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Urea electrolysis can be used to treat wastewater containing urea and alleviate the energy crisis, so it is one of the best ways to solve environmental and energy problems. This paper reports the synthesis of M doped NiVS (M = Co, Ce and Cr) composites by a simple hydrothermal process for the first time. What is noteworthy is that the Ce-NiVS material as a catalytic electrode requires only 141 mV overpotential for the hydrogen evolution reaction (HER) and 1.291 V potential for the urea oxidation reaction (UOR) at a current density of 10 mA cm−2 in 1.0 M KOH and 0.5 M urea mixed alkaline solution. Using Ce-NiVS/NF as both the anode and cathode for urea electrolysis, a current density of 10 mA cm−2 is driven by a voltage of only 1.55 V, which is better than most previous catalysts. Experimental results demonstrate that the excellent catalytic activity of Ce-NiVS materials is due to the formation of a large number of active sites and the improvement of conductivity due to doping with Ce. Density functional theory calculation shows that the VS4 material has a small Gibbs free energy of hydrogen adsorption, which plays a major role in the hydrogen production process, and Ce-NiS has a higher density of states (DOS) near the Fermi level, indicating that Ce-NiS has better electronic conductivity. The synergistic catalysis of VS4 and Ce-NiS promoted the hydrogen production performance of the Ce-NiVS material. This work provides guidance for the optimization and design of low-cost electrocatalysts to replace expensive precious metal-based electrocatalysts for overall urea electrolysis. [ABSTRACT FROM AUTHOR]

Cocatalysts are usually applied in the photocatalytic water splitting process to accelerate the kinetics of the hydrogen evolution reaction (HER). Specifically, the transition metal nitride (Mo2N) featuring a unique local surface plasmon resonance (LSPR) effect has exhibited great potential to function as a HER cocatalyst. However, the low metallicity of Mo2N hampers its ability to improve charge separation. To address this issue, transition metal atom doping (Co and Cu) engineering was used to modulate the electronic structure of Mo2N nanosheets to achieve a higher electrical conductivity and a lower hydrogen adsorption free energy (‖ΔGH*‖), thereby favoring the HER kinetics. Density functional theory (DFT) calculations and experimental results showed that Co-doping and Cu-doping mainly take place at Mo sites in the crystal structure of Mo2N to form stable structures of Co doped Mo2N (Co–Mo2N) and Cu doped Mo2N (Cu–Mo2N). Compared with pristine Mo2N, both Cu–Mo2N and Co–Mo2N demonstrated a much improved cocatalytic effect over g-C3N4 in promoting charge separation, accelerating HER kinetics and enhancing light absorption. The Co–Mo2N with the highest conductivity and lowest ‖ΔGH*‖ illustrated the best cocatalytic effect, and the H2 production performance (367.8 μmol g−1 h−1) of Co–Mo2N/g-C3N4 achieved was 10 and 5 times higher than those of Mo2N/g-C3N4 and Cu–Mo2N/g-C3N4. This paper provides significant guidance in the design and development of efficient cocatalysts for the HER application. [ABSTRACT FROM AUTHOR]

MoSe2 as one graphene-like 2D transition metal selenide has attracted great attention. However, its application for the hydrogen evolution reaction (HER) is still restricted by the poor electrical conductivity and structural restacking. In this work, an excellent electrocatalyst for hydrogen production is developed based on the in situ synthesis of V-doped MoSe2 confined on carbon black nanoparticles (denoted as V-MoSe2/CB) via a sol–gel process. The characterization results show that the carbon black nanoparticles can protect the V-MoSe2 nanosheets from agglomeration, resulting in ultra-thin thickness and short vertical lattice arrays. Meanwhile, density functional theory (DFT) calculations indicate that vanadium doping can optimize the electronic structure of MoSe2. Accordingly, compared to the pure MoSe2, V-MoSe2 and MoSe2/CB electrocatalysts, V-MoSe2/CB exhibits improved electrocatalytic activity with a small overpotential of 166 mV at −10 mA cm−2 and a small Tafel slope of 65 mV dec−1. This work paves a new way for improving the HER performance through synergistic morphology, structure and electronic regulation. [ABSTRACT FROM AUTHOR]

