Steps Towards a Sustainable Hydrogen Production from Sunlight and Water

This chapter focuses on some aspects concerning the realization of an actually sustainable H2 production, and especially the need for earth abundant, environmental friendly, solar driven heterogeneous catalysis for the Water Oxidation reaction: the catalyst shall be thermodynamically and mechanically stable to allow cyclic long-term operations. The focus will be mainly on Mn- and Co-compounds, though reference will be made to other compounds, when appropriate

A bismuth vanadate–cuprous oxide tandem cell for overall solar water splitting

Through examination of the optoelectronic and photoelectrochemical properties of BiVO4 and Cu2O photoelectrodes, we evaluate the feasibility of a BiVO4/Cu2O photoanode/photocathode tandem cell for overall unassisted solar water splitting. Using state-of-the-art photoelectrodes we identify current-matching conditions by altering the photoanode active layer thickness. By further employing water oxidation and reduction catalysts (Co-Pi and RuOx, respectively) together with an operating point analysis, we show that an unassisted solar photocurrent density on the order of 1 mA cm–2 is possible in a tandem cell and moreover gain insight into routes for improvement. Finally, we demonstrate the unassisted 2-electrode operation of the tandem cell. Photocurrents corresponding to ca. 0.5% solar-to-hydrogen conversion efficiency were found to decay over the course of minutes because of the detachment of the Co-Pi catalyst. This aspect provides a fundamental challenge to the stable operation of the tandem cell with the currently employed catalysts