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The oxygen evolution reaction, which involves high overpotential and slow charge-transport kinetics, plays a critical role in determining the efficiency of solar-driven water splitting. The chiral-induced spin selectivity phenomenon has been utilized to reduce by-product production and hinder charge recombination. To fully exploit the spin polarization effect, we herein propose a dual spin-controlled perovskite photoelectrode. The three-dimensional (3D) perovskite serves as a light absorber while the two-dimensional (2D) chiral perovskite functions as a spin polarizer to align the spin states of charge carriers. Compared to other investigated chiral organic cations, R -/ S -naphthyl ethylamine enable strong spin-orbital coupling due to strengthened π–π stacking interactions. The resulting naphthyl ethylamine-based chiral 2D/3D perovskite photoelectrodes achieved a high spin polarizability of 75%. Moreover, spin relaxation was prevented by employing a chiral spin-selective L -NiFeOOH catalyst, which enables the secondary spin alignment to promote the generation of triplet oxygen. This dual spin-controlled 2D/3D perovskite photoanode achieves a 13.17% of applied-bias photon-to-current efficiency. Here, after connecting the perovskite photocathode with L -NiFeOOH/ S -naphthyl ethylamine 2D/3D photoanode in series, the resulting co-planar water-splitting device exhibited a solar-to-hydrogen efficiency of 12.55%. Enhancing the efficiency of solar-driven water splitting is challenging but highly interesting. Here the authors report a dual spin-controlled 2D/3D perovskite photoelectrode that achieves 12.55% efficiency by utilizing the chiral-induced spin selectivity phenomenon.

Hydrogen production techniques based on solar-water splitting have emerged as carbon-free energy systems. Many researchers have developed highly efficient thin-film photoelectrochemical (PEC) devices made of low-cost and earth-abundant materials. However, solar water splitting systems suffer from short lifetimes due to catalyst instability that is attributed to both chemical dissolution and mechanical stress produced by hydrogen bubbles. A recent study found that the nanoporous hydrogel could prevent the structural degradation of the PEC devices. In this study, we investigate the protection mechanism of the hydrogel-based overlayer by engineering its porous structure using the cryogelation technique. Tests for cryogel overlayers with varied pore structures, such as disconnected micropores, interconnected micropores, and surface macropores, reveal that the hydrogen gas trapped in the cryogel protector reduce shear stress at the catalyst surface by providing bubble nucleation sites. The cryogelated overlayer effectively preserves the uniformly distributed platinum catalyst particles on the device surface for over 200 h. Our finding can help establish semi-permanent photoelectrochemical devices to realize a carbon-free society. Photoelectrodes made of earth-abundant materials can contribute to low-cost and carbon-free hydrogen production, but suffer from a short lifetime. Here the authors report cryogel overlayer to increase the operation time of the device by regulating evolving hydrogen bubble dynamics.

To realize practical solar hydrogen production, a low‐cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu3BiS3‐based photocathode. By exploiting the crystallographic similarities between Bi2S3 and Cu3BiS3, a one‐step solution process with two sulfur sources is used to prepare the Bi2S3–Cu3BiS3 blended interlayer. The elongated Bi2S3‐Cu3BiS3 mixed‐phase 1D nanorods atop a planar Cu3BiS3 film enable a high photocurrent density of 7.8 mA cm−2 at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 VRHE. The increased performance over the single‐phase Cu3BiS3 thin‐film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n‐type CdS layer. A solar‐to‐hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state‐of‐the‐art Mo:BiVO4 photoanode, with excellent stability exceeding 21 h. A novel solution‐processed Bi2S3–Cu3BiS3 mixed phase is fabricated for photoelectrochemical photocathodes generating high photocurrents and onset potential. By exploiting the unique dual‐sulfur‐source chemistry, unique nanostructure is obtained. The Bi2S3–Cu3BiS3 photocathode demonstrates synergetic effects of enhanced light absorption and superior charge transport, enabling 2.33% unassisted solar‐to‐hydrogen conversion efficiency when coupled with Mo:BiVO4 photoanode.

