Surface-Tailored InP Nanowires via Self-Assembled Au Nanodots for Efficient and Stable Photoelectrochemical Hydrogen Evolution

With a band gap close to the Shockley–Quiesser limit and excellent conduction band alignment with the water reduction potential, InP is an ideal photocathode material for photoelectrochemical (PEC) water reduction. Here, we develop facile self-assembled Au nanodots based on dewetting phenomena as a masking technique to fabricate wafer-scale InP nanowires (NWs) via a top-down approach. In addition, we report dual-function wet treatment using sulfur-dissolved oleylamine (S-OA) to remove a plasma-damaged surface in a controlled manner and stabilize InP NWs against surface corrosion in harsh electrolyte solutions. The resulting InP NW photocathodes exhibit an excellent photocurrent density of 33 mA/cm2 under 1 sun illumination in 1 M HCl with a highly stabilized performance without needing additional protection layers. Our approach combining large-area NW fabrication and surface engineering synergistically enhances light harvesting and PEC performance and stability, thereby providing a pathway for the development of efficient and durable InP photoelectrodes in a scalable manner

InGaAsP as a Promising Narrow Band Gap Semiconductor for Photoelectrochemical Water Splitting

While photoelectrochemical (PEC) water splitting is a very promising route toward zero-carbon energy, conversion efficiency remains limited. Semiconductors with narrower band gaps can absorb a much greater portion of the solar spectrum, thereby increasing efficiency. However, narrow band gap (∼1 eV) III–V semiconductor photoelectrodes have not yet been thoroughly investigated. In this study, the narrow band gap quaternary III–V alloy InGaAsP is demonstrated for the first time to have great potential for PEC water splitting, with the long-term goal of developing high-efficiency tandem PEC devices. TiO2-coated InGaAsP photocathodes generate a photocurrent density of over 30 mA/cm2 with an onset potential of 0.45 V versus reversible hydrogen electrode, yielding an applied bias efficiency of over 7%. This is an excellent performance, given that nearly all power losses can be attributed to reflection losses. X-ray photoelectron spectroscopy and photoluminescence spectroscopy show that InGaAsP and TiO2 form a type-II band alignment, greatly enhancing carrier separation and reducing recombination losses. Beyond water splitting, the tunable band gap of InGaAsP could be of further interest in other areas of photocatalysis, including CO2 reduction

Manipulating Intermediates at the Au–TiO₂ Interface over InP Nanopillar Array for Photoelectrochemical CO₂ Reduction

Photoelectrochemical (PEC) reduction of CO2 with H2O is a promising approach to convert solar energy and greenhouse gas into value-added chemicals or fuels. However, the exact role of structures and interfaces of photoelectrodes in governing the photoelectrocatalytic processes in terms of both activity and selectivity remains elusive. Herein, by systematically investigating the InP photocathodes with Au–TiO2 interfaces, we discover that nanostructuring of InP can not only enhance the photoresponse owing to increased light absorption and prolonged minority carrier lifetime, but also improve selectivity toward CO production by providing more abundant interfacial contact points between Au and TiO2 than planar photocathodes. In addition, theoretical studies on the Au–TiO2 interface demonstrate that the charge transfer between Au and TiO2, which is locally confined to the interface, strengthens the binding of the CO* intermediate on positively charged Au interfacial sites, thus improving CO2 photoelectroreduction to form CO. An optimal Au–TiO2/InP nanopillar-array photocathode exhibits an onset potential of +0.3 V vs reversible hydrogen electrode (RHE) and a Faradaic efficiency of 84.2% for CO production at −0.11 V vs RHE under simulated AM 1.5G illumination at 1 sun. The present findings of the synergistic effects of the structure and interface on the photoresponse and selectivity of a photoelectrode provide insights into the development of III–V semiconductor-based PEC systems for solar fuel generation