Efficient Acidic Photoelectrochemical Water Splitting Enabled by Ru Single Atoms Anchored on Hematite Photoanodes

Enhanced Charge Transportation in Type II WO3/ZnWO4 Nanoflakes for Boosting Saline Water-splitting Reaction

Photoelectrochemical (PEC) water-splitting is an energy-efficient and eco-friendly technique to produce green hydrogen (H2). Here, WO3 is synthesized for saline water-splitting reaction. Initially, the activity of WO3 is enhanced through morphology tuning. Nanoparticles (NPs), thick nanosheets (TSs), and nanoflakes (NFs) of WO3 are synthesized, and their PEC activity is determined. The NFs show a photocurrent density of 1.53 mA/cm2 at 1.2 V vs. Ag/AgCl, whereas TSs and NPs can generate 1.17 mA/cm2 and 1.07 mA/cm2 at 1.2 V vs. Ag/AgCl, respectively. The low charge transportation rate inhibits the PEC performance of these NFs in water-splitting reactions. To mitigate this problem, the type-II heterojunction is constructed with optimized deposition of ZnWO4 on WO3, which favors the migration of charge-carriers in opposite directions, facilitating the charge-carrier separation and eventually enhancing the PEC activity. The optimized heterojunction shows a photocurrent density 1.5 times greater than bare WO3 and 2.4 times enhanced carrier density, 2.16×1021 cm-3. The heterostructure's rapid OCP decay and higher charge injection efficiency indicate an improved charge transport capability, the primary driving force for enhanced PEC activity. The stability of WO3/ZnWO4 is studied for one hour.

Surface Nd Sites Boost Charge Transfer of Fe2O3 Photoanodes for Enhanced Solar Water Oxidation

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising technology for sustainable energy generation. In this work, we introduce Nd sites boost the PEC performance of Fe2O3 photoanodes through a precise gas-phase cation exchange process, which substitutes surface Fe atoms with Nd. The incorporation of Nd significantly enhances charge transfer properties, increases carrier concentration, and reduces internal resistance, leading to a substantial increase in photocurrent density from 0.44 to 0.92 mA cm-2 at 1.23 VRHE. Further enhancement of catalytic activity was achieved by depositing a NiCo(OH)x layer and a photocurrent density of 1.15 mA cm-2 at 1.23 VRHE were obtained. Theoretical calculations corroborate these experimental results, revealing that Nd doping narrows the bandgap, improves charge separation efficiency, and lowers the reaction potential barrier, thereby accelerating water oxidation kinetics. These findings underscore the effectiveness of surface cation exchange and targeted metallic element doping in overcoming the intrinsic limitations of Fe2O3, providing a viable pathway for developing high-performance PEC systems for efficient hydrogen production.

Nanoencapsulated Optical Fiber-Based PEC Microelectrode: Highly Sensitive and Specific Detection of NT-proBNP and Its Implantable Performance

Microelectrodes offer exceptional sensitivity, rapid response, and versatility, making them ideal for real-time detection and monitoring applications. Photoelectrochemical (PEC) sensors have shown great value in many fields due to their high sensitivity, fast response, and ease of operation. Nevertheless, conventional PEC sensing relies on cumbersome external light sources and bulky electrodes, hindering its miniaturization and implantation, thereby limiting its application in real-time disease monitoring. To overcome these limitations, we developed a nanoencapsulated optical fiber (OF)-based PEC microelectrode. The microelectrode features TiO2/CdS nanocrystals and bis (2,2'-bipyridine) (10-methylphenanthroline [3,2-a:2'3'-c] pyridine ruthenium(II) dichloride ([Ru(bpy)2dppz]2+) @dsDNA/Au@epigallocatechin gallate nanoparticle (EGCG NP) layers. And its application for the detection of N-terminal pro-brain natriuretic peptide (NT-proBNP) as a biomarker of cardiovascular diseases was explored. An extensive linear range of 1-5000 pg mL-1 combined with a low detection limit of 0.36 pg mL-1 was achieved. This range covers not only the recommended threshold for excluding cardiovascular diseases in the clinical diagnosis of individuals across all age groups but also the prognostic target value. The sensor exhibited excellent selectivity and stability and notable labeling recovery capability in serum tests. Critically, the sensor successfully discriminated the alterations in NT-proBNP secretion levels within human smooth muscle cells, comparing pre- and poststimulation by platelet-derived growth factor-BB. Even more significantly, the skin puncture experiment conducted in mice demonstrated the remarkable implantability and biological compatibility of the OF-PEC microelectrode. This addresses critical challenges commonly faced by microelectrodes when used as implanted devices, such as minimizing invasive trauma, mitigating inflammation, and preventing biofouling, thereby firmly establishing their suitability for the development of advanced implantable sensing devices. Therefore, the present OF microelectrode PEC biosensor is not only cost-effective, easy to operate, and miniaturized but also holds significant potential for enabling more precise, more minimally invasive, and continuous monitoring of biological markers without causing inflammation. This capability is crucial for early disease detection, tracking disease progression, and facilitating personalized treatment strategies, which expands the practical application of PEC sensors.