To achieve a high solar‐to‐hydrogen (STH) conversion efficiency, delicate strategies toward high photocurrent together with sufficient onset potential should be developed. Herein, an SnS semiconductor is reported as a high‐performance photocathode. Use of proper sulfur precursor having weak dipole moment allows to obtain high‐quality dense SnS nanoplates with enlarged favorable crystallographic facet, while suppressing inevitable anisotropic growth. Furthermore, the introducing Ga2O3 layer between SnS and TiO2 in SnS photocathodes efficiently improves the charge transport kinetics without charge trapping. The SnS photocathode reveals the highest photocurrent density of 28 mA cm−2 at 0 V versus the reversible hydrogen electrode. Overall solar water splitting is demonstrated for the first time by combining the optimized SnS photocathode with a Mo:BiVO4 photoanode, achieving a STH efficiency of 1.7% and long‐term stability of 24 h. High performance and low‐cost SnS photocathode represent a promising new material in the field of photoelectrochemical solar water splitting. Crystal facet control dramatically enhances both the photocurrent density of SnS photocathodes to 28 mA cm−2 at 0 VRHE and the onset potential to 0.4 VRHE owing to the extended (101) facet. By combining the photocathode with a Mo:BiVO4 photoanode, unbiased solar water splitting is successfully demonstrated with bench‐mark efficiency (≈1.7%) and long‐term stability of 24 h.

Oxygen evolution reaction (OER) as a half‐anodic reaction of water splitting hinders the overall reaction efficiency owing to its thermodynamic and kinetic limitations. Iodide oxidation reaction (IOR) with low thermodynamic barrier and rapid reaction kinetics is a promising alternative to the OER. Herein, we present a molybdenum disulfide (MoS2) electrocatalyst for a high‐efficiency and remarkably durable anode enabling IOR. MoS2 nanosheets deposited on a porous carbon paper via atomic layer deposition show an IOR current density of 10 mA cm–2 at an anodic potential of 0.63 V with respect to the reversible hydrogen electrode owing to the porous substrate as well as the intrinsic iodide oxidation capability of MoS2 as confirmed by theoretical calculations. The lower positive potential applied to the MoS2‐based heterostructure during IOR electrocatalysis prevents deterioration of the active sites on MoS2, resulting in exceptional durability of 200 h. Subsequently, we fabricate a two‐electrode system comprising a MoS2 anode for IOR combined with a commercial Pt@C catalyst cathode for hydrogen evolution reaction. Moreover, the photovoltaic–electrochemical hydrogen production device comprising this electrolyzer and a single perovskite photovoltaic cell shows a record‐high current density of 21 mA cm–2 at 1 sun under unbiased conditions. A MoS2 catalyst is uniformly deposited on carbon paper using the atomic layer deposition process. The MoS2‐based heterostructure anode for iodide oxidation reaction (IOR) combined with a Pt@C cathode for hydrogen evolution reaction delivers 10 mA cm−2 at a low cell voltage of 0.66 V. By connecting this electrolyzer with a single perovskite photovoltaic cell, the resulting photovoltaic–electrochemical device coupled with IOR produces a record‐high current density of 21 mA cm−2 without external bias.

Photovoltaic (PV)‐assisted photoelectrochemical (PEC) tandem cells with elevated hydrogen (H2) production rates are a practical approach for carbon‐dioxide‐free, green H2 production. A semitransparent single‐cell‐based wide‐bandgap perovskite solar cell (PSC) coupled with an Si photocathode provides sufficient potential for H2 generation when combined with a sulfate oxidation reaction. While energetically favorable ZnO as an electron transport layer (ETL) increases the V OC to 1.19 V for mixed‐halide perovskite, phase decomposition is induced when Br ions contacted the ZnO ETL. The SnO2 interlayer shows improved passivation, superior operational stability, and excellent performance among the various atomic layer deposited metal oxides tested. Furthermore, the resulting semitransparent PSC demonstrates reproducibility of its enhanced PV parameters (i.e., V OC 1.17 ± 0.01 V, FF = 76.78 ± 1.39%, and PCE = 11.95 ± 1.13%) due to better interface quality. The precise calculation of light absorption from both PV and Si for the overall tandem device leads to optimized light harvesting in the top and bottom electrodes, maximizing H2 production. Overall, the PV‐PEC device incorporated with a chemically stable semitransparent top PSC and bottom Si photocathode allows to accomplish stable H2 production at 11.1 mA cm−2 under unbiased conditions. A hydrogen production system involving ZnO ETL‐based semitransparent PSC and Si photocathode combined with SOR is presented. The device operational stability for ZnO ETL‐based PSC is sufficiently extended by introducing an ALD‐derived SnO2 interlayer. The well‐designed PV‐PEC tandem cell demonstrates a remarkable hydrogen‐generating photocurrent density of 11.1 mA cm−2.

