A tandem photoelectrochemical cell based on Cu2-xTe nanocrystals for solar energy conversion to hydrogen

In this work we present the design, assembly and characterization of a tandem photoelectrochemical (PEC) cell based on two different crystallographic phases of substoichiometric
copper telluride nanocrystals (NCs). The first one, a pseudo-cubic phase, pc-Cu2-xTe, is characterized by positive photocurrents, while the second one,
a hexagonal phase, h-Cu2-xTe, favors negative ones. Taking advantage of the different optoelectronic properties of the two Cu2-xTe structures, we prepared a PEC cell
composed of a hybrid pc-Cu2-xTe/TiO2 photoanode, with TiO2 acting as a light absorber and electron selective layer, and a h-Cu2-xTe/CuI photocathode, with CuI
behaving as a photo-absorber and hole selective layer. The tandem PEC cell shows a photocurrent density of ~0.5 mA/cm2 when measured in a 2-electrode
configuration without any co-catalyst. Finally, to test the PEC cell performance for the hydrogen evolution reaction (HER), a thin film of Pt was deposited on top
of the photocathode and ~7 μmol of hydrogen were obtained at 0.6 V in a 1-h experiment, reaching a photocurrent of 1 mA/cm2 with no losses.