Porphyrins have been widely used in designing photocatalyst systems. However, finding an effective strategy to improve the intrinsic photocatalytic activity of porphyrin molecules remains a challenge. Here, two new porphyrins, meso-tetra(5-carboxyfuryl)porphyrin (H2TCFP) and meso-tetra(5-carboxythienyl)porphyrin (H2TCTP), were successfully synthesized and compared with meso-tetra(m-carboxyphenyl)porphyrin (H2TmCPP), to clarify the influence of the organic unit bridging the carboxyl acid group with the porphine ring on the photocatalytic activity of porphyrin for H2 evolution from water splitting. The H2 evolution rates of 10.8 mmol g−1 h−1 observed for H2TCFP and 9.7 mmol g−1 h−1 for H2TCTP are both larger than 8.0 mmol g−1 h−1 observed for H2TmCTP under optimal conditions. The best photocatalytic activity observed for H2TCFP was investigated through experiments and density functional theory (DFT) calculations and was interpreted in terms of the combined effect of several key factors of the entire photocatalytic process, including the high absorptivity of UV light, high separation efficiency of photogenerated carriers, and low Gibbs energy required for associated water splitting. Meanwhile, the concentration-dependent performance of photocatalytic activity was analyzed and attributed to the aggregation and light-bleaching effect exerted on porphyrins. [ABSTRACT FROM AUTHOR]

The design of low-cost and high-performance bifunctional catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of great significance for overall water splitting. Herein, RuNi single atom alloy (SAA) decorated on reduced graphene oxide (RuNi@rGO) was synthesized by a facile strategy for use as a bifunctional HER/OER catalyst. The as-obtained RuNi@rGO catalyst exhibits outstanding electrocatalytic activities with an ultralow overpotential for the HER (15 mV) and the OER (240 mV) at a current density of 10 mA cm−2. Density functional theory (DFT) calculations demonstrate that the introduction of Ru single atoms can evidently change the electron distribution and coordination environment around Ni, and reduce the intermediate's adsorption free energy of RuNi@rGO, thus facilitating the HER/OER catalytic rate. Moreover, when used as the cathode and anode of a two-electrode system, the RuNi@rGO-based water splitting device exhibits a low potential of 1.52 V at a current density of 10 mA cm−2, as well as a high faradaic efficiency almost up to 100%, making RuNi@rGO bifunctional electrocatalysts attractive for energy storage and conversion. [ABSTRACT FROM AUTHOR]

The electrocatalytic CO2 reduction reaction (CO2RR) offers a fascinating approach to converting CO2 into valuable chemical feedstocks. Up to now, the development of highly efficient electrocatalysts has been a significant bottleneck in this field. In this study, employing density functional theory (DFT) calculations, we design a range of stable two-dimensional (2D) metalloporphyrin organic frameworks (TM-PMOFs, TM = Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, and Ag, respectively) built by copper clusters and metalloporphyrin (TM-TCPP), whose CO2RR performance is studied in detail. Among them, the 2D cobaltporphyrin-based organic framework (Co-PMOF) is identified to be the best CO2RR electrocatalyst on account of its low limiting potential (−0.53 V), whose enhanced electrocatalytic performance can be attributed to the presence of numerous active sites on both sides of its 2D framework, as well as the synergistic effect between copper clusters and cobaltporphyrins in facilitating CO2 reduction. These findings provide valuable insights and encourage further experimental research on metallic 2D PMOF materials for CO2 electrochemical reduction. [ABSTRACT FROM AUTHOR]

The electronic state of metallic centers plays a crucial role in electrocatalytic reactions such as oxygen evolution reaction (OER), which usually require high-valence transition metallic centers. Herein, we propose an organic ligand coordination strategy to modulate the electronic state of metallic centers in NiFe LDH, by introducing three different organic linkers including 2,6-naphthaleneducarboxylic acid, 4,4′-bipyridine, and 1H-1,2,3-triazole on the surface of NiFe LDH to derive atomic-layered metal–organic framework (NiFe LDH@MOF). Experimental results indicate that the electronic structure of metal centers in the composite was modified after the coordination of organic linker, among which the most amount of high-valence state was for Fe species in the 1H-1,2,3-triazole involved catalysts (NiFe LDH@MOF-3). Density functional theory (DFT) calculations further demonstrate that the 1H-1,2,3-triazole linkers around Fe centers optimized the d-band center together with the beneficial Gibbs free energy of the intermediate. Therefore, NiFe LDH@MOF-3 exhibited a superior electrocatalytic OER performance with a low overpotential of 242 mV to achieve a current density of 100 mA cm−2, a small Tafel slope of 32.3 mV dec−1. This work provides a general strategy for the modulation of the electronic structure of metallic centers using organic linker coordination to achieve a high-performance electrocatalyst. [ABSTRACT FROM AUTHOR]

