Amorphous materials can markedly enhance the active site amount and optimize the adsorption and desorption of reactants owing to the special structural characteristics of large numbers of randomly oriented bonds and surface-exposed defects. Therefore, many amorphous electrocatalysts have emerged for effectively catalyzing water splitting. Considering the advancement of novel in-situ techniques and theoretical density functional theory calculations, significant progress emerging in amorphous electrocatalysts for water splitting needs to be summarized urgently. Herein, the recent progress of amorphous catalyst materials in water splitting has been systematically reviewed, emphasizing key issues of synthesis methods, stabilization strategies, performance evaluation, mechanistic understanding, integrated experiments, and theoretical studies in water splitting, including hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting. This study focuses on these topics to present the most updated results and the perspectives and challenges for the future development of amorphous electrocatalysts toward water splitting.

Although photogenerated hydroxyl radicals can oxidize CO without H₂ consumption, the nonselective collision severely lowers photocatalytic photon utilization. We here demonstrate that electronic state modification of TiO₂ resulted from magnesium doping can promote hydroxyl radical generation by weakening the adsorption of oxygen species and facilitating semiconductor-cocatalyst interfacial electron transfer. Importantly, the partial deprivation of electronic cloud from cationic sites can strengthen σ-donation and π-backdonation that synergistically promote the electrostatic interaction for aggregating CO in the vicinity of semiconductor. The resulted photocatalyst thus exhibits growing superiority over common counterpart in target reaction as CO concentration lowers. By these merits, CO in H₂ stream can be reduced to < 1 × 10^-6 with efficient photon utilization.

The simultaneous utilization of photogenerated electrons and holes in one cooperative photoredox system for the dehydrocoupling of thiols into value-added disulfides and clean hydrogen (H₂) fuel meets the development criteria of green chemistry. Herein, we report the synthesis and application of cocatalyst PdS decorated ZnIn₂S₄ (PdS-ZIS) composites for photocatalytic coupling of thiols into disulfides and H₂ evolution under visible light irradiation. The superior photocatalytic performance over PdS-ZIS composites compared with blank ZIS is attributed to the function of PdS as oxidation cocatalyst, which dramatically promotes the separation and transfer of photogenerated charge carriers due to its excellent hole trapping ability. In-situ Fourier transform infrared spectra reveal the dynamic variation of reactants on the catalyst surface. Electron paramagnetic resonance technology confirms that sulfur-centered radicals are the key reaction intermediates in this coupling process. Moreover, the application of PdS-ZIS composites to the dehydrocoupling of various thiols with different substituent groups into the corresponding S-S coupling products has been demonstrated to be practicable. This work is expected to offer insights into the rational design of cocatalyst-decorated semiconductor photocatalysts with efficient utilization of photogenerated electrons and holes for the co-production of high-value chemicals and clean H₂ energy in a cooperative photoredox catalysis process.

Limited solar light harvesting, sluggish charge transfer kinetics, and inferior affinity for adsorbed hydrogen species (H*) severely restrict the photocatalytic hydrogen generation activity of TiO₂ photocatalysts. Herein, we present a novel TiO_2-x@C/MoO₂ Schottky junction prepared via a simple one-step in situ phase-transition-regulation strategy. Crucially, the abundant oxygen vacancies in TiO_2-x@C/MoO₂ narrow the bandgap and introduce defects to improve the photoresponse. The strongly bonded carbon layer not only serves as a fast charge-transport channel to improve the interlayer charge transfer efficiency but also protects oxygen vacancies from oxidation. Moreover, the Schottky barrier effectively impairs the recombination of electrons and holes and promotes the utilization of photogenerated electrons. Furthermore, the MoO₂ cocatalyst optimizes the Gibbs free energy for H₂ evolution. As a result of the favorable synergy, the resulting TiO_2-x@C/MoO₂ presents a significantly enhanced photocatalytic H₂ production rate of 506 μmol g^-1 h^-1 compared to those of TiO_2-x and TiO_2-x@C (125.5- and 15.8-times larger, respectively). Moreover, outstanding stability over 27 h was achieved because of the protection provided by the surface carbon layer. This ingenious design and facile synthetic strategy offer exciting avenues for the design of strongly coupled Schottky junction photocatalysts for efficient solar-to-chemical conversions.

