Efficient and Stable Silicon Photocathodes Coated with Vertically Standing Nano-MoS₂ Films for Solar Hydrogen Production

Abstract

Water splitting in a photoelectrochemical cell, which converts sunlight into hydrogen energy, has recently received intense research. Silicon is suitable as a viable light-harvesting material for constructing such cell; however, there is a need to improve its stability and explore a cheap and efficient cocatalyst. Here we fabricate highly efficient and stable photocathodes by integrating crystalline MoS catalyst with ∼2 nm AlO protected np-Si. AlO acts as a protective and passivative layer of the Si surface, while the sputtering method using a MoS target along with a postannealing leads to a vertically standing, conformal, and crystalline nano-MoS layer on AlO/np-Si photocathode. Efficient (0.4 V vs RHE onset potential and 35.6 mA/cm saturated photocurrent measured under 100 mA/cm Xe lamp illumination) and stable (above 120 h continuous water splitting) photocathode was obtained, which opens the door for the MoS catalyst to be applied in photoelectrochemical hydrogen evolution in a facile and scalable way.

Directly Assembled 3D Molybdenum Disulfide on Silicon Wafer for Efficient Photoelectrochemical Water Reduction

“…[35,36] More importantly, in the 3D MoS 2 /TiO 2 /p-Si photocathode, the variation of R in both R versus θ and R versus λ is negligible, indicating that the 3D MoS 2 film has omnidirectional and broadband antireflective properties for p-Si, presumably because of the size effect below the diffraction limit. [41] For the saturation current density and the current density at zero bias voltage, our photocathode shows the highest photocurrent density, mostly because of the improvement of charge generation efficiency and lower interfacial charge resistance. The saturation current density of the 3D MoS 2 /TiO 2 /p-Si is ≈37 mA cm −2 , whereas it was 33 and 32 mA cm −2 for the layered MoS 2 /TiO 2 /p-Si and TiO 2 /p-Si, respectively.…”

“…Because of the highly populated edge-sites, the potential of our photocathodes at www.advsustainsys.com 1 mA cm −2 is comparable with those of the previously reported photocathodes which are MoS x /MoS 2 /Mo/n + p-Si, [38] MoS 2 /Ti/ n + p-Si, [39] [Mo 3 S 13 ] 2− /MoS 2 /Mo/n + p-Si [40] or MoS 2 /Al 2 O 3 /n + p-Si. [41] For the saturation current density and the current density at zero bias voltage, our photocathode shows the highest photocurrent density, mostly because of the improvement of charge generation efficiency and lower interfacial charge resistance. Table 1, where the charge transfer resistance from silicon to TiO 2 was almost equal for both the photocathodes, 3D MoS 2 /TiO 2 /p-Si and TiO 2 /p-Si, which are 45 and 40 Ω cm 2 , respectively.…”

Strategies for Semiconductor/Electrocatalyst Coupling toward Solar‐Driven Water Splitting

“…Besides the conventional metal‐ or metal oxide‐based HER and OER catalysts, metal nonoxides have recently drawn considerable attention for use to catalyze the HER and OER, which have demonstrated catalytic performance comparable to that of PGM counterparts . For example, molybdenum sulfide (MoS 2 ) and selenide (MoSe 2 ) were studied intensively for use as an HER or OER catalyst given their decent catalytic activity and outstanding electrochemical stability in a wide pH range, and therefore many efforts have recently been made to couple semiconductor light absorbers with MoS 2 or MoSe 2 using PVD . Shen's group reported direct deposition of MoS 2 and MoSe 2 , respectively, on n + p‐Si photocathodes using magnetron sputtering .…”

“…For example, molybdenum sulfide (MoS 2 ) and selenide (MoSe 2 ) were studied intensively for use as an HER or OER catalyst given their decent catalytic activity and outstanding electrochemical stability in a wide pH range, and therefore many efforts have recently been made to couple semiconductor light absorbers with MoS 2 or MoSe 2 using PVD . Shen's group reported direct deposition of MoS 2 and MoSe 2 , respectively, on n + p‐Si photocathodes using magnetron sputtering . Upon sputtering, a continuous, vertically standing, grass‐like MoS 2 or MoSe 2 layer with abundant exposed active edge sites was formed on Al 2 O 3 passivated pyramidal n + p‐Si wafers.…”

“…Upon sputtering, a continuous, vertically standing, grass‐like MoS 2 or MoSe 2 layer with abundant exposed active edge sites was formed on Al 2 O 3 passivated pyramidal n + p‐Si wafers. The as‐fabricated MoS 2 /Al 2 O 3 /n + p‐Si photocathode could generate a photocurrent density of −32.4 mA cm −2 at 0 V RHE with an outstanding catalytic stability of 120 h for the HER under illumination, due to the formed favorable band structure, which allowed better charge transfer from Si to MoS 2 . Besides direct deposition, MoS 2 catalyst was also reported to couple with semiconductor photoelectrodes using a two‐step procedure.…”