Amorphous silicon carbide photoelectrode for hydrogen production directly from water using sunlight

Abstract

Results on the use of amorphous silicon carbide (a-SiC:H) as a photoelectrode in an integrated ‘hybrid’ photoelectrochemical (PEC) cell to produce hydrogen directly from water using sunlight are presented. A high quality a-SiC:H thin film with bandgap >2.0eV was fabricated by RF-PECVD technique using a SiH₄, H₂ and CH₄ gas mixture. Incorporation of the carbon in the a-SiH film not only increased the bandgap, but also led to an increase in corrosion resistance in an electrolyte. Adding H₂ during the fabrication process led to a decrease in the density of states (DOS) in the films. Immersing the a-SiC:H(p)/a-SiC:H(i) structure in a pH 2 electrolyte showed excellent durability up to 100 h (so far tested); the photocurrent increased and the photocurrent onset shifted anodically after the 100-h durability test, which is encouraging. It was also found that a SiO _x layer is formed on the surface of a-SiC:H when exposed to air, which led to a decrease in the photocurrent, and the photocurrent onset shifted cathodically. We have found that this effect could be removed via a hydrofluoric acid dip and the photocurrent could be increased to over 6mA/cm² at a potential of −1.4V (versus Ag/AgCl). To boost the photovoltage (potential) required for water splitting, the configuration of a-Si:H tandem (or ‘micromorph’)/a-SiC:H structure (PV/PEC) could be viable for water splitting. As a first step, we integrated amorphous silicon tandem solar cells with an a-SiC:H photoelectrode, which exhibited encouraging results. Finally, via simulation, we showed that using a-SiC:H as a photoelectrode could lead to a solar-to-hydrogen (STH) conversion efficiency >10%.