Calcium single atoms stabilized by nitrogen coordination in metal-organic frameworks as efficient solid base catalysts

Considerable attention has been paid to the preparation of single-atom solid base catalysts (SASBCs) owing to their high activity and maximized utilization of basic sites. At present, the reported fabrication methods of SASBCs, such as two-step reduction strategy and sublimation capture strategy, require high temperature. Such a high activation temperature is easy to cause the sublimation loss of alkali or alkaline earth metal atoms and destructive to the support structure. Herein, a new SASBC, Ca1/UiO-67-BPY, is fabricated, in which the alkaline earth metal Ca sites are immobilized onto N-rich metal-organic framework UiO-67-BPY at room temperature. The results show that the atomic configuration of Ca single atoms is coordinated by two N atoms in the framework. The obtained Ca SASBC possesses ordered structure and exhibits high product yield of 87.2% in the Knoevenagel reaction between benzaldehyde and malononitrile. Furthermore, thanks to the Ca single atoms sites anchored on UiO-67-BPY, the Ca1/UiO-67-BPY catalyst also shows good stability during cycles. This work might offer new insight in designing SASBCs for different base-catalyzed reactions.

Robust construction of CeNi quantum dots/Ni-MOL nanosheets for superior photocatalytic CO2 reduction

Since the intensification of global environmental pollution and energy shortages, photocatalytic CO2 reduction reaction (CO2RR) has emerged as a promising strategy to convert solar energy into clean chemical energy. Herein, we construct a robust and efficient heterojunction construction photocatalyst for CO2RR, composed of the highly reactive CeNi quantum dots (CeNi QDs) and nickel metal-organic layer (Ni-MOL) ultrathin nanosheets. This design facilitates the rapid separation of photogenerated charge carriers, as confirmed by X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and other characterizations. Mechanistic studies with in situ diffuse reflectance Fourier transform infrared spectroscopy (in situ DRIFTS) and the d-band center calculation indicate that the propensity of photocatalyst for CO2 absorption and CO desorption, leading to high performance and selectivity. The optimized loading amount of CeNi quantum dots and modified structure result in a CO yield of 30.53 mmol·g-1 within 6 h under irradiation. This work not only paves a new and convenient way for developing high-activity quantum dot materials for CO2RR but also exploits novel avenues to fabricate more heterojunction composites for solar energy conversion.

Copper Sulfide based Photocatalysts, Electrocatalysts and Photoelectrocatalysts: Innovations in Structural Modulation and Application

Copper sulfides (CuxS, 1 ≤ x ≤ 2) are notable for their unique photoelectric properties and potential applications, particularly in photo/electrocatalysis. These materials are valued for their tunable band gap, near-infrared optical characteristics, and plasmonic resonance effects. However, challenges such as low catalytic activity and limited stability impede their practical applications. This review addresses these issues by exploring advanced strategies for electronic structure modulation, including atomic doping, shape alteration, heterojunction construction, and defect introduction to enhance catalytic efficiency. A detailed analysis of the optical and electrical properties of CuxS across various stoichiometric ratios and crystal structures is provided, offering a comprehensive overview of their applications in photocatalysis, electrocatalysis, and photo/electrocatalysis. Additionally, the review synthesizes current knowledge and highlights the potential of these strategies to optimize CuxS-based photo/electrocatalysts, proposing future research directions to bridge the gap between theoretical studies and practical applications. This work underscores the importance of CuxS in photo/electrocatalysis and aims to inspire further innovation and exploration in this field, emphasizing its significance in material science and engineering.

