Ternary Porous Cobalt Phosphoselenide Nanosheets: An Efficient Electrocatalyst for Electrocatalytic and Photoelectrochemical Water Splitting

Identification of Suitable Mesh Size of Commercial Stainless-Steel for Electrochemical Oxygen Evolution Reaction

The study examines the oxygen evolution reaction (OER) electrocatalytic efficiency of various stainless-steel mesh (SSM) sizes in electrolytic cells. Stainless steel is chosen due to its widespread availability and stability, making it an economically viable option. The primary objective of this investigation is to determine the optimal stainless-steel mesh size among those currently widely available on the market. The classification of stainless-steel mesh sizes as SS304 is confirmed by the minimal compositional variations observed across all mesh sizes through electron dispersive X-ray (EDX) spectra and X-ray fluorescence (XRF) analyses. Remarkably, CV experiments carried out at different scan rates indicate that SSM 200 has the maximum specific electrochemical surface area (ECSA). As a result, SSM 200 demonstrates superior performance in terms of current density response and shows the lowest overpotential in the alkaline medium compared to other stainless-steel mesh sizes. Furthermore, the SSM 200 exhibits a low overpotential of 337 mV at a current density of 10 mA/cm2 and a Tafel slope of 62.2 mV/decade, surpassing the performance of several previously reported electrodes for the OER. Stability tests conducted under constant voltage further confirm the remarkable stability of SSM 200, making it an ideal anode for electrolytic cell applications. These findings emphasize the cost-effectiveness and high stability of SSM 200, presenting intriguing possibilities for future research and advancements in this field.

Co9S8 core-shell hollow spheres for enhanced oxygen evolution and methanol oxidation reactions by sulfur vacancy engineering

Cobalt sulfides, especially Co9S8, have been widely studied as a potential earth-abundant electrocatalyst for many electrochemical reactions, such as oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). However, the electrocatalytic performance of Co9S8 is not satisfactory because of its comparatively sluggish charge transport and reaction kinetics. Defect engineering and constructing hollow nanostructures are effective methods to improve their electrocatalytic performance, therefore, exploring an efficient route to obtain Co9S8 catalysts, simultaneously possessing sulfur vacancies and hollow nanostructure, is necessary. In this study, Co9S8-x core-shell hollow spheres with sulfur vacancies were prepared via a two-step solvothermal strategy, followed by thermal treatment under an H2/Ar atmosphere. The content of sulfur vacancies can be regulated by varying the temperature during the thermal treatment. The obtained Co9S8-x core-shell hollow spheres exhibited interesting sulfur vacancy defect-dependent activity, one of which showed outstanding electrocatalysis performance for OER with an overpotential (η) of 294 m V (at 10 mA cm-2) and MOR catalysis efficiency (164.9 mA cm-2 at 1.8 V vs. RHE) in an alkaline medium. This study provides a promising and feasible pathway for developing efficient trifunctional electrocatalysts for renewable energy technologies.

Delaminated MnPS3 with Multiple Layers Coupled with Si Featuring Ultrahigh Detectivity and Environmental Stability for UV Photodetection

Silicon (Si), the dominant semiconductor in microelectronics yet lacking optoelectronic functionalities in UV regions, has been researched extensively to make revolutionary changes. In this study, the inherent drawback of Si on optoelectronic functionalities in UV regions is potentially overcome through heterostructure coupling of delaminated p-type MnPS3, having bulk, multiple-layer, and few-layer features, with n-type Si. By artificially mimicking the architectures of shrubs with unique UV shading phenomena, the revolutionary multiple-layer MnPS3 structures with staggered stacking configurations trigger outstanding UV photosensing performances, displaying an average EQE value of 1.1 × 103%, average photoresponsivity of 3.1 × 102 A/W, average detectivity of 1.9 × 1014 cm Hz1/2W1-, and average on/off ratio of 1.8 × 103 under 365 nm light. To the best of our knowledge, this is the first attempt toward realizing gate-free MnPS3-based UV photodetectors, while all of the photodetection outcomes are better than those of more sophisticated field-effect transistor (FET) designs, which have remarkable impacts on the practicality and functionality of next-generation UV optoelectronics.

Intermediates Regulation via Electron-Deficient Cu Sites for Selective Nitrate-to-Ammonia Electroreduction

Ammonia (NH3 ), known as one of the fundamental raw materials for manufacturing commodities such as chemical fertilizers, dyes, ammunitions, pharmaceuticals, and textiles, exhibits a high hydrogen storage capacity of ≈17.75%. Electrochemical nitrate reduction (NO3 RR) to valuable ammonia at ambient conditions is a promising strategy to facilitate the artificial nitrogen cycle. Herein, copper-doped cobalt selenide nanosheets with selenium vacancies are reported as a robust and highly efficient electrocatalyst for the reduction of nitrate to ammonia, exhibiting a maximum Faradaic efficiency of ≈93.5% and an ammonia yield rate of 2360 µg h-1 cm-2 at -0.60 V versus reversible hydrogen electrode. The in situ spectroscopical and theoretical study demonstrates that the incorporation of Cu dopants and Se vacancies into cobalt selenide efficiently enhances the electron transfer from Cu to Co atoms via the bridging Se atoms, forming the electron-deficient structure at Cu sites to accelerate NO3 - dissociation and stabilize the *NO2 intermediates, eventually achieving selective catalysis in the entire NO3 RR process to produce ammonia efficiently.

