Earth-Abundant Tin Sulfide-Based Photocathodes for Solar Hydrogen Production.
ABSTRACT: Tin-based chalcogenide semiconductors, though attractive materials for photovoltaics, have to date exhibited poor performance and stability for photoelectrochemical applications. Here, a novel strategy is reported to improve performance and stability of tin monosulfide (SnS) nanoplatelet thin films for H2 production in acidic media without any use of sacrificial reagent. P-type SnS nanoplatelet films are coated with the n-CdS buffer layer and the TiO2 passivation layer to form type II heterojunction photocathodes. These photocathodes with subsequent deposition of Pt nanoparticles generate a photovoltage of 300 mV and a photocurrent density of 2.4 mA cm-2 at 0 V versus reversible hydrogen electrode (RHE) for water splitting under simulated visible-light illumination (? > 500 nm, Pin = 80 mW cm-2). The incident photon-to-current efficiency at 0 V versus RHE for H2 production reach a maximum of 12.7% at 575 nm with internal quantum efficiency of 13.8%. The faradaic efficiency for hydrogen evolution remains close to unity after 6000 s of illumination, confirming the robustness of the heterojunction for solar H2 production.
Project description:Dye-sensitized photoelectrochemical (DSPEC) cells are an emerging approach to producing solar fuels. The recent development of delafossite CuCrO2 as a p-type semiconductor has enabled H2 generation through the coassembly of catalyst and dye components. Here, we present a CuCrO2 electrode based on a high-surface-area inverse opal (IO) architecture with benchmark performance in DSPEC H2 generation. Coimmobilization of a phosphonated diketopyrrolopyrrole (DPP-P) or perylene monoimide (PMI-P) dye with a phosphonated molecular Ni catalyst (NiP) demonstrates the ability of IO-CuCrO2 to photogenerate H2. A positive photocurrent onset potential of approximately +0.8 V vs RHE was achieved with these photocathodes. The DPP-P-based photoelectrodes delivered photocurrents of -18 ?A cm-2 and generated 160 ± 24 nmol of H2 cm-2, whereas the PMI-P-based photocathodes displayed higher photocurrents of -25 ?A cm-2 and produced 215 ± 10 nmol of H2 cm-2 at 0.0 V vs RHE over the course of 2 h under visible light illumination (100 mW cm-2, AM 1.5G, ? > 420 nm, 25 °C). The high performance of the PMI-constructed system is attributed to the well-suited molecular structure and photophysical properties for p-type sensitization. These precious-metal-free photocathodes highlight the benefits of using bespoke IO-CuCrO2 electrodes as well as the important role of the molecular dye structure in DSPEC fuel synthesis.
Project description:The present study reports the fabrication of CdSe quantum dot (QD)-sensitized photocathodes on NiO-coated indium tin oxide (ITO) electrodes and their H2-generating ability upon light irradiation. A well-established spin-coating method was used to deposit CdSe QD stock solution onto the surface of NiO/ITO electrodes, thereby leading to the construction of various CdSe QD-sensitized photocathodes. The present report includes the construction of rainbow photocathodes by spin-coating different-sized QDs in a sequentially layered manner, thereby creating an energetically favorable gradient for charge separation. The resulting rainbow photocathodes with forward energetic gradient for charge separation and subsequent electron transfer to a solution-based hydrogen-evolving catalyst (HEC) exhibit good light-harvesting ability and enhanced photoresponses compared with the reverse rainbow photocathodes under white LED light illumination. Under minimally optimized conditions, a photocurrent density of as high as 115 ?A?cm-2 and a Faradaic efficiency of 99.5% are achieved, which is among the most effective QD-based photocathode water-splitting systems.
