Abstract
The combination of earth-abundant catalysts and semiconductors, for example, molybdenum sulfides and planar silicon, presents a promising avenue for the large-scale conversion of solar energy to hydrogen. The inferior interface between molybdenum sulfides and planar silicon, however, severely suppresses charge carrier extraction, thus limiting the performance. Here, we demonstrate that defect-free gallium nitride nanowire is ideally used as a linker of planar silicon and molybdenum sulfides to produce a high-quality shell-core heterostructure. Theoretical calculations revealed that the unique electronic interaction and the excellent geometric-matching structure between gallium nitride and molybdenum sulfides enabled an ideal electron-migration channel for high charge carrier extraction efficiency, leading to outstanding performance. A benchmarking current density of 40 ± 1 mA cm−2 at 0 V vs. reversible hydrogen electrode, the highest value ever reported for a planar silicon electrode without noble metals, and a large onset potential of +0.4 V were achieved under standard one-sun illumination.
Highlights
The combination of earth-abundant catalysts and semiconductors, for example, molybdenum sulfides and planar silicon, presents a promising avenue for the large-scale conversion of solar energy to hydrogen
Molybdenum sulfides (MoSx), which have received tremendous attention in recent years[16,17], are considered as a promising catalyst to accelerate the kinetics of planar silicon because of its superior hydrogen evolution reaction (HER) catalytic activity and low cost[18,19,20]
The utilization of conventional MoSx/planar Si as photocathodes for achieving high performance still remains a grand challenge, due to the inefficient solar light harvesting of planar Si related to the strong scattering of light[23], and limited surface area of planar Si leading to a low density of exposed active sites[24]
Summary
The combination of earth-abundant catalysts and semiconductors, for example, molybdenum sulfides and planar silicon, presents a promising avenue for the large-scale conversion of solar energy to hydrogen. The utilization of conventional MoSx/planar Si as photocathodes for achieving high performance still remains a grand challenge, due to the inefficient solar light harvesting of planar Si related to the strong scattering of light[23], and limited surface area of planar Si leading to a low density of exposed active sites[24] Most importantly, it is of difficulty in realizing efficient charge carrier extraction between MoSx and planar Si for high solar-to-hydrogen efficiency because of the interfacial defects, chemical incompatibility, and synthesis difficulties[25]. The recent development of molecular beam epitaxy leads to controlled synthesis of single-crystal GaN nanowire arrays on planar Si with a high-quality interface and dramatically reduced manufacturing cost[27] These as-grown GaN nanowire arrays possess defect-free structure and large charge carrier mobility, resulting in efficient charge carrier extraction from Si substrate[28]. The structure of nanowire arrays is beneficial for exposing high-density active sites and enhancing solar light absorption[29,30]
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