Co doping promotes the alkaline overall seawater electrolysis performance over MnPSe3 nanosheets

Herein, two-dimensional cobalt-doped MnPSe3 nanosheets (CMPS) were constructed, which served as an outstanding bifunctional catalyst for alkaline seawater splitting, i.e., offering the current density of 10 mA cm-2 with applied overpotentials of 59 and 300 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The assembled two-electrode system of CMPS//CMPS also demonstrated excellent catalytic activity (10 mA cm-2, 1.59 V) and can remain stable for more than 100 h. Moreover, the theoretical calculations showed that CMPS features a suitable H* adsorption beneficial for the HER, as well as a lower free energy barrier favorable for the OER.

Photoelectrochemical cells with a pyridine-anchored organic dye photoanode for efficient H2 generation by water reduction

TiO₂ photoelectrodes modified with organic dyes with pyridine anchoring groups are prepared, which are used as photoanodes of dye-sensitized photoelectrochemical cells for efficient water reduction with high photocurrent density and stability in aqueous solutions. Vigorous H₂ generation with a production rate of around 250 μmol h^-1 is realized with a photoanode of an active area of 5 × 5 cm².

Rational Fabrication of Defect-Rich and Hierarchically Porous Fe-N-C Nanosheets as Highly Efficient Oxygen Reduction Electrocatalysts for Zinc-Air Battery

The rational design of morphology and structure for oxygen reduction reaction (ORR) catalysts still remains a critical challenge. Herein, we successfully construct defect-rich and hierarchically porous Fe-N-C nanosheets (Fe-N-CNSs), by taking advantage of metal-organic complexation and a mesoporous template. Benefiting from the advantages of high density of active sites, fast mass transfer channels, and sufficient reaction area, the optimal Fe-N-CNSs demonstrate satisfactory ORR activity with an excellent half-wave potential of up to 0.87 V, desirable durability, and robust methanol tolerance. Noteworthy, the Fe-N-CNSs based zinc-air battery shows significant performance with a peak power density of 128.20 mW cm^-2 and open circuit voltage of 1.53 V, which reveals that the Fe-N-CNSs catalysts present promising practical application prospects. Therefore, we believe that this research will provide guidance for the optimization of Fe-N-C materials.

Spatial Relation Controllable Di-Defects Synergy Boosts Electrocatalytic Hydrogen Evolution Reaction over VSe2 Nanoflakes in All pH Electrolytes

Defect engineering of transition metal dichalcogenides (TMDCs) is important for improving electrocatalytic hydrogen evolution reaction (HER) performance. Herein, a facile and scalable atomic-level di-defect strategy over thermodynamically stable VSe₂ nanoflakes, yielding attractive improvements in the electrocatalytic HER performance over a wide electrolyte pH range is reported. The di-defect configuration with controllable spatial relation between single-atom (SA) V defects and single Se vacancy defects effectively triggers the electrocatalytic HER activity of the inert VSe₂ basal plane. When employed as a cathode, this di-defects decorated VSe₂ electrocatalyst requires overpotentials of 67.2, 72.3, and 122.3 mV to reach a HER current density of 10 mA cm^-2 under acidic, alkaline, and neutral conditions, respectively, which are superior to most previously reported non-noble metal HER electrocatalysts. Theoretical calculations reveal that the reactive microenvironment consists of two adjacent SA Mo atoms with two surrounding symmetric Se vacancies, yielding optimal water dissociation and hydrogen desorption kinetics. This study provides a scalable strategy for improving the electrocatalytic activity of other TMDCs with inert atoms in the basal plane.

Nanosheets of In2S3/S-C3N4-Dots for Solar Water-Splitting in Saline Water

Hydrogen generation from splitting of water under the photoelectrochemical (PEC) pathway is considered as the most promising strategy for covering the upcoming fuel crisis by taking care of all environmental issues. In this context, In₂S₃ can be explored as it is a visible light-active semiconductor with an appropriate band alignment with the water redox potential. Herein, In₂S₃ nanosheets are developed by the chemical method. The nanosheets of In₂S₃ absorb high visible light due to the manifold inside scattering and reflection. The PEC activity of In₂S₃ is enhanced because of the increase in the light absorbance of the materials. In the present work, at 1.18 V versus RHE in 3.5 wt % NaCl, a maximum 2.07 mA/cm² photocurrent density can be achieved by In₂S₃ nanosheets. However, In₂S₃ suffers strongly due to photo-corrosion. To improve the efficacy of the In₂S₃ nanosheets in saline water, the charge-carrier transportation ability of In₂S₃ is aimed to increase by decorating S-C₃N₄-dots on In₂S₃. The heterostructure of type-II is developed by sensitization of S-C₃N₄-dots on In₂S₃. It increases both the transportation of charge carriers as well as separation. In the heterostructure, the transient decay time (τ) increases, which indicates a decrease in photogenerated charge-carrier recombination. S-C₃N₄-dots also act as an optical antenna and increase the range of visible light absorbance of In₂S₃. The heterostructure can generate ∼2.38-fold higher photocurrent density of 1.18 V versus RHE in 3.5 wt % NaCl. The photoconversion efficiency of the heterostructure is 0.88% at 0.95 V versus RHE. The nanosheets of In₂S₃ and In₂S₃/S-C₃N₄-dots are stable, and photocurrent density is measured up to 2700 s under continuous back-illumination conditions.