Project description:Nowadays, the efficient, stable, and scalable conversion of solar energy into chemical fuels represents a great scientific, economic, and ethical challenge. Amongst the available candidate technologies, photoelectrochemical water-splitting potentially has the most promising technoeconomic trade-off between cost and efficiency. However, research on semiconductors and photoelectrode architectures suitable for H2 evolution has focused mainly on the use of fabrication techniques and inorganic materials that are not easily scalable. Here, we report for the first time an all solution-processed approach for the fabrication of hybrid organic/inorganic photocathodes based on organic semiconductor bulk heterojunctions that exhibit promising photoelectrochemical performance. The sequential deposition of inorganic material, charge-selective contacts, visible-light sensitive organic polymers, and earth-abundant, nonprecious catalyst by spin coating leads to state-of-the-art photoelectrochemical parameters, comprising a high onset potential [+0.602 V vs reversible hydrogen electrode (RHE)] and a positive maximum power point (+0.222 V vs RHE), a photocurrent density as high as 5.25 mA/cm2 at 0 V versus RHE, an incident photon-to-current conversion efficiency at 0 V versus RHE of above 35%, and 100% faradaic efficiency for hydrogen production. The demonstrated all solution-processed hybrid photoelectrodes represent an eligible candidate for the scalable and low-cost solar-to-H2 conversion technology that embodies the feasibility requirements for large area, plant-scale applications.
Project description:A self-powered ultraviolet (UV) photodetector (PD) based on p-NiO and n-ZnO was fabricated using low-temperature sputtering technique on indium doped tin oxide (ITO) coated plastic polyethylene terephthalate (PET) substrates. The p-n heterojunction showed very fast temporal photoresponse with excellent quantum efficiency of over 63% under UV illumination at an applied reverse bias of 1.2 V. The engineered ultrathin Ti/Au top metal contacts and UV transparent PET/ITO substrates allowed the PDs to be illuminated through either front or back side. Morphology, structural, chemical and optical properties of sputtered NiO and ZnO films were also investigated.
Project description:Tin sulfide (SnS) is known for its effective gas-detecting ability at low temperatures. However, the development of a portable and flexible SnS sensor is hindered by its high resistance, low response, and long recovery time. Like other chalcogenides, the electronic and gas-sensing properties of SnS strongly depend on its surface defects. Therefore, understanding the effects of its surface defects on its electronic and gas-sensing properties is a key factor in developing low-temperature SnS gas sensors. Herein, using thin SnS films annealed at different temperatures, we demonstrate that SnS exhibits n-type semiconducting behavior upon the appearance of S vacancies. Furthermore, the presence of S vacancies imparts the n-type SnS sensor with better sensing performance under UV illumination at room temperature (25 °C) than that of a p-type SnS sensor. These results are thoroughly investigated using various experimental analysis techniques and theoretical calculations using density functional theory. In addition, n-type SnS deposited on a polyimide substrate can be used to fabricate high-stability flexible sensors, which can be further developed for real applications.
Project description:Organic semiconductors have great potential for producing hydrogen in a durable and economically viable manner because they rely on readily available materials and can be solution-processed over large areas. With the objective of building efficient hybrid organic-inorganic photoelectrochemical cells, we combined a noble-metal-free and solution-processable catalyst for proton reduction, MoS3, and a poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ). Different interfacial layers were investigated to improve the charge transfer between P3HT:PCBM and MoS3. Metallic Al/Ti interfacial layers led to an increase of the photocurrent by up to 8 mA cm(-2) at reversible hydrogen electrode (RHE) potential with a 0.6 V anodic shift of the H2 evolution reaction onset potential, a value close to the open-circuit potential of the P3HT:PCBM solar cell. A 50-nm-thick C60 layer also works as an interfacial layer, with a current density reaching 1 mA cm(-2) at the RHE potential. Moreover, two recently highlighted1 figures-of-merit, measuring the ratio of power saved, ?saved,ideal and ?saved,NPAC, were evaluated and discussed to compare the performances of various photocathodes assessed in a three-electrode configuration. ?saved,ideal and ?saved,NPAC use the RHE and a nonphotoactive electrode with an identical catalyst as the dark electrode, respectively. They provide different information especially for differentiation of the roles of the photogenerating layer and catalyst. The best results were obtained with the Al/Ti metallic interlayer, with ?saved,ideal and ?saved,NPAC reaching 0.64% and 2.05%, respectively.
