Recent progress in photocathodes for hydrogen evolution

Abstract

Solar water splitting, which has been a topic of intensive research interest for several decades, is one of the promising approaches to utilize renewable energy to maintain the sustainable prosperity of our society. However, up to now no mature photoelectrochemical cell can be used in practical large-scale applications because of the difficulties to satisfy all the harsh requirements, including high energy conversion efficiency, high stability and low cost. This feature article reviews the recent progress in developing photocathodes in photoelectrochemical cell for solar hydrogen production. Both the developments of the p-type semiconductor light absorbers and the efforts to develop synergistic approaches to improve the overall performance of the photocathode are discussed.

Nanostructured p-Type Semiconductor Electrodes and Photoelectrochemistry of Their Reduction Processes

“…This plot evidences the differences between p-type cuprous oxide, cadmium sulfide and copper gallium selenide, and shows the decrease of the overall efficiency of photoelectrochemical conversion upon increase of photocathode bandgap. This calculated trend is independent on the positions of the band edges of the three p-type photocathodes ( Figure 16) [119]. A selection of the most relevant results recently achieved with water splitting photocathodes are presented in Tables 2 and 3 [121][122][123].…”

“…Metal sulfide photocathodes like CoS [96], CoS2 [97,98] [99]), nitrides of semi-and non-metallic atoms (GaN [112] and C3N4 [113]), borides of metals (Co2B [114]), arsenides of semi-metallic atoms or non-metals (GaPNAs [115], GaAs [116], AlGaAs [116]), tellurides of metals (CdTe QD [73]), and carbides of semi-metallic atoms (4H-SiC [117], 3C-SiC [118]). From the thermodynamic standpoint photoactivated HER can take place provided that p-type photoelectrodes have a small bandgap with respect to the energy separation of water splitting levels, and the lower edge of CB is above the energy level of H + reduction (Figures 16 and 17) [98,119]. Cu 2 O in the morphology of nanowires [83] was also decorated with RuO x catalyst for H 2 generation [62].…”

“…IP is the ionization potential energy evaluated with respect to the vacuum level. Adapted from reference [119].…”

Enhancing photoelectrochemical activity with three-dimensional p-CuO/n-ZnO junction photocathodes

“…However, there are just few reports on p-type semiconductor based photocathodes, among which copper oxide has been extensively investigated due to the abundance in Earth's crust, high photoactivity, low cost, and nontoxicity [17][18][19][20]. Particularly, it has a lower conduction band position than the reduction potential of water.…”

Towards efficient solar-to-hydrogen conversion: Fundamentals and recent progress in copper-based chalcogenide photocathodes

“…However, comparatively, very little work has been carried out on p-type semiconductors as photocathodes for water reduction [22,23]. The photocathodes based on ptype semiconductors can be cathodically protected from the photooxidation to some extent, because photoexcited holes would be transferred to an outer circuit before the photocorrosion due to the band bending at the photoelectrode/electrolyte interface and an applied external potential.…”