Regulation of the atomic distribution is crucial for the development of atomically dispersed electrocatalysts. In this study, atomic Ru coordinated by channel ammonia in V-doped tungsten bronze (Ru/V-NHWO, Ru 0.44 wt%, V 0.45 wt%) was used as a high-performance catalyst for the hydrogen evolution reaction (HER), demonstrating remarkable mass activity in a wide pH range. Atomic Ru with a regulated spatial distribution and electronic structure was achieved owing to its unique coordination with the ammonia species in the hexagonal channels of V-NHWO. V doping in NHWO led to enhanced intrinsic activity and conductivity. Theoretical calculations revealed that the multichannel, vertically integrated Ru sites in the V-doped channels, as well as the coexisting Ru sites without multichannels or V-doping, improved the free energy of water dissociation and hydrogen sorption, which boosted the HER activity. Our study paves a new way for constructing atomically dispersed materials with a regulated spatial distribution for diverse applications.

Catalysts play a vital role in photocatalytic water-splitting by converting solar energy into storable chemical energy. In this study, we successfully synthesized an HCN/HEA heterostructure by rationally combining the Pt₁₈Ni₂₆Fe₁₅Co₁₄Cu₂₇ nano-high-entropy alloy (HEA) as an effective cocatalyst with protonated g-C₃N₄ (HCN) nanosheets, via an electrostatic self-assembly method. The resulting HCN/HEA exhibited remarkable performance in both photocatalytic H₂ production and selective oxidation of benzyl alcohol to benzaldehyde. The integration of HEA into HCN leads to the formation of Schottky junctions, which can significantly accelerate charge migration and reduce the recombination of charge carriers. Further investigations using in situ surface photovoltage imaging demonstrated that the reducing cocatalyst HEA can act as a photogenerated electron trap. The best HCN/HEA heterojunction exhibited excellent photocatalytic hydrogen production activity, reaching 2.4 mmol g^-1 h^-1 and an impressive benzaldehyde production rate of 5.44 mmol g^-1 h^-1. These values were 958 and 6.6 times higher than those achieved with pristine HCN, respectively. This study offers promise for the rational design of high-performance cocatalysts to improve the transport, separation, and utilization of light-release charge carriers.

The development of highly active, economical, and robust bifunctional photocatalysts is a priority for sustainable photocatalytic water remediation. Inadequately available reactive sites and sluggish interface photocarrier transfer and separation remain significant challenges in the photoreaction progress. In this study, the Fe-containing metal-organic framework (MOF) MIL-101(Fe) was integrated with BiOBr microspheres to form a competent S-scheme heterostructure for the photocatalytic mitigation of Cr(VI) and enrofloxacin (ENR) antibiotics. The optimal MIL-101(Fe)/BiOBr exhibited the highest photoactivity, with 99.4% of Cr(VI) and 84.4% of ENR eliminated upon visible-light illumination in a single-pollutant system. The photoactivity of MIL-101(Fe)/BiOBr in the decontamination of the Cr(VI)-ENR co-existence system exhibited a substantial enhancement when compared to that in a single system, owing to the improved utilization of electrons and holes resulting from the synergism between Cr(VI), ENR, and the photocatalyst. The enhanced photoactivity is attributed to two aspects: (1) the incorporation of MIL-101(Fe) results in an increased number of available reactive sites and improved solar harvesting properties; and (2) the S-scheme mechanism enables the effective spatial disassociation of photoexcited carriers and optimization of the photo-redox capability of the system. Through scavenging experiments, electron spin resonance characterization, liquid chromatography-tandem mass spectrometry analysis, and T.E.S.T. theoretical estimation, the catalytic mechanism, antibiotic degradation process, and biotoxicities of the degraded products were analyzed and confirmed. This study provides a viable strategy for building competent MOF-inorganic semiconductor S-scheme photocatalysts with superior photocatalytic decontamination performance.

Efficient metal-support interaction induced high catalysis performance plays a significant role in energy conversion reactions. Herein, two-dimensional (2D) MoSe₂ nanosheet-coupled Pt nanoparticles as efficient bi-functional catalysts were demonstrated for hydrogen production from the methanol-assisted water-splitting reaction. The oxophilic MoSe₂ component with 2D structures optimized the adsorption of CO* and H* on Pt sites as demonstrated by spectroscopic and theoretical analysis, which resulted in enhanced catalytic ability in methanol-assisted water splitting reaction. The peak current density was 2.5 times higher than that of commercial Pt/C catalyst for methanol oxidation and a small overpotential of 32 mV was demanded to achieve a current density of 10 mA cm^-2 for hydrogen evolution reaction in the methanol-containing electrolyte. When serviced as both cathode and anode, a low cell voltage of 0.66 V was required at 10 mA cm^-2, significantly lower than that of 1.75 V required for water splitting. The high performance can be attributed to the oxophilicity of MoSe₂ and their strong metal-support interaction that promoted the charge transfer and anti-CO poisoning of Pt sites. This work would be instructive for the development of novel bi-functional catalyst platforms for methanol-assisted water splitting in hydrogen production.