The construction of highly active and stable transition phosphide-based materials is widely regarded as an alternative approach to the use of Pt-based catalysts in the field of electrocatalytic hydrogen evolution. Herein, self-supported heterostructure Co–Ni phosphides (denoted as CoxNi1−x-P) were synthesized with different metal ratios by a low temperature electrodeposition strategy. Impressively, the optimized heterogeneous Co0.5Ni0.5-P nanocomposites displayed outstanding hydrogen evolution performance, with low overpotentials of 67 mV and 181 mV to deliver current densities of 10 mA cm−2 and 100 mA cm−2 in alkaline electrolyte. X-ray photoelectron spectroscopy revealed the optimized electronic structure of Co0.5Ni0.5-P, which led to an improvement in the conductivity. Density functional theory calculations demonstrated that the Co0.5Ni0.5-P heterostructure could provide a more optimal water-dissociation-related Volmer process for hydrogen evolution reaction (HER), in which water molecules could be easily activated on Co0.5Ni0.5-P with a low energy barrier. Moreover, the downshift of the d-band center confirmed the optimized H adsorption, further accelerating the HER kinetics. [ABSTRACT FROM AUTHOR]

Black phosphorene (BP) is a metal-free two-dimensional photocatalyst with potential for visible-light-driven photocatalytic H2 evolution. However, its inert basal plane toward the HER hinders its practical application. To overcome this problem, we design a novel nonprecious metal–nonmetal co-doping method of BP to activate its inert basal plane and improve photocatalytic HER performance. Through density functional theory (DFT) calculations, we systematically investigate the photocatalytic performance of nonprecious metal and nonmetal co-doped BPs. Our results show that V–N co-doped BP exhibits excellent thermodynamic stability, suitable band structure, improved carrier separation, superior adsorption and dissociation energies and enhanced visible-light absorption coefficient. Importantly, V–N co-doping successfully activates the inert basal plane of BP, allowing it to drive the HER under illumination (ΔGH = −0.12 eV). This study highlights the potential of nonprecious metal–nonmetal co-doping to enhance the photocatalytic activity of BP, providing invaluable insights for advancing the field of co-doped BP in photocatalysis. [ABSTRACT FROM AUTHOR]

Sulfide compounds offer promising alternatives for electrocatalysts in water splitting, thanks to their diverse nature, intrinsic activities, affordability, and abundance in the Earth's crust. However, the limited active sites, hindered substance transport, larger particle size, and structural collapse restrict their performance in the electrolysis of water. In order to achieve a dual-functional catalyst with multiple catalytic sites, it is often necessary to construct heterogeneous or composite structures. However, this typically leads to an increase in catalyst resistance and also affects its operational stability. In response, we successfully prepared a high-entropy sulfide (ZnCoMnFeAlMg)9S8 through a low-temperature solvothermal method. This approach resulted in a reduction in grain size and a doubling of the specific surface area. The high entropy not only maintains the stability of the structure but also induces electron interactions within the catalyst through the interactions of multiple metals. This exposure of more active sites enables the realization of a dual-functional catalyst with multiple catalytic sites within a single structure. In addition, the increased presence of high-valence Fe and Ni ions promotes the chemisorption of intermediates, facilitating electron transfer during the reaction process. Benefiting from this multi-scale regulation strategy, the (ZnCoMnFeAlMg)9S8 displays an ultralow overpotential of 1.39 V at 10 mA cm−2 and a small Tafel slope of 35.3 mV dec−1. Density functional theory calculations indicate that high entropy can significantly modulate the local charge distribution and electronic properties of sulfides, thereby achieving optimal adsorption energy and reducing the potential energy barrier for hydrolysis. This study introduces a fresh approach to the functionalization of high entropy nanomaterials, while simultaneously enhancing the performance of water splitting catalysts. [ABSTRACT FROM AUTHOR]

