Stable Unassisted Solar Water Splitting on Semiconductor Photocathodes Protected by Multifunctional GaN Nanostructures

Abstract

Producing hydrogen by unassisted solar water splitting is one essential step to make direct solar fuel conversion a viable energy source. To date, however, there has been no demonstration of stable photoelectrodes for high-efficiency photoelectrochemical water splitting. In this work, we report that a GaInP 2 /GaAs/Ge triple-junction (3J) photocathode protected by multifunctional GaN nanostructures can enable both efficient and relatively stable solar water splitting. A 12.6% solar-to-hydrogen (STH) efficiency is measured without any external bias. Of particular importance, we demonstrate relatively stable solar water splitting for 80 h in three-electrode configuration and 57 h in twoelectrode measurement at zero bias. This is the best reported stability for multijunction III-V semiconductor photocathodes in two-electrode configuration to our knowledge. The multifunctional GaN nanostructure significantly reduces the charge transfer resistance at the semiconductor/electrolyte interface and protects III−V materials against corrosion. Such multifunctional GaN photocatalytic nanostructures provide a new pathway to improve the performance of conventional photoelectrodes to achieve both efficient and stable unassisted solar water splitting.

Recent Progress in Gallium Nitride for Photoelectrochemical Water Splitting

“…The methods to enhance efficiency are mainly carried out in the following four aspects, such as morphology, doping, surface modification, and composition of solid solution or multiple-metal incorporation. Up to now, GaN has made great progress in the application of PEC water splitting; the solar-to-hydrogen efficiency of 12.6% has already been obtained without any external bias [98], better than CoP catalyst electrodes (6.7%) reported recently [99], but it still not as excellent as TiO 2 (18.5%) [100]. And its properties need to be further optimized to improve the absorption efficiency of visible light, increase the carrier migration speed, and facilitate carrier transport.…”

Modulating Surface/Interface Structure of Emerging InGaN Nanowires for Efficient Photoelectrochemical Water Splitting

“…In order to address the current matching related issues for dual‐absorber device, tunnel junction has been widely employed for III‐V absorbers system. [ 29,133 ] Fan et al. successfully fabricated a monolithically integrated p‐InGaN/n‐GaN/Si adaptive tunnel junction photocathode without the strict current matching requirement.…”

“…In order to address the current matching related issues for dual-absorber device, tunnel junction has been widely employed for III-V absorbers system. [29,133] Fan et al successfully fabricated a monolithically integrated p-InGaN/n-GaN/Si adaptive tunnel junction photocathode without the strict current matching requirement. [134] The n-GaN and p-InGaN NWs were connected by an n ++ -GaN/InGaN/p ++ -GaN tunnel junction, and these structures were grown on a Si solar cell wafer.…”

“…[25,26] In addition, the long-term stability of photoelectrode in harsh conditions and cost issues are critical for the practical application of PEC water splitting. [27][28][29]…”

Enhancement of Interfacial Charge Transportation Through Construction of 2D–2D p–n Heterojunctions in Hierarchical 3D CNFs/MoS2/ZnIn2S4 Composites to Enable High‐Efficiency Photocatalytic Hydrogen Evolution

“…To date, extensive striving have been committed to broaden visible‐light responsive photocatalysts for high‐efficiency H 2 production. [ 1–4 ] Among the various catalysts, such as transition metal nitrides, [ 5–7 ] the 2D ternary chalcogenide ZnIn 2 S 4 is a highly promising n‐type semiconductor for photocatalytic H 2 evolution, [ 8–10 ] thanks to its good visible‐light‐harvesting capability (energy bandgap [ E g ] = 2.34–2.48 eV), photostability, and nontoxicity. [ 11,12 ] Yet the single‐phase ZnIn 2 S 4 catalyst typically suffers from serious deterioration in both photocatalytic activity over H 2 evolution, due to its physical and structural deficiencies.…”