Heterometal doping on nickel selenide corrugations for solar-assisted electrocatalytic hydrogen evolution

Since nickel exhibits good binding energy and is inexpensive, it is widely applied as a hydrogen evolution reaction (HER) electrocatalyst. Among all Ni-based materials, nickel selenide (NiSe) shows a unique electronic structure as a semiconductor with good electrocatalytic activity. Herein, we prepare Co-doped NiSe (Ni_1-xCo_xSe) with a structure of uniform corrugations by one-step chemical vapor deposition. For comparison, Fe-doped NiSe (Ni_1-xFe_xSe) and NiSe are also prepared using the same method. In alkaline electrolyte, Ni_1-xCo_xSe shows great HER performance in terms of low overpotential (93 mV@10 mA cm^-2 and 140 mV@50 mA cm^-2) and long-term stability. Moreover, with the assistance of solar energy, the overpotential needed for Ni_1-xCo_xSe is reduced, making Ni_1-xCo_xSe better than most reported NiSe-based HER catalysts. On the other hand, the current density of Ni_1-xCo_xSe is 13 mA cm^-2@93 mV and 63 mA cm^-2@140 mV with illumination, which is 30% and 26% higher than that without solar illumination assistance, respectively. Therefore, we believe that inducing sunlight to electrocatalytic hydrogen evolution in water splitting could be a supplementary footprint toward the utilization of solar energy.

The High Electrocatalytic Performance of NiFeSe/CFP for Hydrogen Evolution Reaction Derived from a Prussian Blue Analogue

Non-noble-metal-based chalcogenides are promising candidates for hydrogen evolution reaction (HER) by harnessing the architectural design and the synergistic effect between the elements. Herein, a porous bimetallic selenide (NiFeSe) nanocube deposited on carbon fiber paper (NiFeSe/CFP) was synthesized through a facile selenization reaction based on Prussian blue analogues (PBAs) as precursors. The NiFeSe/CFP exhibited excellent HER activity with an overpotential of just 186 mV for a current density of 10 mA cm−2 in 1.0 M KOH at ambient temperature, similar to most of the state-of-the-art transition metal chalcogenides. The corresponding Tafel slope was calculated to be 52 mV dec−1, indicating fast discharge of the proton during the HER. Furthermore, the catalyst could endure long-term catalytic tests and showed remarkable durability. The enhanced electrocatalytic performance of NiFeSe/CFP is attributed to the unique 3D porous configuration inherited from the PBA templates, enhanced charge transfer occurring at the heterogeneous interface due to the synergistic effect between the bimetallic phases, and the high conductivity improved by the formation of amorphous carbon shells during the selenization. These findings prove that the combination of inexpensive metal–organic framework precursors and hybrid metallic compounds is a feasible way to realize the performance enhancement of non-noble-metal-based chalcogenides towards alkaline HER.

Transition Metal Non-Oxides as Electrocatalysts: Advantages and Challenges

The identification of hydrogen as green fuel in the near future has stirred global realization toward a sustainable outlook and thus boosted extensive research in the field of water electrolysis focusing on the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). A huge class of compounds consisting of transition metal-based nitrides, carbides, chalcogenides, phosphides, and borides, which can be collectively termed transition metal non-oxides (TMNOs), has emerged recently as an efficient class of electrocatalysts in terms of performance and longevity when compared to transition metal oxides (TMOs). Moreover, the superiority of TMNOs over TMOs to effectively catalyze not only OERs but also HERs and ORRs renders bifunctionality and even trifunctionality in some cases and therefore can replace conventional noble metal electrocatalysts. In this review, the crystal structure and phases of different classes of nanostructured TMNOs are extensively discussed, focusing on recent advances in design strategies by various regulatory synthetic routes, and hence diversified properties of TMNOs are identified to serve as next-generation bi/trifunctional electrocatalysts. The challenges and future perspectives of materials in the field of energy conversion and storage aiding toward a better hydrogen economy are also discussed in this review.

N, P, O co-doped carbon filling into carbon nitride microtubes to promote photocatalytic hydrogen production

Carbon nitride (CN) as the photocatalytic hydrogen production catalyst has attracted great attentions but suffering from a poor performance due to the unsatisfied energy band gap and the low separation efficiency of photogenerated carriers. Herein, we create a simple method to construct a novel CN-based photocatalyst, i.e., the N, P, O co-doped carbon filled CN microtube, which presents a narrow band gap, a high separation efficiency of photogenerated carriers, and a good stability. In this novel structure, the tubular morphology of CN ensures a narrow band gap, and the N, P, O co-doped carbon facilitates the transfer of photogenerated electrons. Coupling these two further reduces the energy band gap and improves the separation efficiency. For the photocatalytic hydrogen evolution under the visible light, the optimal sample presents an ultrahigh hydrogen evolution rate of 1149.71 μmol g^-1 h^-1 ranking at the top level, which is 112.60 times that of traditional bulk CN. In addition, it also has a high reusability and good stability after four cycle experiments. This study has provided a new viewpoint to design or develop the high-efficient photocatalysts for hydrogen production.

Interface engineering of MoS2@Fe(OH)3 nanoarray heterostucture: Electrodeposition of MoS2@Fe(OH)3 as N2 and H+ channels for artificial NH3 synthesis under mild conditions

The electrocatalytic reduction of nitrogen (N₂) to ammonia (NH₃) has broad prospects for green and sustainable NH₃ production. Due to the electrocatalytic nitrogen reduction reaction (eNRR) performance of transition metal compound may be restricted with low yield rate, we develop transition metal interface engineering to improve the eNRR performance. Although the edge of MoS₂ catalyst is active, the MoS₂(001) surface is inert for N₂ electroreduction. Through the hydrothermal and electrodeposition methods, Fe(OH)₃ as N₂ and H⁺ channels coated on MoS₂ nanosheets array (MoS₂@Fe(OH)₃/CC) is synthesized. Such catalyst exhibits excellent eNRR performance in 0.1 M Na₂SO₄ with high Faradaic efficiency (2.76%) and NH₃ yield rate (4.23 × 10^-10 mol s^-1 cm^-2) at - 0.45 V (vs. RHE). This work may provide a new electrocatalyst synthesis pathway for artificial N₂ fixation. Density functional theory calculations show that electrodeposition Fe(OH)₃ can accelerate eNRR process rate of MoS₂.

