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. TiO 2 -coated InGaAsP photocathodes generate a photocurrent density of over 30 mA/cm 2 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 TiO 2 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 CO 2 reduction.
A combined theoretical and experimental approach demonstrates that nanocluster embedment into the pores of metal-organic frameworks (MOF) may be influenced by the chemical functionalisation of the MOF. Furthermore, this results in the surface functionalisation of the embedded nanoclusters, highlighting the potential of MOF scaffolds for the design and synthesis of novel functional materials.
and photovoltaic-electrochemical (PV-EC) [11][12][13] water splitting have reignited interest in the prospect of a sustainable hydrogen economy, with several efficiency records being broken in quick succession. Immersed photoelectrodes and PEC systems have long been a tantalizing goal, simultaneously offering the advantages of both PC and PV-EC systems while avoiding many of their respective drawbacks. First, photoelectrodes are compact, lowering material usage and electrical losses. This also minimizes the distance that photogenerated charge carriers must travel to reach the electrolyte, reducing the ohmic losses associated with carrier collection and subsequent redistribution across the catalytic surface. Second, H 2 and O 2 are evolved at opposite electrodes and can therefore be collected separately. Third, photoelectrodes do not require additional thermal management, as the electrolyte itself can act as a coolant. [14] This becomes particularly useful when operating under concentrated light. Despite recent breakthroughs, the stabilization of highefficiency photoelectrodes remains a key issue; no previously reported immersed system has maintained a solar-to-hydrogen (STH) efficiency of over 10% for longer than 5 days. [9] Instability is often encountered due to the fact that many proven An ideal catalytic interface for photoelectrodes that enables high efficiency and long-term stability remains one of the keys to unlocking high-performance solar water splitting. Here, fully decoupled catalytic interfaces realized using surfacestructured cocatalyst foils are demonstrated, allowing optimized photoabsorbers to be combined with high-performance earth-abundant cocatalysts. Since many earth-abundant cocatalysts are deposited via solution-based methods, deposition on chemical-sensitive photoabsorbers is a significant challenge. By synthesizing cocatalyst foils prior to device fabrication, photoabsorbers are completely isolated from corrosive chemical environments and are provided with outstanding protection during operation. Si and GaAs photoelectrodes prepared using Ni-based cocatalyst foils achieve excellent half-cell efficiencies and generate stable photocurrents for over 5 days. Furthermore, a GaAs artificial leaf achieves a solar-to-hydrogen efficiency of 13.6% and maintains an efficiency of over 10% for longer than nine days, an accomplishment that has not been previously reported for an immersed solar water splitting system. These results, together with theoretical calculations of other photoelectrode systems, demonstrate that cocatalyst foils offer a very attractive method for fabricating high-performance solar water splitting systems.
The research interest in photoelectrochemical (PEC) water splitting is ever growing due to its potential to contribute towards clean and portable energy. However, the lack of low energy band gap materials with high photocorrosion resistance is the primary setback inhibiting this technology from commercialisation. The ternary alloy InGaN shows promise to meet the photoelectrode material requirements due to its high chemical stability and band gap tunability. The band gap of InGaN can be modulated from the UV to IR regions by adjusting the In concentration so as to absorb the maximum portion of the solar spectrum. This paper reports on the influence of In concentration on the PEC properties of planar and nanopillar (NP) InGaN/GaN multi-quantum well (MQW) photoanodes, where NPs were fabricated using a top-down approach. Results show that changing the In concentration, while having a minor effect on the PEC performance of planar MQWs, has an enormous impact on the PEC performance of NP MQWs, with large variations in the photocurrent density observed. Planar photoanodes containing MQWs generate marginally lower photocurrents compared to photoanodes without MQWs when illuminated with sunlight. NP MQWs with 30% In generated the highest photocurrent density of 1.6 mA cm, 4 times greater than that of its planar counterpart and 1.8 times greater than that of the NP photoanode with no MQWs. The InGaN/GaN MQWs also slightly influenced the onset potential of both the planar and NP photoanodes. Micro-photoluminescence, diffuse reflectance spectroscopy and IPCE measurements are used to explain these results.
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.
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