Aldehyde reduced Co3O4 to form oxygen vacancy and enhance the electrochemical performance for oxygen evolution reaction and supercapacitors.

Oxygen vacancy is a feasible approach to boost the electrochemical properties for metal oxides. In this work, a Co3O4 with abundant oxygen vacancy is synthesized via aldehyde reduction. After the procedure, the reduced Co3O4 exhibits larger electrochemical active surface areas and better electrical conductivity. These outstanding characteristics can improve its performance of catalytic and energy storage. As for catalyst of oxygen evolution reaction, the reduced Co3O4 delivers a smaller potential of 1.55 V versus the reversible hydrogen electrode to realize a current density of 10 mA cm-2 and a lower Tafel slope of 71 mV dec-1 in alkaline solution, and these values are smaller than those of pristine Co3O4. Especially the reduced Co3O4 possesses superior stability: the measurements of the polarization curves before and after 15h of stability tests basically coincide. In a supercapacitor, the positive electrode of reduced Co3O4 achieves about 1.7 times areal capacitance of pristine Co3O4 at current density of 1 mA cm-2. Significantly, the superior cycling stability is still retained. Also, an aqueous asymmetric supercapacitor is assembled to evaluate the energy storage performance of the R-Co3O4. Moreover, the oxygen vacancy formation strategy for Co3O4 may be generally extended to other metal oxides for application in energy storage and conversion.