Shining Light on Anion-Mixed Nanocatalysts for Efficient Water Electrolysis: Fundamentals, Progress, and Perspectives

This review introduces recent advances of various anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, (oxy)hydroxides, and borides) for efficient water electrolysis applications in detail. The challenges and future perspectives are proposed and analyzed for the anion-mixed water dissociation catalysts, including polyanion-mixed and metal-free catalyst, progressive synthesis strategies, advanced in situ characterizations, and atomic level structure-activity relationship. Hydrogen with high energy density and zero carbon emission is widely acknowledged as the most promising candidate toward world's carbon neutrality and future sustainable eco-society. Water-splitting is a constructive technology for unpolluted and high-purity H₂ production, and a series of non-precious electrocatalysts have been developed over the past decade. To further improve the catalytic activities, metal doping is always adopted to modulate the 3d-electronic configuration and electron-donating/accepting (e-DA) properties, while for anion doping, the electronegativity variations among different non-metal elements would also bring some potential in the modulations of e-DA and metal valence for tuning the performances. In this review, we summarize the recent developments of the many different anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, oxyhydroxides, and borides/borates) for efficient water electrolysis applications. First, we have introduced the general information of water-splitting and the description of anion-mixed electrocatalysts and highlighted their complementary functions of mixed anions. Furthermore, some latest advances of anion-mixed compounds are also categorized for hydrogen and oxygen evolution electrocatalysis. The rationales behind their enhanced electrochemical performances are discussed. Last but not least, the challenges and future perspectives are briefly proposed for the anion-mixed water dissociation catalysts.

Defective Bimetallic Selenides for Selective CO2 Electroreduction to CO

CO₂ electroreduction (CO₂ RR) to CO is promising for the carbon cycle but still remains challenging. Au is regarded as the most selective catalyst for CO₂ RR, but its high cost significantly hinders its industrial application. Herein, the bimetallic CuInSe₂ is found to exhibit an Au-like catalytic feature: i) the interaction of Cu and In orbitals induces a moderate adsorption strength of CO₂ RR intermediates and favors the reaction pathway; and ii) the hydrogen evolution is energetically unfavorable on CuInSe₂ , as a surface reconstruction along with high energy change will occur after hydrogen adsorption. Furthermore, the Se vacancy is found to induce an electron redistribution, slightly tune the band structure, and optimize the CO₂ RR route of bimetallic selenide. Consequently, the Se-defective CuInSe₂ (V-CuInSe₂ ) achieves a highly selective CO production ability that is comparable to noble metals in aqueous electrolyte, and the V-CuInSe₂ cathode shows a satisfactory performance in an aqueous Zn-CO₂ cell. This work demonstrates that designing cost-effective catalysts with noble-metal-like properties is an ideal strategy for developing efficient electrocatalysts. Moreover, the class of transition bimetallic selenides has shown promising prospects as active and cost-effective electrocatalysts owing to their unique structural, electronic, and catalytic properties.

Advancing Photoelectrochemical Energy Conversion through Atomic Design of Catalysts

Powered by inexhaustible solar energy, photoelectrochemical (PEC) hydrogen/ammonia production and reduction of carbon dioxide to high added-value chemicals in eco-friendly and mild conditions provide a highly attractive solution to carbon neutrality. Recently, substantial advances have been achieved in PEC systems by improving light absorption and charge separation/transfer in PEC devices. However, less attention is given to the atomic design of photoelectrocatalysts to facilitate the final catalytic reactions occurring at photoelectrode surface, which largely limits the overall photo-to-energy conversion of PEC system. Fundamental catalytic mechanisms and recent progress in atomic design of PEC materials are comprehensively reviewed by engineering of defect, dopant, facet, strain, and single atom to enhance the activity and selectivity. Finally, the emerging challenges and research directions in design of PEC systems for future photo-to-energy conversions are proposed.

Highly Mesoporous Cobalt-Hybridized 2D Cu3P Nanosheet Arrays as Boosting Janus Electrocatalysts for Water Splitting

Recently, developing economical electrocatalysts with high performance in water decomposition has become a research hotspot. Herein, two kinds of cobalt-hybridized Cu₃P nanostructure array electrocatalysts (including highly mesoporous 2D nanosheets and sugar gourd-like 1D nanowires) were controllably grown on a nickel foam substrate through a simple hydrothermal method combined with a subsequent phosphating treatment method. An electrocatalytic test indicated that the as-prepared 2D nanosheet array exhibited excellent activity and stability toward hydrogen evolution reaction under alkaline conditions, which offered a low overpotential of 99 mV at 10 mA/cm² and a small Tafel slope of 70.4 mV/dec, whereas a competitive overpotential of 272 mV was required for oxygen evolution reaction. In addition, the 2D nanosheet array delivered a low cell voltage of 1.66 V at 10 mA/cm² in a symmetric two-electrode system, implying its huge potential in overall water decomposition. The electrocatalytic performance is superior to the as-prepared 1D nanowire array and most of the Cu₃P-related electrocatalysts previously reported. Experimental measurements and first-principles calculations show that the excellent performance of the 2D nanosheet array can be attributed to its unique 2D mesoporous structure and hybridization of cobalt, which not only provide a large electrochemically active surface and fast electrocatalytic reaction kinetics but also weaken the binding strength of electrocatalytic reaction intermediates. The present study provides a simple and controllable approach to synthesize Cu₃P-based bimetallic phosphide nanostructures, which can be used as boosting Janus electrocatalysts for water decomposition.

