Towards Highly Efficient Chalcopyrite Photocathodes for Water Splitting: The Use of Cocatalysts beyond Pt

Charge Carrier Separation Enhancement Mechanism in Eco-Friendly CZTSSe/(Zn, Sn)O Thin-Film Photocathodes for Highly Efficient Solar-To-Hydrogen Evolution

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe)-based photocathodes present promising solutions for solar hydrogen evolution, owing to their non-toxic, cost-effective nature and exceptional photoelectrochemical (PEC) properties. Traditionally, the development of CZTSSe-based photocathodes for PEC water splitting have utilized CdS as the electron transport layer (ETL) owing to its favorable band alignment with the CZTSSe light-absorbing thin film. However, its environmental concerns pose a significant challenge. Therefore, it is crucial to identifying an eco-friendly ETL that ensures effective band alignment with kesterite materials. In this study, the Zn/Sn ratio and the thickness of the (Zn,Sn)O buffer layer is optimized to fabricate a Cd-free CZTSSe/(Zn,Sn)O/TiO₂/Pt photocathode. This design not only promotes environmental safety but also establishes optimal spike-like band alignments with the CZTSSe thin film. The optimized photocathode demonstrates excellent charge carrier separation and transfer, resulting in a photocurrent density of 29.80 mA cm- 2 at 0 VRHE and a half-cell solar-to-hydrogen (HC-STH) conversion efficiency of 4.0% in a 0.5 M H₂SO₄ electrolyte. As research continues to optimize the alternative materials, Cd-free CZTSSe/(Zn, Sn)O-based photocathodes along with their eco-friendly nature hold great promise for achieving competitive efficiencies in sustainable solar-to-hydrogen energy applications.

Organic Semiconductor-BiVO4 Tandem Devices for Solar-Driven H2O and CO2 Splitting

Photoelectrochemical (PEC) devices offer a promising platform toward direct solar light harvesting and chemical storage through artificial photosynthesis. However, most prototypes employ wide bandgap semiconductors, moisture-sensitive inorganic light absorbers, or corrosive electrolytes. Here, the design and assembly of PEC devices based on an organic donor-acceptor bulk heterojunction (BHJ) using a carbon-based encapsulant are introduced, which demonstrate long-term H2 evolution and CO2 reduction in benign aqueous media. Accordingly, PCE10:EH-IDTBR photocathodes display long-term H2 production for 300 h in a near-neutral pH solution, whereas photocathodes with a molecular CO2 reduction catalyst attain a CO:H2 selectivity of 5.41±0.53 under 0.1 sun irradiation. Their early onset potential enables the construction of tandem PCE10:EH-IDTBR - BiVO4 artificial leaves, which couple unassisted syngas production with O2 evolution in a reactor completely powered by sunlight, sustaining a 1:1 ratio of CO to H2 over 96 h of operation.

Gamma-irradiated stibnite thin films set a remarkable benchmark performance for photoelectrochemical water splitting

The study sets out to show the positive impact of sulfur vacancy engineering on the structural, morphological, optical, electrical, and photoelectrochemical (PEC) properties of Sb2S3 films synthesized using the spin coating technique. The produced films were exposed to γ-irradiation with different doses from 0 to 20 kGy. We have demonstrated the formation of sulfur vacancies and loss of oxygen content in the irradiated samples. XRD measurements revealed that all films exhibit a polycrystalline structure, and the crystallite size increases with the rising radiation dose, reaching the highest value of 87.4 nm measured for the Sb2S3 film irradiated with 15 kGy. The surface roughness of the irradiated samples increases with increasing γ-irradiation dose. The increase in surface roughness not only raises the active sites but enhances the conductivity of the Sb2S3 material as well. The wettability properties of the irradiated films were affected by γ-irradiation doses and the sample irradiated with 15 kGy exhibited the lowest hydrophobicity compared to others. The Hall measurements reveal that irradiated samples exhibit p-type semiconductor behavior. The optical band gap decreased progressively from 1.78 eV to 1.60 eV up to the irradiation dose of 15 kGy and slightly increased thereafter. The irradiated sample with 15 kGy showed a maximum photocurrent density of ca. 1.62 mA cm-2 at 0 V vs. reverse hydrogen electrode (RHE) under AM 1.5 G illumination with applied bias photon-to-current efficiency (ABPE) of 0.82% at 0.47 V vs. RHE, suggesting superior PEC water splitting performance compared to other samples. At 0 V vs. RHE and 648 nm, the incident photon current efficiency (IPCE) and absorbed photon current efficiency (APCE) of the photocathode irradiated with 15 kGy are significantly higher than those of the other photocathodes with values of 9.35% and 14.47%, respectively. Finally, Mott-Schottky measurement was also performed on all photocathodes to estimate their acceptor density and flat band potential.

Coating of gallium-based liquid metal particles with molybdenum oxide and oxysulfide for electronic band structure modulation

Liquid metal (LM) droplets are now used in many applications including catalysis, sensing, and flexible electronics. Consequently, the introduction of methods for on-demand alternating electronic properties of LMs is necessary. The active surface of LMs provides a unique environment for spontaneous chemical reactions that enable the formation of thin layers of functional materials for such modulations. Here, we showed the deposition of n-type MoO_x and MoO_xS_y semiconductors on the surface of EGaIn LM droplets under mechanical agitation to successfully modulate their electronic structures. The "liquid solution"-"liquid metal" interaction resulted in the formation of oxide and oxysulfide layers on the surface of LM droplets. The comprehensive study of electronic and optical properties revealed a decrease in the band gap of the droplets after surface decoration with MoO_x and MoO_xS_y, leading to deeper n-type doping of the materials. This method provides a facile procedure for engineering the electronic band structure of LM-based composites when they are necessary for various applications.