Epitaxial Grown Sb2Se3@Sb2S3 Core-Shell Nanorod Radial-Axial Hierarchical Heterostructure with Enhanced Photoelectrochemical Water Splitting Performance

Se-S bonded non-metal elementary substance heterojunction activating photoelectrochemical water splitting

Non-metal elements are often merely regarded as electronic modulators, yet their intrinsic characteristics are frequently overlooked. Indeed, non-metal elements possess notable advantages in high-abundance, excellent hydrogen adsorption and the ability of active sites to be inversely activated, rendering them potential photoelectrochemical (PEC) materials. However, weak non-metal interbinding, susceptibility to photocorrosion, and high photogenerated carrier recombination rates hinder their practical applications. Herein, for the first time, we report a novel non-metal elementary substance heterojunction Se/S based on interfacial bonding engineering strategy. Atomic-level tight coupling of sulfonyl-rich sulfur quantum dots (SQDs) with selenium microtube arrays (Se-MTAs) enhances the structural stability of Se/S and introduces crucial Se-S heterointerfacial bonds, which not only endow Se/S with robust internal electronic interactions, but also provide high-speed channels for charge separation via unique bridging. Consequently, Se/S achieves optimal photocurrent density of 3.91 mA cm-2 at 0 VRHE, accompanied by long-term stability over 24 h. It is the highest value reported to date for Se-based photocathodes without co-catalyst and outperforms most metal-selenide-based photoelectrodes. Furthermore, the direct Z-scheme charge transport mechanism is exposed by in-depth spectroscopic analyses. Our work fills the gap in application of non-metal elementary substance heterojunction for PEC, poised for potential expansion into other new-energy devices.

Engineering Ultrathin CuxS Layer on Planar Sb2S3 Photocathode to Enhance Photoelectrochemical Transformation

Sb2S3 has been extensively used as light absorber for photoelectrochemical cell. However, its p-type nature may result in the formation of Schottky junction with substrates, thus hindering the collection of photogenerated holes. Herein, an ultrathin CuxS layer is successfully engineered as the bottom junction for Sb2S3 for the first time. Capitalizing on its impressive electrical properties and superior optical properties, the CuxS layer exhibits a high work function of 4.90 eV, which causes the upward band bending of p-type Sb2S3, forming a hole-transparent structure with ohmic contact. The transparency of the ultrathin CuxS layer enables back-illumination of the Sb2S3/CuxS platform, facilitating the integration of intricate catalyst layers for photoelectrochemical transformation. When modified with Pt nanoparticles, the photocurrent density reaches -5.38 mA cm-2 at 0 V vs. RHE, marking a fourfold increase compared to the photocathode without CuxS layer. When introducing a molecular hybrid TC-CoPc@carbon black, a remarkable average photocurrent density of -0.44 mA cm-2 at the overpotential of 0 V is obtained for CO2 reduction reaction, while the photocurrent density is less than -0.03 mA cm-2 without CuxS.

Fabrication of Flower-Shaped Sb2S3/Fe2O3 Heterostructures for Enhanced Photoelectrochemical Performance

Antimony sulfide (Sb2S3) has been recognized as a catalytic material for splitting water by solar energy because of its suitable narrow band gap, high absorption coefficient, and abundance of elements. However, many deep-level defects in Sb2S3 result in a significant recombination of photoexcited electron-hole pairs, weakening its photoelectrochemical performance. Here, by using a simple hydrothermal and spin-coating method, we fabricated a step-scheme heterojunction of Sb2S3/α-Fe2O3 to improve the photoelectrochemical performance of pure Sb2S3. Our Sb2S3/α-Fe2O3 photoanode has a photocurrent density of 1.18 mA/cm2 at 1.23 V vs reversible hydrogen electrode, 1.39 times higher than that of Sb2S3 (0.84 mA/cm2). In addition, our heterojunction has a lower onset potential, a higher absorbance intensity, a higher incident photon-to-current conversion efficiency, a higher applied bias photon-to-current efficiency, and a lower charge transfer resistance compared to pure Sb2S3. Based on ultraviolet photoelectron spectroscopy, we constructed a step-scheme band structure of Sb2S3/α-Fe2O3 to explain its photoelectrochemical enhancement. This work offers a promising strategy to optimize the performance of Sb2S3 photoelectrodes for solar-driven photoelectrochemical water splitting.