Manipulation on active electronic states of metastable phase β-NiMoO4 for large current density hydrogen evolution

Non-noble transition metal oxides are abundant in nature. However, they are widely regarded as catalytically inert for hydrogen evolution reaction (HER) due to their scarce active electronic states near the Fermi-level. How to largely improve the HER activity of these kinds of materials remains a great challenge. Herein, as a proof-of-concept, we design a non-solvent strategy to achieve phosphate substitution and the subsequent crystal phase stabilization of metastable β-NiMoO₄. Phosphate substitution is proved to be imperative for the stabilization and activation of β-NiMoO₄, which can efficiently generate the active electronic states and promote the intrinsic HER activity. As a result, phosphate substituted β-NiMoO₄ exhibits the optimal hydrogen adsorption free energy (−0.046 eV) and ultralow overpotential of −23 mV at 10 mA cm⁻² in 1 M KOH for HER. Especially, it maintains long-term stability for 200 h at the large current density of 1000 mA cm⁻² with an overpotential of only −210 mV. This work provides a route for activating transition metal oxides for HER by stabilizing the metastable phase with abundant active electronic states.

Non-noble transition metal oxides are common yet typically poor hydrogen evolution catalysts due to scarce active electronic states. This work provides a route for achieving hydrogen evolution at high current densities by stabilizing a metastable NiMoO₄ phase with abundant active electronic states.

Vertical-orbital band center as an activity descriptor for hydrogen evolution reaction on single-atom-anchored 2D catalysts

The d-band center descriptor based on the adsorption strength of adsorbate has been widely used in understanding and predicting the catalytic activity in various metal catalysts. However, its applicability is unsure for the single-atom-anchored two-dimensional (2D) catalysts. Here, taking the hydrogen (H) adsorption on the single-atom-anchored 2D basal plane as example, we examine the influence of orbitals interaction on the bond strength of hydrogen adsorption. We find that the adsorption of H is formed mainly via the hybridization between the 1s orbital of H and the vertical d_z2orbital of anchored atoms. The other four projected d orbitals (d_xy/d_x2-y2, d_xz/d_yz) have no contribution to the H chemical bond. There is an explicit linear relation between the d_z2-band center and the H bond strength. The d_z2-band center is proposed as an activity descriptor for hydrogen evolution reaction (HER). We demonstrate that the d_z2-band center is valid for the single-atom active sites on a single facet, such as the basal plane of 2D nanosheets. For the surface with multiple facets, such as the surface of three-dimensional (3D) polyhedral nanoparticles, the d-band center is more suitable.

CoPSe: A New Ternary Anode Material for Stable and High-Rate Sodium/Potassium-Ion Batteries

The exploration of ideal electrode materials overcoming the critical problems of large electrode volume changes and sluggish redox kinetics induced by large ionic radius of Na⁺ /K⁺ ions is highly desirable for sodium/potassium-ion batteries (SIBs/PIBs) toward large-scale applications. The present work demonstrates that single-phase ternary cobalt phosphoselenide (CoPSe) in the form of nanoparticles embedded in a layered metal-organic framework (MOF)-derived N-doped carbon matrix (CoPSe/NC) represents an ultrastable and high-rate anode material for SIBs/PIBs. The CoPSe/NC is fabricated by using the MOF as both a template and precursor, coupled with in situ synchronous phosphorization/selenization reactions. The CoPSe anode holds a set of intrinsic merits such as lower mechanical stress, enhanced reaction kinetics, as well as higher theoretical capacity and lower discharge voltage relative to its counterpart of CoSe₂ , and suppressed shuttle effect with higher intrinsic electrical conductivity relative to CoPS. The involved mechanisms are evidenced by substantial characterizations and density functional theory (DFT) calculations. Consequently, the CoPSe/NC anode shows an outstanding long-cycle stability and rate performance for SIBs and PIBs. Moreover, the CoPSe/NC-based Na-ion full cell can achieve a higher energy density of 274 Wh kg^-1 , surpassing that based on CoSe₂ /NC and most state-of-the-art Na-ion full cells based on P-, Se-, or S-containing binary/ternary anodes to date.

Efficient mineralization of sulfanilamide over oxygen vacancy-rich NiFe-LDH nanosheets array during electro-fenton process

Electrochemical degradation of toxic sulfanilamide with inexpensive approach is in urgent demand due to the harmful effects of sulfanilamide for both humans and aquatic environments. Here, we reported an efficient mineralization of sulfanilamide by using NiFe-layered double hydroxide (NiFe-LDH) nanosheets array with abundant oxygen vacancies that was in situ grown on exfoliated graphene (EG) by a simple hydrothermal treatment at different temperatures. The hydrothermal temperature was carefully analyzed for control synthesis of oxygen vacancy-rich NiFe-LDH/EG nanosheets array (NiFe-LDH/EG-OVr) for sulfanilamide degradation. Owing to the abundant oxygen vacancies, NiFe-LDH/EG-OVr rapidly generated hydrogen peroxide (H₂O₂) and hydroxyl radical (•OH) during electro-Fenton (EF) process_, which resulted in the 98% mineralization of sulfanilamide in first 80 min. The radicals trapping experiments revealed that the •OH radicals was participated as the main active oxidation species in the efficient mineralization of sulfanilamide. The present results indicated that the oxidative attack by •OH radicals initiated the degradation process of sulfanilamide. During the total degradation of sulfanilamide, several organic compounds including aminophenol, hydroquinone, and oxalic acid, were identified as main intermediates by using gas chromatography-mass spectroscopy (GC-MS) and high-performance liquid chromatography-mass spectroscopy (HPLC-MS).

