Bornoz, P.; Abdi, F.F.; Tilley, S.D.; Dam, B.; van de Krol, R.; Graetzel, M.; Sivula, K.: A Bismuth Vanadate-Cuprous Oxide Tandem Cell for Overall Solar Water Splitting. The Journal of Physical Chemistry C 118 (2014), p. 16959-16966

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.