Epitaxial grown [hk1] oriented 2D/1D Bi2O2S/Sb2S3 heterostructure with significantly enhanced photoelectrochemical performance

Bismuth oxysulfide (Bi2O2S) is a layered material with high carrier mobility, excellent light absorption characteristic and good stability. However, there are few reports about the use of Bi2O2S in photoelectrochemical (PEC) water splitting. In this paper, Bi2O2S nanosheets (NSs) films were prepared on FTO substrates by one-step hydrothermal method, which broke the traditional powder state of Bi2O2S prepared. Based on the high lattice matching between antimony sulfide (Sb2S3) and bismuth sulfide (Bi2S3) obtained from the topological transformation of partial Bi2O2S, Sb2S3 nanorods (NRs) with [hk1] predominant orientation were epitaxially grown on the surface of Bi2O2S to establish a transport channel for rapid carrier migration. Titanium dioxide (TiO2) electron transport layer with oxygen vacancies was introduced into the back to capture and release electrons, further reducing the recombination rate. The photocurrent density of TiO2/Bi2O2S/Sb2S3-annealed photoelectrode at 1.23 V vs. RHE was 4.37 mA/cm2, which was 13.7 times that of monomer Bi2O2S. In addition, the TiO2/Bi2O2S/Sb2S3-annealed photoelectrode had lower charge transfer resistance and the IPCE value up to 48.22%. This study is of great significance for the application of Bi2O2S based photoelectrodes in the field of PEC water splitting.

Accelerate charge separation in Cu2O/MoO2 photocathode for photoelectrocatalytic hydrogen evolution

Photoelectrocatalyzing water reduction is a potential approach to building a green and sustainable society. As a benchmark photocathode, Cu2O receives much attention but faces serious charge recombination and photocorrosion. This work prepared an excellent Cu2O/MoO2 photocathode via in situ electrodeposition. A systematical study of theory and experiment demonstrates that MoO2 not only effectively passivates the surface state of Cu2O as well as accelerates reaction kinetics as a cocatalyst, but also promotes the directional migration and separation of photogenerated charge. As expected, the constructed photocathode exhibits a highly enhanced photocurrent density and an appealing energy transformation efficacy. Importantly, MoO2 can inhibit the reduction of Cu+ in Cu2O via a formed internal electric field and shows excellent photoelectrochemical stability. These findings pave the way to designing a high-activity photocathode with high stability.

Hole Storage Interfacial Regulation of Sb2Se3 Photocathode with Significantly Enhanced Photoelectrochemical Performance

Although interfacial engineering materials for antimony selenide (Sb₂Se₃) photocathodes have been intensively studied, most of the previous research has focused on the development of photogenerated electron transfer promoters. In this work, Sb₂Se₃ photocathodes are innovatively modified by using ferrihydrite (Fh), which has been widely used as a hole storage layer in photoanodes. After modifying Fh, the photocurrent density of the Sb₂Se₃ photocathode was increased from -0.27 to -1.6 mA cm^-2 at 0 V_RHE with the onset potential positive shift about 150 mV, and an impressive injection efficiency of 83.84% was achieved. The major contribution of Fh to the photoelectrochemical (PEC) performance enhancement was demonstrated by various characterization studies. The results show that the enhancement performance of PEC is largely attributed to the capture of back-migrating holes by Fh, the reduction of interfacial charge transfer resistance, and the significant increase in electrochemical active surface area (ECSA). This work presents new insights into the application of hole storage layers in Sb₂Se₃-based photocathodes.

Construction of Sb2S3/CdS/CdIn2S4 cascaded S-scheme heterojunction for improving photoelectrochemical performance

Antimony sulfide (Sb₂S₃) is a relatively abundant and environmentally friendly emerging photovoltaic material, which has been gradually applied in solar cells and photocatalysis. It has high light absorption capacity, but it suffers many deep-level defects and is prone to recombination of electron-hole pairs within itself. Here, by constructing the Sb₂S₃/CdIn₂S₄ S-scheme heterojunction, we avoided the problem that electrons and holes cannot be separated and transported effectively due to many Sb₂S₃ defects (more recombination centers), and improved its application in the field of photoelectrochemical water splitting. Meanwhile, in order to further improve the performance of Sb₂S₃/CdIn₂S₄ photoelectrode, we introduced CdS energy platform between Sb₂S₃ and CdIn₂S₄ to form a Sb₂S₃/CdS/CdIn₂S₄ cascaded S-scheme heterojunction. Compared with Sb₂S₃ monomer, Sb₂S₃/CdS/CdIn₂S₄ had higher absorbance intensity, IPCE value, ABPE value, and lower charge transfer resistance. In addition, the photocurrent density of the Sb₂S₃/CdS/CdIn₂S₄ photoelectrode was about 4.20 mA/cm² (1.23 V vs. RHE), which was 1.3 times higher than that of the Sb₂S₃/CdIn₂S₄ photoelectrode (3.29 mA/cm²) and 3.2 times higher than that of monomer Sb₂S₃ photoelectrode (1.32 mA/cm²). This method offers new prospects for optimizing the performance of antimony chalcogenides photoelectrodes for photoelectrochemical water splitting.