Controlling the coordination environment of Co atoms derived from Co/ZIF-8 for boosting photocatalytic H2 evolution of CdS

Regulating the coordination environment of metal-N_x species by replacing N with low electronegativity atoms is an approach of tuning the electrocatalytic performance of metal-based sites. However, such effects on the enhancement of photocatalytic H₂ evolution over semiconductors are not discussed yet. Herein, we designed and prepared Co-based cocatalysts with controlled coordination environment via calcination Co/ZIF-8 loaded with triphenylphosphine followed by a sulfurization treatment. It was then used as cocatalyst to modify CdS. The effects of the coordination environment of Co atoms on the H₂ evolution activity of CdS were discussed. The obtained Co was co-stabilized by N, P, and S atoms and embedded in graphitic carbon (denoted as Co-N_xPS/C). Experimental results indicated that the Co-N_xPS/C exhibited high activity in enhancing H₂ evolution of CdS with a value of 1260 μmol after 5 h irradiation. The simultaneous replacement of N with P and S atoms in N-stabilized Co embedded in carbon could enhance light harvesting, accelerate the transfer of photogenerated electrons from CdS to carbon with increased electrons accumulation ability and conductivity, improve charge separation efficiency, and enhance proton reduction kinetics. It is believed that the results of this study could promote the development of other high performance MOF-derived atomically dispersed cocatalysts to increase photocatalytic H₂ evolution.

In situ identification of the electrocatalytic water oxidation behavior of a nickel-based metal-organic framework nanoarray

Metal-organic frameworks (MOFs) have been identified as one of the promising electrocatalysts for the oxygen evolution reaction (OER). However, direct observation of the electrocatalytic behavior of MOF-based electrocatalysts remains extremely challenging, which is of great significance to understand their electrocatalytic mechanism. Herein, we developed a vertically oriented Ni-based MOF nanosheet array doped with 2.09 wt% Ce (denoted as Ce-NiBDC/OG). Ce-NiBDC/OG displayed a low overpotential of 265 mV to deliver a 10 mA cm^-2 current density for the OER. In situ spectroscopy and operando microscopy visualized the phase transformation behavior of Ce-NiBDC/OG to Ce-doped NiOOH induced by electrochemical activation, which was regarded as the real active site. Mechanistic studies revealed that, for the Ce-NiBDC/OG-derived catalyst, the doping of Ce species in NiOOH significantly increased the adsorption of *OH, and further reduced the energy barriers of the rate-determining step (*OH→*O).

Atomic-Level and Modulated Interfaces of Photocatalyst Heterostructure Constructed by External Defect-Induced Strategy: A Critical Review

Despite the existence of numerous photocatalyst heterostructures, their separation efficiency and charge flow precision remain low due to the poor study on interfacial properties. The photocatalysts with confined defects can effectively control the photogenerated carrier migration, but the metastability of such defects considerably decreases the photocatalyst stability. Meanwhile, the introduction of defective region can increase the coordinative unsaturation and delocalize local electrons to promote their interactions with the molecules/ions in that region. The selective growth of modulated heterogeneous interface by defect-induced strategy may not only increase the stability of defective structures, but also enhance the migration of interfacial charges. Using this method, photocatalytic heterostructures with low contact resistances and intimate interfaces are constructed to achieve the optimal charge migration in terms of efficiency and accuracy. In this work, the point, linear, and planar heterogeneous interfaces and related defect engineering techniques are discussed. Particularly, it is focused on the external, defect-induced interfacial heterogeneities with various spatial and dimensional configurations, which exhibit modulated and controllable interfacial properties. Furthermore, the main aspects of fabricating photocatalyst heterostructures by the defect-induced strategy, including the i) controllable generation of defects, ii) advanced characterization methods, and iii) elaborate construction of the minimal interface, are described.

Synergism of 1D/2D boride/MXene nanosheet heterojunctions for boosted overall water splitting

Transition metal boride (TMB) as a new type of catalyst has attracted much attention in recent years.

Active Site Engineering in Porous Electrocatalysts

Electrocatalysis is at the center of many sustainable energy conversion technologies that are being developed to reduce the dependence on fossil fuels. The past decade has witnessed significant progresses in the exploitation of advanced electrocatalysts for diverse electrochemical reactions involved in electrolyzers and fuel cells, such as the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), the CO₂ reduction reaction (CO₂ RR), the nitrogen reduction reaction (NRR), and the oxygen evolution reaction (OER). Herein, the recent research advances made in porous electrocatalysts for these five important reactions are reviewed. In the discussions, an attempt is made to highlight the advantages of porous electrocatalysts in multiobjective optimization of surface active sites including not only their density and accessibility but also their intrinsic activity. First, the current knowledge about electrocatalytic active sites is briefly summarized. Then, the electrocatalytic mechanisms of the five above-mentioned reactions (HER, ORR, CO₂ RR, NRR, and OER), the current challenges faced by these reactions, and the recent efforts to meet these challenges using porous electrocatalysts are examined. Finally, the future research directions on porous electrocatalysts including synthetic strategies leading to these materials, insights into their active sites, and the standardized tests and the performance requirements involved are discussed.

