.5mV) catalysts. The stability testing showedthat the mixed oxides had good stabilities in strong alkaline solution during OERprocess.2. The preparation of CoxCr1-xO3/2catalystsCobalt chloride and chromium chloride were taken as the sources of Co andCr, respectively. The transition metal mixed oxides catalysts, CoxCr1-xO3/2,with different nominal compositional formulas, were prepared by a thermaldecomposition method. The surface morphology of the electrodes, the crystalform of the catalysts and the valance state of element were analyzed by SEM,XRD and XPS. The catalytic activity, overpotential and stability of the electrodewere determined by linear sweep voltammetry (LSV), staircase voltammetry andchronoamperometry testing. Then we can get the best catalytic performance ofelectrode with molar ratio of manganese and chromium. The result shown thatthe mixture was the solid solution of Co3O4and eskolaite-Cr2O3, and the surfaceof the electrode was much roughness with cracks at x=0.2. The electro-catalyticperformance testing shown that when x=0.2, the catalyst had best catalyticactivity in OER process at high potential region (1.0V vs Ag/AgCl), the currentdensity of Co0.2Cr0.8O3/2electrode was about3.75times higher than that of Cr2O3,and15.2times higher than Co3O4, and the staircase voltammetry testing alsoshown that its overpotential (η=70.3mV at a current density of1mA cm-2) wasmuch lower than that of single Co3O4(η=610.9mV) and Cr2O3(η=435.0mV)catalysts. The stability testing showed that the mixed oxides had good stabilitiesin strong alkaline solution during OER process.