The high selectivity of organic ligands and metal ions that construct metal-organic frameworks (MOFs) enables considerable richness in the MOF structure and confers them with numerous potentials, rendering MOFs extremely interesting to researchers in the field of photocatalytic hydrogen evolution. However, the severe recombination of photoinduced charge carriers significantly restricts the photocatalytic performance of the MOFs. Herein, we report a porphyrin-based donor-acceptor (D-A) MOF consisting of meso-tetra(4-carboxyphenyl) porphyrin (TCPP) donor and a thieno [3,2b:20,30-d]thiophene-S,S-dioxide (BTDO) acceptor via coordination with Zn²⁺ ions, and denoted as TCPP-Zn-BTDO. The charge-transfer interaction from TCPP to BTDO broadened the light absorption range of TCPP-Zn-BTDO, with a high theoretical spectral efficiency of 69.72%. The D-A structure of TCPP-Zn-BTDO effectively enhanced the internal electric field because of its large molecular dipole, which significantly improved the charge-separation efficiency. Based on the aforementioned improvements, TCPP-Zn-BTDO showed a three-fold higher photocatalytic hydrogen evolution rate than the corresponding monocomponent MOF of TCPP-Zn without the BTDO acceptor. The D-A MOF reported in this study provides a new strategy for enhancing the photocatalytic performance of MOF.

The efficiency of direct catalytic oxidation of methane to methanol (DMTM) is significantly influenced by oxidants. However, realizing a one-pot DMTM using dioxygen remains challenging. Hydrogen peroxide is still the most frequently reported green oxidant for DMTM, with high selectivity for methanol. To gain insight into the influence of oxidants on DMTM performance, we computationally investigated the reaction mechanisms involved in DMTM using H₂O₂ at mono-copper sites in three types of Cu-exchanged zeolites with different micropore sizes. We identified the advantages and limitations of H₂O₂ as an oxidant. In contrast to the O-O bond in O₂, the O-O bond in H₂O₂ can be easily broken to produce reactive surface oxygen species, which enable the facile C-H bond activation of methane at a low temperature. However, because of the radical-like process of C-H bond activation at mono-copper sites, actualizing the preferential C-H bond activation of methane is kinetically challenging compared to that of methanol. Moreover, the lower O-H bonding energy of H₂O₂ would result in self-decomposition of H₂O₂. Despite these bottlenecks, kinetic analysis shows that improving catalysts to boost the DMTM performance using H₂O₂ is a promising approach.

The design of photocatalysts for the stable and efficient photocatalytic reduction of CO₂ without sacrificial agents remains challenging. In this study, Fe atoms were anchored on the surface of TiO₂ with atomic-level dispersion using a novel negative-pressure encapsulation and pyrolysis strategy. The photoelectrochemical test results confirmed that the introduction of single Fe atoms accelerated the separation of photogenerated carriers and enhanced the TiO₂ utilization rate of visible light. The optimal catalyst with atomically dispersed Fe showed excellent photocatalytic conversion of CO₂ to CO (48.2 μmol·g^-1·h^-1) and CH₄ (113.4 μmol·g^-1·h^-1), whereas the TiO₂ system produced only trace amounts of CO (2.7 μmol·g^-1·h^-1). The increased CO₂ adsorption energy and movement of the d-band center toward the Fermi level confirmed that single Fe sites were more favorable for the adsorption of CO₂. The differential charge density distribution of CO₂ adsorbed on the catalyst surface confirmed the rapid transfer of electrons along the Ti-O-Fe-C path, and the Gibbs free energy calculation further confirmed that the Fe sites were conducive to reducing the energy barrier required for the reaction. In addition, the key intermediate (*COOH) of CO₂ conversion to CH₄ was detected by in situ diffuse reflectance infrared Fourier transform spectroscopy, and a possible reaction pathway was proposed. This work provides an effective strategy for designing single-atom catalysts that can efficiently reduce CO₂ to high-value-added products.