The breakthrough of oxide pathway mechanism in stability and scaling relationship for water oxidation

An in-depth understanding of electrocatalytic mechanisms is essential for advancing electrocatalysts for the oxygen evolution reaction (OER). The emerging oxide pathway mechanism (OPM) streamlines direct O-O radical coupling, circumventing the formation of oxygen vacancy defects featured in the lattice oxygen mechanism (LOM) and bypassing additional reaction intermediates (*OOH) inherent to the adsorbate evolution mechanism (AEM). With only *O and *OH as intermediates, OPM-driven electrocatalysts stand out for their ability to disrupt traditional scaling relationships while ensuring stability. This review compiles the latest significant advances in OPM-based electrocatalysis, detailing design principles, synthetic methods, and sophisticated techniques to identify active sites and pathways. We conclude with prospective challenges and opportunities for OPM-driven electrocatalysts, aiming to advance the field into a new era by overcoming traditional constraints.

Inducing Intermolecular Oxygen Coupling by Introducing S and FeOOH on Co(OH)2 Nanoneedle Arrays for Industrial Water Oxidation

The design of electrocatalysts for oxygen evolution reaction (OER) remains a limitation of industrial hydrogen production by electrolysis of water. Excellent and stable OER catalysts can be developed by activating lattice oxygen and changing the reaction path. Herein, S and FeOOH on the Co(OH)2 nanoneedle arrays are introduced to construct a heterostructure (S-FeOOH/Co(OH)2/NF) as a proof of concept. Theoretical calculations and experimental suggest that the Co-O-Fe motif formed at the heterogeneous interface with the introduction of FeOOH, inducing electron transfer from Co to Fe, enhancing Co─O covalency and reducing intramolecular charge transfer energy, thereby stimulating direct intramolecular lattice oxygen coupling. Doping of S in FeOOH further accelerates electron transfer, improves lattice oxygen activity, and prevents dissolution of FeOOH. Consequently, the overpotential of S-FeOOH/Co(OH)2/NF is only 199 mV at 10 mA cm-2, and coupled with the Pt/C electrode can be up to 1 A cm-2 under 1.79 V and remain stable for over 120 h in an anion exchange membrane water electrolyzer (AEMWE). This work proposes a strategy for the design of efficient and stable electrocatalysts for industrial water electrolysis and promotes the commercialization of AEMWE.

Exploiting the Bragg Mirror Effect of TiO2 Nanotube Photonic Crystals for Promoting Photoelectrochemical Water Splitting

Exploiting the Bragg mirror effect of photonic crystal photoelectrode is desperately desired for photoelectrochemical water splitting. Herein, a novel TiO2 nanotube photonic crystal bi-layer structure consisting of a top nanotube layer and a bottom nanotube photonic crystal layer is presented. In this architecture, the photonic bandgap of bottom TiO2 nanotube photonic crystals can be precisely adjusted by modulating the anodization parameters. When the photonic bandgap of bottom TiO2 nanotube photonic crystals overlaps with the electronic bandgap of TiO2, the bottom TiO2 nanotube photonic crystal layer will act as a Bragg mirror, leading to the boosted ultraviolet light absorption of the top TiO2 nanotube layer. Benefiting from the promoted UV light absorption, the TiO2 NT-115-NTPC yields a photocurrent density of 1.4 mA/cm2 at 0.22 V vs. Ag/AgCl with a Faradic efficiency of 100%, nearly two times higher than that of conventional TiO2 nanotube arrays. Furthermore, incident photon-to-current conversion efficiency is also promoted within ultraviolet light region. This research offers an effective strategy for improving the performance of photoelectrochemical water splitting through intensifying the light-matter interaction.