Perovskite-based solar water splitting systems are promising candidates for addressing environmental challenges, exceeding the commercialization efficiency of solar-to-hydrogen (STH) at >10%. However, the operational stability remains suboptimal due to insufficient in situ/operando insights into charge carrier dynamics. Here, we investigate the role of charge accumulation on operational stability through operando catalytic modulation via near-infrared (NIR) toggling on a photothermal catalyst. Electrochemical analyses under operando NIR toggling demonstrate enhanced hydrogen evolution reaction kinetics and reduced charge recombination. In situ analyses confirm that reduced charge accumulation suppresses ion migration in the perovskite layer, thereby enhancing operational stability. The NIR-irradiated cathode delivers a photocurrent density of 25.48 mA cm , maintaining 90% of its initial photocurrent density at 0 V for 310 h. A parallelly-illuminated coplanar system with NIR-irradiated perovskite-based water splitting cathode operates without bias, achieving a STH efficiency of 15.18%, retaining 70% of their initial performance for 115 h.

To realize practical solar hydrogen production, a low‐cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu 3 BiS 3 ‐based photocathode. By exploiting the crystallographic similarities between Bi 2 S 3 and Cu 3 BiS 3 , a one‐step solution process with two sulfur sources is used to prepare the Bi 2 S 3 –Cu 3 BiS 3 blended interlayer. The elongated Bi 2 S 3 ‐Cu 3 BiS 3 mixed‐phase 1D nanorods atop a planar Cu 3 BiS 3 film enable a high photocurrent density of 7.8 mA cm −2 at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 V RHE . The increased performance over the single‐phase Cu 3 BiS 3 thin‐film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n‐type CdS layer. A solar‐to‐hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state‐of‐the‐art Mo:BiVO 4 photoanode, with excellent stability exceeding 21 h.

To realize practical solar hydrogen production, a low-cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu3 BiS3 -based photocathode. By exploiting the crystallographic similarities between Bi2 S3 and Cu3 BiS3 , a one-step solution process with two sulfur sources is used to prepare the Bi2 S3 -Cu3 BiS3 blended interlayer. The elongated Bi2 S3 -Cu3 BiS3 mixed-phase 1D nanorods atop a planar Cu3 BiS3 film enable a high photocurrent density of 7.8 mA cm-2 at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 VRHE . The increased performance over the single-phase Cu3 BiS3 thin-film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n-type CdS layer. A solar-to-hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state-of-the-art Mo:BiVO4 photoanode, with excellent stability exceeding 21 h.To realize practical solar hydrogen production, a low-cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu3 BiS3 -based photocathode. By exploiting the crystallographic similarities between Bi2 S3 and Cu3 BiS3 , a one-step solution process with two sulfur sources is used to prepare the Bi2 S3 -Cu3 BiS3 blended interlayer. The elongated Bi2 S3 -Cu3 BiS3 mixed-phase 1D nanorods atop a planar Cu3 BiS3 film enable a high photocurrent density of 7.8 mA cm-2 at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 VRHE . The increased performance over the single-phase Cu3 BiS3 thin-film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n-type CdS layer. A solar-to-hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state-of-the-art Mo:BiVO4 photoanode, with excellent stability exceeding 21 h.

Oxygen evolution reaction (OER) as a half‐anodic reaction of water splitting hinders the overall reaction efficiency owing to its thermodynamic and kinetic limitations. Iodide oxidation reaction (IOR) with low thermodynamic barrier and rapid reaction kinetics is a promising alternative to the OER. Herein, we present a molybdenum disulfide (MoS 2 ) electrocatalyst for a high‐efficiency and remarkably durable anode enabling IOR. MoS 2 nanosheets deposited on a porous carbon paper via atomic layer deposition show an IOR current density of 10 mA cm –2 at an anodic potential of 0.63 V with respect to the reversible hydrogen electrode owing to the porous substrate as well as the intrinsic iodide oxidation capability of MoS 2 as confirmed by theoretical calculations. The lower positive potential applied to the MoS 2 ‐based heterostructure during IOR electrocatalysis prevents deterioration of the active sites on MoS 2 , resulting in exceptional durability of 200 h. Subsequently, we fabricate a two‐electrode system comprising a MoS 2 anode for IOR combined with a commercial Pt@C catalyst cathode for hydrogen evolution reaction. Moreover, the photovoltaic–electrochemical hydrogen production device comprising this electrolyzer and a single perovskite photovoltaic cell shows a record‐high current density of 21 mA cm –2 at 1 sun under unbiased conditions.