Baeyer-Villiger monooxygenases (BVMOs) can catalyze the asymmetric oxidation of sulfides to valuable chiral sulfoxides, but the overoxidation of sulfoxides to undesired sulfones limits the synthetic application of BVMOs. This overoxidation is caused by insufficient substrate selectivity of BVMOs, where the desired product sulfoxide can be further oxidized. In this study, a mathematical model was constructed to quantitatively define the substrate selectivity based on the ratio of the specificity constant (k_cat/K_m) between sulfide and sulfoxide. The substrate selectivity of a pyrmetazole monooxygenase (AcPSMO) was precisely regulated using a structure-guided substrate tunnel engineering approach, which successfully minimized sulfoxide overoxidation. The sulfone content of variant F277L was less than 1% (mol/mol), compared with 65% for the wild-type, in the pyrmetazole oxidation reaction after 24 h. Molecular dynamics simulations and quantum mechanics/molecular mechanics studies showed that the altered H-bonding networks surrounding the flavin hydroperoxide (FADH-OOH) can modulate the mechanism and activity for sulfoxide oxidation. Furthermore, the redesigned mutants of AcPSMO were successfully applied for the controllable synthesis of other chiral prazole sulfoxides.

The overall photocatalytic conversion of CO₂ and H₂O to fuel and O₂ is challenging. In this study, a series of three-dimensional Tröger’s base-derived porous aromatic frameworks (3D-X-TB-PAFs (X = TEPE, TEPM, SPF)) featuring designated reaction sites and unique charge transfer properties were developed. The incorporation of V-shaped Tröger’s base (TB) units and aromatic alkynes imparts the polymers with permanent porosity, additional photon scattering cross-sections, and enhanced CO₂ adsorption/activation capabilities. Density functional theory calculations and optoelectronic measurements revealed the formation of intramolecular built-in polarization and electron-trap sites induced by TB, which modulated charge separation and customized reaction sites in collaboration with 3D networks. In addition, product allocation during the photoreduction of CO₂ was regulated by the photooxidation of H₂O. Among the as-prepared 3D-PAFs, the most efficient electron transport channel was demonstrated by the TEPE-TB-PAF with fully conjugated TEPE-T. In the absence of cocatalysts and sacrificial agents, TEPE-TB-PAF exhibits a competitive CO formation rate (194.50 μmol g^-1 h^-1) with near-unity selectivity (99.74%). Significantly, the low energy barrier for CO desorption and the high energy barrier for *CHO formation contribute to the high efficiency of TEPE-TB-PAF, as demonstrated by computational exploration and in situ diffuse reflectance infrared Fourier transform spectra. This work offers efficient building blocks for the synthesis of multifunctional organic photocatalysts and groundbreaking insights into the simultaneous enhancement of photocatalytic reactivity and selectivity.

The design of a heterogeneous structure for photocatalysts has attracted significant attention. In this study, a step-scheme (S-scheme) heterojunction was designed using an in-situ synthesis method. The resulting heterojunction comprised 3D microspheres of ZnIn₂S₄ and octahedral MOF-808 (ZnIn₂S₄/MOF-808). During this process, we investigated the impact of the scale of the ZnIn₂S₄ microspheres on performance by controlling the growth of the ZnIn₂S₄ microspheres with various scales. The maximum catalytic activity was discovered to be achieved with ZnIn₂S₄ microspheres of 6 µm when coupled with MOF-808. Compared to pure ZnIn₂S₄ and MOF-808, the fabricated S-scheme ZnIn₂S₄/MOF-808 heterojunction exhibited notably improved photocatalytic CO₂ reduction performance. The performance of the CO yield of the optimized sample could reach 8.21 μmol g^‒1 h^‒1, which was approximately 10 and 8 times higher than those of ZnIn₂S₄ (0.84 μmol g^‒1 h^‒1) and MOF-808 (1.03 μmol g^‒1 h^‒1), respectively. Moreover, ultraviolet photoelectron spectroscopy, ESR, in situ X-ray photoelectron spectroscopy, and density functional theory calculations were used to study the charge transfer mechanism of the S-scheme heterojunction. In-situ FT-IR investigation established the Carbene pathway as the source of CO production (CO₂ → CO₂^* → COOH^* → CO^* → CO). This study provides an efficient method for designing an S-scheme heterojunction for photocatalytic CO₂ reduction.

