Photoelectrochemical properties of the crednerite CuMnO2 and its application to hydrogen production and Mn+ reduction (Mn+ Cd2+, Pd2+, Zn2+, Ni2+, and Ag+)

The crednerite CuMnO2 was synthesized by sol-gel method under N-2 flow. The oxide crystallizes in a monoclinic symmetry ascribed to the Jahn-Teller Mn3+ ion and the formation is completed above 600 degrees C. The XPS analysis confirms the mono and trivalent states of copper and manganese. CuMnO2 exhibits a direct optical gap of 1.70 eV and the p-type conductivity is due to oxygen insertion in the Cu layers. An exchange current density (0.2 mA cm(-2)) and a corrosion potential (similar to - 0.816 V-SCE) indicate a stable compound in neutral solution (pH similar to 7). The flat band potential (E-fb = 0.17 V-SCE) and the holes density (NA- = 7.25 x 10(15) cm(-3)) were determined from the capacitance measurement (C-2 - E). The conduction band made up of Cu-3d orbital is located at (3.43 +/- 0.02) eV below vacuum and the electrons can reduce heavy metals to their elemental states. Indeed, CuMnO2 was successfully used for the photodeposition of Cd2+, Pd2+, Zn2+, Ni2+, and Ag+ (30 mg L-1) under visible-light illumination. The best reduction was obtained with Zn2+ (94%) because of the optimal band bending, due to the redox potential of Zn2+ and its adsorption. By contrast, Ag+ (76%) was weakly deposited owing to its positive potential. The metal photodeposition proceeds competitively with the water reduction and decelerates over time. The species showing the high H-2 evolution exhibits the lower Mn+ reduction and the medium pH makes the M-n(+) deposition easier. The best photocatalytic H2 evolution (1.02 mL g(-1) min(-1)) occurred with Cd2+.

Automated summary

CuMnO2 synthesized by sol-gel method exhibits stable p-type conductivity and efficient photocatalytic performance under visible light illumination in neutral solution.