Project description:Two-dimensional (2D) metal dichalcogenides have attracted considerable attention for use in photoelectric devices due to their unique layer structure and strong light-matter interaction. In this paper, vertically grown SnS<sub>2</sub> nanosheets array film was synthesized by a facile chemical bath deposition (CBD). The effects of deposition time and annealing temperature on the quality of SnS<sub>2</sub> films was investigated in detail. By optimizing the preparation conditions, the SnS<sub>2</sub> array film exhibited efficient photoelectric detection performance under sunlight. Furthermore, in order to improve the performance of the photodetector based on SnS<sub>2</sub> nanosheets film, a transparent graphene film was introduced as the hole-transport layer by wet-chemical method directly transferring techniques. Graphene/SnS<sub>2</sub> nanosheets array film heterojunction photodetectors exhibit enhanced photoresponsivity. The light on/off ratio of the photodetector based on graphene/SnS<sub>2</sub> was 1.53, about 1.4 times higher than that of the pristine SnS<sub>2</sub> array films. The improved photoresponse performance suggested that the effective heterojunction between vertical SnS<sub>2</sub> nanosheets array film and graphene suppresses the recombination of photogenerated carriers. The results indicate that the graphene/SnS<sub>2</sub> heterojunction photodetectors have great potential in photodetection devices.
Project description:We report the successful growth of NiCo2S4 nanosheet films converted from NiCo2O4 nanosheet films on fluorine-doped tin oxide substrates by a low-temperature solution process. Low-cost NiCo2S4 and NiCo2O4 nanosheet films were directly used for replacing conventional Pt and NiO as counter electrodes and photocathodes, respectively, to construct all-nano p-type dye-sensitized solar cells (p-DSSCs) with high performance. Compared to Pt, NiCo2S4 showed higher catalytic activity towards the I(-)/I3 (-) redox in electrolyte, resulting in an improved photocurrent density up to 2.989 mA/cm(2), which is the highest value in reported p-DSSCs. Present p-DSSCs demonstrated a cell efficiency of 0.248 % that is also comparable with typical NiO-based p-DSSCs.
Project description:Photoanodes based on In2S3/ZnO heterojunction nanosheet arrays (NSAs) have been fabricated by atomic layer deposition of ZnO over In2S3 NSAs, which were in situ grown on fluorine-doped tin oxide glasses via a facile solvothermal process. The as-prepared photoanodes show dramatically enhanced performance for photoelectrochemical (PEC) water splitting, compared to single semiconductor counterparts. The optical and PEC properties of In2S3/ZnO NSAs have been optimized by modulating the thickness of the ZnO overlayer. After pairing with ZnO, the NSAs exhibit a broadened absorption range and an increased light absorptance over a wide wavelength region of 250-850 nm. The optimized sample of In2S3/ZnO-50 NSAs shows a photocurrent density of 1.642 mA cm-2 (1.5 V vs. RHE) and an incident photon-to-current efficiency of 27.64% at 380 nm (1.23 V vs. RHE), which are 70 and 116 times higher than those of the pristine In2S3 NSAs, respectively. A detailed energy band edge analysis reveals the type-II band alignment of the In2S3/ZnO heterojunction, which enables efficient separation and collection of photogenerated carriers, especially with the assistance of positive bias potential, and then results in the significantly increased PEC activity.
Project description:Dye-sensitised photoelectrochemical (DSPEC) cells have emerged in recent years as a route to solar fuel production. However, fuel-forming photocathodes are presently limited by photo-corrodible narrow band gap semiconductors or the small range of available wide bandgap p-type semiconductors such as NiO that display low performance with dyes. Here, we introduce CuCrO2 as a suitable p-type semiconductor for visible light-driven H2 generation upon co-immobilisation of a phosphonated diketopyrrolopyrrole dye with a Ni-bis(diphosphine) catalyst. The hybrid CuCrO2 photocathode displays an early photocurrent onset potential of +0.75 V vs. RHE and delivers a photocurrent of 15 μA cm-2 at 0.0 V vs. RHE in pH 3 aqueous electrolyte solution under UV-filtered simulated solar irradiation. Controlled potential photoelectrolysis at 0.0 V vs. RHE shows good stability and yields a Ni catalyst-based turnover number of 126 ± 13 towards H2 after 2 h. This precious metal-free system outperforms an analogous NiO|dye/catalyst assembly and therefore highlights the benefits of using CuCrO2 as a novel material for DSPEC applications.