Vacancy-Induced Symmetry Breaking in Titanium Dioxide Boosts the Photocatalytic Hydrogen Production from Methanol Aqueous Solution

The key to optimizing photocatalysts lies in the efficient separation and oriented migration of the photogenerated carriers. Herein, we report that breaking continuous TiO6 tetragonal (D4h) symmetry in titanium dioxide material by oxygen vacancy engineering could induce a dipole field within the bulk phase and thus facilitate the separation and transfer of photogenerated electron-hole pairs. After further loading of Cu single-atom co-catalysts, the obtained catalyst attained a hydrogen (H2) yield rate of 15.84 mmol g-1 h-1 and a remarkable apparent quantum yield of 12.67% at 385 nm from methanol aqueous solution. This catalyst also demonstrated impressive stability for at least 24 h during the photocatalytic tests. The innovative concept of producing dipole fields in semiconductors by breaking the crystal symmetry offers a new perspective for designing photocatalysts.

2D Ruthenium-Chromium Oxide with Rich Grain Boundaries Boosts Acidic Oxygen Evolution Reaction Kinetics

Ruthenium oxide is currently considered as the promising alternative to Ir-based catalysts employed for proton exchange membrane water electrolyzers but still faces the bottlenecks of limited durability and slow kinetics. Herein, a 2D amorphous/crystalline heterophase ac-Cr0.53Ru0.47O2-δ substitutional solid solution with pervasive grain boundaries (GBs) is developed to accelerate the kinetics of acidic oxygen evolution reaction (OER) and extend the long-term stability simultaneously. The ac-Cr0.53Ru0.47O2-δ shows a super stability with a slow degradation rate and a remarkable mass activity of 455 A gRu -1 at 1.6 V vs RHE, which is ≈3.6- and 5.9-fold higher than those of synthesized RuO2 and commercial RuO2, respectively. The strong interaction of Cr-O-Ru local units in synergy with the specific 2D structural characteristics of ac-Cr0.53Ru0.47O2-δ dominates its enhanced stability. Meanwhile, high-density GBs and the shortened Ru-O bonds tailored by amorphous/crystalline structure and Cr-O-Ru interaction regulate the adsorption and desorption rates of oxygen intermediates, thus accelerating the overall acidic OER kinetics.

Advancing BiVO4 Photoanode Activity for Ethylene Glycol Oxidation via Strategic pH Control

The photoelectrochemical (PEC) conversion of organic small molecules offers a dual benefit of synthesizing value-added chemicals and concurrently producing hydrogen (H2). Ethylene glycol, with its dual hydroxyl groups, stands out as a versatile organic substrate capable of yielding various C1 and C2 chemicals. In this study, we demonstrate that pH modulation markedly enhances the photocurrent of BiVO4 photoanodes, thus facilitating the efficient oxidation of ethylene glycol while simultaneously generating H2. Our findings reveal that in a pH = 1 ethylene glycol solution, the photocurrent density at 1.23 V vs. RHE can attain an impressive 7.1 mA cm-2, significantly surpassing the outputs in neutral and highly alkaline environments. The increase in photocurrent is attributed to the augmented adsorption of ethylene glycol on BiVO4 under acidic conditions, which in turn elevates the activity of the oxidation reaction, culminating in the maximal production of formic acid. This investigation sheds light on the pivotal role of electrolyte pH in the PEC oxidation process and underscores the potential of the PEC strategy for biomass valorization into value-added products alongside H2 fuel generation.

Enhancing the acidic oxygen evolution reaction performance of RuO2-TiO2by a reduction-oxidation process

As a promising alternative to Ir based acidic oxygen evolution reaction (OER) catalysts, Ru suffers from severe fading issues. Supporting it on robust oxides such as TiO2is a simple and effective way to enhance its lifetime. Here, we find that a simple reduction-oxidation process can further improve both activity and stability of RuO2-TiO2composites at high potentials. In this process, the degree of oxidation was carefully controlled to form Ru/RuO2heterostructure to improve OER activity. Moreover, due to the oxophilicity difference of Ru and Ti, the structure of catalysts was changed from supported to embedded, which enhanced the protective effect of TiO2and mitigated the dissolution of Ru element in acidic electrolyte, making as-prepared Ru/RuO2-TiO2with better durability at all tested potentials.