Cobalt-based heterogeneous catalysts in an electrolyzer system for sustainable energy storage

Nowadays, the production of hydrogen and oxygen focuses on renewable energy techniques and sustainable energy storage. A substantial challenge is to extend low-cost electrocatalysts consisting of earth-abundant resources, prepared by straightforward approaches that display high intrinsic activity compared to noble metals. The expansion of bifunctional catalysts in alkaline electrolytes for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) has become very crucial in recent times. Herein, the recent progress in cobalt-based HER-OER electrocatalysts has been are brushed up and numerous bifunctional cobalt-based catalysts such as cobalt-oxides, phosphides, sulfides, selenides, nitrides, borides, carbides, perovskites, and MOF-based cobalt analogs have been investigated in detail. Specifically, much more attention has been paid to their structural variation, bifunctional activity, overpotential of the overall system, and stability. Cobalt-based catalysts with lower cell voltage, remarkable durability, and unique electronic structures, offer a new perspective in energy-related fields. In recent years, cobalt-based analogs with diagnostic facilities have been introduced due to their electronic structures, tunable d band structures, and tailorable active sites. This perspective also elucidates the present issues, promising ideas, and future forecasts for cobalt-based catalysts. The critical aspects of cobalt-based catalysts and the numerous opportunities, as discussed at the end, can possibly enrich the sustainable energy field.

A Universal Process: Self-Templated and Orientated Fabrication of XMoO4 (X: Ni, Co, or Fe) Nanosheets on MoO2 Nanoplates as Electrocatalysts for Efficient Water Splitting

Fabrication of superior nonprecious electrocatalysts is essential for water electrolysis. Herein, the epitaxial growth of the XMoO₄ (X = Ni, Co, Fe) nanosheets on the hexagonal MoO₂ nanoplates are carried out. The preoxidation of MoO₂ nanoplate is fatal to the epitaxial growth of a nanosheets array on MoO₂ nanoplates. The hierarchical heterostructure of the vertically aligned NiMo nanosheets on MoO₂ nanoplate (NiMo/MoO₂) is well-maintained in the process of in situ topotactic reduction transformation from NiMoO₄·xH₂O/MoO₂. Attributing it to the rich electroactive sites from nanosheets array, together with the intrinsic electrocatalytic performance of NiMo alloy, the as-engineered NiMo/MoO₂ as electrocatalyst exhibits admirable hydrogen evolution reaction (HER) activity with a small onset potential of -12 mV vs RHE (1 mA cm^-2) and a tafel value of 43.6 mV dec^-1 at alkaline media. Furthermore, the obtained CoMoO₄/MoO₂ possesses excellent oxygen evolution performance, which is verified by an ultralow overpotential of 230 mV@10 mA cm^-2, small Tafel slope (51 mV dec^-1), and robust durability. The developed NiMo/MoO₂ and CoMoO₄/MoO₂ electrocatalysts are assembled into an alkaline electrolyzer, which affords a cell potential of 1.51 V at 10 mA cm^-2, as well as outstanding operational durability, which is superior to the typically constructed 20 wt % Pt/C-RuO₂ system (1.59 V at 10 mA cm^-2). Hence, the universal strategy using MoO₂ nanoplates as Mo source and epitaxial substrate may be extended to explore and construct economical and superior Mo-based electrocatalysts for water electrolysis.

CoNiFe Layered Double Hydroxide/RuO2.1 Nanosheet Superlattice as Carbon-Free Electrocatalysts for Water Splitting and Li-O2 Batteries

Efficient electrocatalysts are highly demanded for oxygen evolution reaction (OER) in water splitting and metal-air batteries. Here, superlattice structured materials composed of CoNiFe layered double hydroxide (LDH)/ruthenium oxide nanosheets are synthesized as carbon-free electrocatalysts for OER. The positively charged CoNiFe LDH and negatively charged RuO_2.1 are alternately stacked at the molecular level into superlattice-like hybrids by electrostatic interaction upon mixing their dispersions under suitable conditions. Such heterostructured composites are found to act as effective catalysts toward OER of water splitting with a small overpotential of 281 mV and Tafel plot of 48.9 mV/decade. Such composites also serve as efficient carbon-free cathode catalysts for aprotic Li-O₂ batteries with remarkable higher specific capacities and lower overvoltages than RuO₂ nanoparticles. The superior performance may be attributed to the peculiar superlattice structure, resulting in strong interfacial electronic coupling, better electrical conductivity, and the suppression of side reactions caused by traditional carbon-based materials. Furthermore, potential difference between RuO_2.1 and CoNiFe LDH nanosheets is observed directly by scanning Kelvin probe microscopy, indicating that electrostatic fields might be induced in the superlattice structures to benefit the transport of electrons and charged ions as well as the catalytic process.

Fe, Al-co-doped NiSe2 nanoparticles on reduced graphene oxide as an efficient bifunctional electrocatalyst for overall water splitting

Developing low-cost and highly efficient electrocatalysts for overall water splitting is of far-reaching significance for new energy conversion. Herein, dual-cation Fe, Al-co-doped NiSe2 nanoparticles on reduced graphene oxide (Fe, Al-NiSe2/rGO) were prepared as a bifunctional electrocatalyst for overall water splitting. The dual-cation doping can induce a stronger electronic interaction between the foreign atoms and host catalyst, for optimizing the adsorption energy of reaction intermediates. Meanwhile, the leaching out of Al from the crystal structure of the target product during the alkaline wash creates more defects and increases the active site exposure. As a result, the Fe, Al-NiSe2/rGO catalyst exhibits excellent catalytic activities for both the OER and HER with an overpotential of 272 mV @η10 for the OER in 1.0 M KOH and 197 mV @η10 for the HER in 0.5 M H2SO4, respectively. A two-electrode electrolyzer using Fe, Al-NiSe2/rGO as the anode and cathode shows a low voltage of 1.70 V at the current density of 10 mA cm-2. This study emphasizes the synergistic contribution of the dual-cation co-doping effect and more defects created by Al leaching to boost the performance of water splitting.

