Stable and efficient multi-crystalline n+p silicon photocathode for H2 production with pyramid-like surface nanostructure and thin Al2O3 protective layer

Abstract

When a Si photocathode is used in a photoelectrochemical cell for H2 production, an open nanostructure capable of enhanced light absorption, low surface recombination, and being fully protected by thin protective layer is highly desirable. Here, we explored a highly stable and efficient multi-crystalline (mc) n+p silicon photocathode. A pyramid-like surface nanostructure on mc-Si wafer was fulfilled through a two-step metal-catalyzed chemical etching process, and then a n+p junction photocathode protected by a thin Al2O3 layer was constructed. The photocathode exhibits a high stability of continuous photoelectrochemical H2 production for above 100 h after a thin layer of Al2O3 is coated on its surface, and its energy conversion efficiency can be up to 6.8% after Pt loading, due to the lowered surface light reflection, increased surface area and minority carrier life time on the electrode surface.

Chalcopyrite Thin Film Materials for Photoelectrochemical Hydrogen Evolution from Water under Sunlight

“…In the case of the photoanode, self-oxidation makes it difficult to utilize non-oxide materials. In contrast, the photocathode can be made of a non-oxide material, such as p-type Si [16][17][18][19], copper oxide [20,21], phosphides [22][23][24][25], and oxysulfides [26,27]. Most photocathodes showing a relatively high half-cell solar-to-hydrogen conversion efficiency (HC-STH) [28] have been composed of single-crystalline materials, as in the cases of Si, InP, and InGaP2, owing to their low defect densities; however, these electrodes require time-consuming and costly processes to fabricate.…”

Stable Hydrogen Production from Water on an NIR‐Responsive Photocathode under Harsh Conditions

“…Figure a,b demonstrates that there was no clear change in the sample morphology, confirming that a dense RuO 2 layer remained intact during the HER for at least 17 h. By contrast, a gradual collapse of the surface modifiers occurred in the case of a Pt/Mo/Ti‐modified sample, resulting in the appearances of many cracks within 9 h, as can be seen from Figure d. The majority of protective layer materials, such as TiO 2 , require heat treatment during and/or after deposition on a photoelectrode surface . This heat treatment is required to stabilize the layers, but can have negative effects, as discussed in the Introduction.…”

“…Coating the electrode surface with protective substances such as metal oxides is considered to be one means of mitigating the degradation of nonoxide photocathodes . However, it is important for the protective layer to conform to and fully cover the surface, without forming pinholes .…”

Improved photoelectrochemical hydrogen evolution using a defect-passivated Al2O3 thin film on p-Si

“…In attempts to overcome this kinetic limitation, recent developments in Si photocathodes for the HER have led to significantly enhanced performance in PEC cells. For instance, utilizing nanostructured Si photocathodes [5][6][7][8], coating the HER catalyst [8][9][10], and doping to create an n + p-Si buried junction [3,11] have led to PEC performance enhancement. Moreover, loading a passivation layer on the surface of Si is also a good solution because of two reasons.…”