Spin-Steered Photosynthesis of H2O2 in Magnetic Single-Atom Modified Covalent Triazine Frameworks: A Density Functional Theory Study

Covalent Organic Frameworks (COFs) demonstrate promising potential in the photocatalytic synthesis of H2O2 owing to favorable light absorption, superior charge separation, and considerable surface area. However, the efficiency of H2O2 photosynthesis is impeded by insufficient O2 adsorption sites and a high reaction barrier. In this work, various metal single atoms (Fe, Co, Ni) are introduced onto covalent triazine frameworks (CTFs) with N-N coordination sites to significantly enhance O2 adsorption and optimize H2O2 synthesis. Computational findings suggest that the presence of Fe, Co, and Ni not only enhances O2 adsorption but also exerts an influence on the reaction pathway of H2O2. Significantly, Fe exhibits a distinct advantage in modulating O2 adsorption through its unique electron spin state when compared to Co and Ni, as confirmed by crystal orbital Hamilton population (COHP) analysis. Additionally, this integration of metal atoms also improves light absorption and charge separation in CTFs. The study provides strategic insight into elevating H2O2 production by incorporating tailored metal single atoms into COFs.

Nanoconfinement Enables Photoelectrochemical Selective Oxidation of Glycerol via the Microscale Fluid Effect

The glycerol oxidation reaction (GOR) run with photoelectrochemical cells (PECs) is one of the most promising ways to upgrade biomass because it is thermodynamically favorable, while irreversible overoxidation leads to unsatisfactory product selectivities. Herein, a tunable one-dimensional nanoconfined environment was introduced into the GOR process, which accelerated mass transfer of glycerol via the microscale fluid effect and changed the main oxidation product from formic acid (FA) to glyceraldehyde (GLD), which led to retention of the heavier multicarbon products. The rate of glycerol diffusion in the nanochannels increased by a factor of 4.92 with decreasing inner diameters. The main product from the PEC-selective oxidation of glycerol changed from the C1 product FA to the C3 product GLD with a great selectivity of 60.7%. This work provides a favorable approach for inhibiting further oxidation of multicarbon products and illustrates the importance of microenvironmental regulation in biomass oxidation.

Core-Shell CoS2@MoS2 with Hollow Heterostructure as an Efficient Electrocatalyst for Boosting Oxygen Evolution Reaction

It is imperative to develop an efficient catalyst to reduce the energy barrier of electrochemical water decomposition. In this study, a well-designed electrocatalyst featuring a core-shell structure was synthesized with cobalt sulfides as the core and molybdenum disulfide nanosheets as the shell. The core-shell structure can prevent the agglomeration of MoS2, expose more active sites, and facilitate electrolyte ion diffusion. A CoS2/MoS2 heterostructure is formed between CoS2 and MoS2 through the chemical interaction, and the surface chemistry is adjusted. Due to the morphological merits and the formation of the CoS2/MoS2 heterostructure, CoS2@MoS2 exhibits excellent electrocatalytic performance during the oxygen evolution reaction (OER) process in an alkaline electrolyte. To reach the current density of 10 mA cm-2, only 254 mV of overpotential is required for CoS2@MoS2, which is smaller than that of pristine CoS2 and MoS2. Meanwhile, the small Tafel slope (86.9 mV dec-1) and low charge transfer resistance (47 Ω) imply the fast dynamic mechanism of CoS2@MoS2. As further confirmed by cyclic voltammetry curves for 1000 cycles and the CA test for 10 h, CoS2@MoS2 shows exceptional catalytic stability. This work gives a guideline for constructing the core-shell heterostructure as an efficient catalyst for oxygen evolution reaction.