Investigating the charge-transfer behavior of photocatalysts is important to promote the photoreduction of CO₂ into solar fuels. Therefore, in this study, hybrid Ta₂O₅ nanofibers were produced through the in situ growth of freestanding NiS nanosheets. The charge separation and CO₂ photoreduction mechanisms of these nanofibers were investigated using in situ X-ray photoelectron spectroscopy and density functional theory calculations. The results suggested that the NiS@Ta₂O₅ nanohybrids formed an S-scheme heterojunction, which promoted the efficient separation of electron-hole pairs and enhanced CO₂ photoreduction. Compared to the pristine Ta₂O₅ nanofibers, the hybrid nanofibers exhibited a significantly higher CO₂-reduction rate (43.27 μmol g^-1 h^-1 for CO; 6.56 μmol g^-1 h^-1 for CH₄). In situ diffuse reflectance infrared Fourier-transform spectroscopy results confirmed the process of CO₂ hydrogenation and S-scheme charge transfer pathways in NiS@Ta₂O₅ nanohybrids.

The conversion from solar energy into storable chemical energy can be achieved through synergistic coupling of photocatalytic H₂ production and organic synthesis, during which photogenerated electrons and holes can be simultaneously utilized. Herein, we combined a zirconium-based metal-organic framework, UiO-66-NH₂, and CdS nanoparticles (NPs) to form a core-shell structure by a chemical bath method. The step-scheme (S-scheme) heterojunction exhibits both substantially enhanced selective oxidation of benzyl alcohol and efficient H₂ generation under light irradiation simultaneously. The electron transfer paths at the S-scheme heterostructure interface were investigated in depth by in situ irradiated X-ray photoelectron spectroscopy. The dynamics of carrier migration at the heterojunction were obtained through femtosecond transient absorption (fs-TA) spectroscopy. Furthermore, the evolution mechanism of benzaldehyde was revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy and electron paramagnetic resonance. This work illustrates the electron transfer mechanism of S-scheme heterojunction by fs-TA spectroscopy and provides new insights into the design of MOF/inorganic composite photocatalysts.

Transition metal single-atom catalysts have attracted considerable attention for their applicability in electrocatalytic oxygen reduction reactions (ORR), but it is still very challenging to regulate the interaction between the active sites and oxygen-containing intermediates. In this study, atomically dispersed Co-N₅ sites integrated with defective N-doped carbon (Co-N₅/DHC) were developed using a facile templating approach, followed by NH₃ treatment. NH₃ can simultaneously etch inactive amorphous substrates on the surfaces of metal sites and construct intrinsic carbon defects, thereby increasing the number of both metal and metal-free active sites. By bridging the intrinsic carbon defects and metal sites, the optimized Co-N₅/DHC catalyst exhibited significantly improved electrocatalytic ORR performance compared to the pristine Co-N_x/HC sample (cobalt-nitrogen sites anchored on heteroatom-doped carbon). Density functional calculations revealed that the strong interaction between the Co-N₅ sites and carbon defects modified the electronic localization, thus optimizing the binding energy with oxygen-containing intermediates and resulting in significantly improved ORR catalytic activity with a half-wave potential of 0.877 V. In addition, a zinc-air battery assembled with the Co-N₅/DHC as the cathode achieves a maximum power density of 160.7 mW cm^-2 and affords a specific capacity of 766.2 mA h g_Zn⁻¹.

Efficient heterogeneous catalysts play a very important role in the value-updated green hydrogen production from urea-containing wastewater. Herein, NiSe₂/MoSe₂ heterostructured catalyst with optimized interfacial electron redistribution and urea adsorption energies via a strong built-in electric field was demonstrated effective for the urea-assisted water splitting reactions. Efficient catalytic performance was found on NiSe₂/MoSe₂ hybrid microsphere owing to the combined merits such as the unique structure features, the strong synergetic coupling effects, the increased active sites, and the high amount of intrinsic Ni³⁺ species. Excellent urea oxidation activity was found to drive 10 mA cm^‒2 at the potential of 1.33 V when loaded on the glassy carbon electrode, and a cell voltage of 1.47 V was required in the NiSe₂/MoSe₂||Pt/C urea-water electrolyzer to drive 10 mA cm^‒2, about 220 mV less than that of water electrolysis, indicating a less energy consumption technique during the electrolysis. The spectroscopic and theoretical analysis revealed the effective synergy of the Ni-Se bond and Mo-Se bond that would be promising for efficient catalyst system construction.