A Superaerophobic Bimetallic Selenides Heterostructure for Efficient Industrial-Level Oxygen Evolution at Ultra-High Current Densities

Cost-effective and stable electrocatalysts with ultra-high current densities for electrochemical oxygen evolution reaction (OER) are critical to the energy crisis and environmental pollution. Herein, we report a superaerophobic three dimensional (3D) heterostructured nanowrinkles of bimetallic selenides consisting of crystalline NiSe2 and NiFe2Se4 grown on NiFe alloy (NiSe2/NiFe2Se4@NiFe) prepared by a thermal selenization procedure. In this unique 3D heterostructure, numerous nanowrinkles of NiSe2/NiFe2Se4 hybrid with a thickness of ~ 100 nm are grown on NiFe alloy in a uniform manner. Profiting by the large active surface area and high electronic conductivity, the superaerophobic NiSe2/NiFe2Se4@NiFe heterostructure exhibits excellent electrocatalytic activity and durability towards OER in alkaline media, outputting the low potentials of 1.53 and 1.54 V to achieve ultra-high current densities of 500 and 1000 mA cm-2, respectively, which is among the most active Ni/Fe-based selenides, and even superior to the benchmark Ir/C catalyst. The in-situ derived FeOOH and NiOOH species from NiSe2/NiFe2Se4@NiFe are deemed to be efficient active sites for OER.

Phthalocyanine-sensitized evolution of hydrogen and degradation of organic pollutants using polyoxometalate photocatalysts

In this study, 2 (3), 9 (10), 16 (17), 23 (24)-tetrakis-(8-quinoline-oxy) phthalocyanine zinc(II) (ZnQPc) was prepared and then quaternized to obtain water soluble zinc phthalocyanine (ZnQPc⁴⁺). Then, ZnQPc⁴⁺ was used as a photosensitizer for a series of POM catalysts, including Dawson type K₆[α-P₂W₁₈O₆₂]·14H₂O (P₂W₁₈) and K₁₀[α-P₂W₁₇O₆₁]·20H₂O (P₂W₁₇) and Keggine type H₃PW₁₂O₄₀·xH₂O (PW₁₂). The Keggin type PW₁₂ showed higher efficiency with 18.2 μmol of H₂ evolution (turnover number (TON) = 14,550) for 6 h upon ZnQPc⁴⁺ sensitization in relation to two Dawson P₂W₁₇ and P₂W₁₈ in a visible light-driven water-soluble system with isopropanol and H₂PtCl₆·6H₂O. In addition, the complexes of ZnQPc⁴⁺ with a series of POM catalysts (P₂W₁₇, P₂W₁₈, and PW₁₂) were also used as photocatalysts for the degradation of methylene blue (MB) in water, and it was found that the complexes of ZnQPc⁴⁺ with P₂W₁₇ and PW₁₂ showed improved photocatalytic activity, and the degradation rates of MB reached 100% at a small dosage under natural pH and visible light. The high efficacy of POM catalysts for H₂ evolution and the degradation of MB were attributed to the sensitization of POMs by ZnQPc⁴⁺, which was enabled by the transfer of photogenerated electrons of ZnQPc⁴⁺ to the lowest unoccupied molecular orbital (LUMO) of POM.

A high-activity bimetallic OER cocatalyst for efficient photoelectrochemical water splitting of BiVO4

BiVO4 has been widely used as a photoanode material, while the slow surface oxygen evolution reaction (OER) kinetics still severely hinders its performance. Here, an efficient bimetallic cocatalyst (named FeSnOS) was obtained by post-annealing a Fe/Sn-containing metal chalcogenide coordination compound to enhance the OER activity of BiVO4. The synergistic effect of Fe and Sn species in the amorphous FeSnOS cocatalyst efficiently lowers the interface impedance of the photoanode, reduces the electrochemical reaction overpotential, and promotes the surface OER dynamics. At the same time, a type-II heterojunction was constructed due to the process of post-annealing, which efficiently improves the bulk phase charge separation efficiency of the photoanode. The obtained optimal photoanode (named FeSnOS-BiVO4) shows a photocurrent density of 3.1 mA cm-2 at 1.23 V vs. the reversible hydrogen electrode, which is 3.4 times higher than that of the pristine BiVO4 photoanode, and its onset potential shifts negatively from 0.44 V to 0.25 V. This work presents a simple and effective method to build a bimetallic cocatalyst for improved photoelectrochemical performance, which extends the application of polymetallic metal chalcogenide complexes.

Fe doped Ni5P4 nanosheet arrays with rich P vacancies via phase transformation for efficient overall water splitting

Proper vacancy engineering is considered as a promising strategy to improve intrinsic activity, but it is challenging to construct rich vacancies by a simple strategy. Herein, Fe doped Ni₅P₄ nanosheet arrays with rich P vacancies are developed via a facile phase transformation strategy. Based on systematic investigations, we have demonstrated that an optimized surface electronic structure, abundant active sites and improved charge transport capability can be effectively achieved by vacancy engineering. Consequently, Fe doped Ni₅P₄ with rich vacancies show remarkable catalytic performances with 94.5 mV for the hydrogen evolution reaction (HER) and 217.3 mV for the oxygen evolution reaction (OER) at 10 mA cm^-2, respectively, as well as good durability. When directly employed as working electrodes, the as-obtained Fe doped Ni₅P₄ with rich vacancies can attain 10 mA cm^-2 at a low voltage of 1.59 V. This work demonstrates a feasible strategy for rationally fabricating electrocatalysts with rich vacancies via a simple phase transformation.