In this study, two new heteroleptic complexes with compositions [Ni(mtsq)1.85Cl0.15(dppe)](CH2Cl2)0.06(CH3OH)0.09 (Ni-mtsq) and [Cu(mtsq)(PPh3)2] (Cu-mtsq) (dppe = 1,2-bis-(diphenylphosphino)ethane; PPh3 = triphenylphosphane and mtsq = 3-ethoxycyclobutenedione-4-thiolate) have been synthesized and characterized by spectroscopy analyses as well as by single crystal X-ray diffraction technique. X-ray analyses reveal square planar geometry around Ni(II) in Ni-mtsq, where Ni(II) coordinates with two sulfur centres of two mtsq ligands with monodentate coordination and two phosphorus centres of the dppe ligand in chelating mode. Unlike Ni-mtsq, Cu(I) in Cu-mtsq adopts a tetrahedral geometry, which is satisfied by sulfur and oxygen centres of one mtsq ligand with a bidentate coordination mode and two phosphorus centres of two PPh3 ligands. The supramolecular architecture of both Ni-mtsq and Cu-mtsq is sustained by intermolecular C–H⋯π and O⋯H interactions. Also, Ni-mtsq exhibits intriguing intramolecular semicoordination Ni⋯O and π⋯π non-covalent interactions. The nature of these interactions has been addressed with the aid of Hirshfeld surface analysis, density functional theory and quantum theory of atoms in molecules (QTAIM) analyses and has been visualized with the help of non-covalent interactions reduced density gradient (NCI-RDG). Further, the emissive nature of Cu-mtsq in a solution and solid phase suggests aggregation-induced emission with a bathochromic shift in the solid phase as compared to the solution phase. Both complexes have been used as electrocatalysts for oxygen and hydrogen evolution reactions, which suggests that Cu-mtsq offers better catalysis due to the presence of a redox active, less hindered Cu(I) centre with an η10 of 600 mV and a Tafel slope of 228 mV dec−1 in the OER, while in HER too, Cu-mtsq exhibited the best onset potential of −0.36 V with an η10 of 647 mV. Also, homogeneous electrocatalysis for the HER for both complexes was investigated using trifluoroacetic acid as the hydrogen source, which suggests a better electrocatalytic performance of Cu-mtsq. [ABSTRACT FROM AUTHOR]

A novel dinuclear copper complex, [CuII2(L1)2] (L1 = 2-{[2-(8-hydroxyquinolin-2-yl)-1H-benzimidazol-1-yl]methyl}quinolin-8-ol) was synthesised and characterised through various spectroscopic techniques. This dinuclear complex (as an electrocatalyst) was employed to examine the catalytic ability towards an electrochemical hydrogen evolution reaction (HER). Redox studies in 95/5 (v/v) DMF/H2O with the addition of 30-equivalent AcOH (acid source) led to higher catalytic activities for the HER. The evolved H2, as the resultant product, was detected and confirmed from gas chromatography to afford a faradaic efficiency of 93% at an applied potential of −1.9 V vs. SCE. Based upon measurements of open-circuit potential and electrocatalytic responses, the mechanistic route for the reduction process using [CuII2(L1)2] was elucidated. Density functional theory studies reveal that through a concerted proton-coupled electron transfer (PCET) path, the HER proceeded via the formation of a Cu–H bond with a low activation energy for the dehydrogenation reaction. [ABSTRACT FROM AUTHOR]

Covalent triazine frameworks (CTFs) involving donor-π bridge-acceptor (D–π–A) motifs with the electron-withdrawing triazine unit as the acceptor have been regarded as one of the most promising materials for photocatalytic water splitting. The intrinsic features of π-bridges play a critical role in tailoring the polymer properties as well as the photocatalytic performance. Introducing suitable conjugated units as the π-bridge is expected to effectively tune the electronic structure of the resultant D–π–A CTFs and facilitate photo-generated charge separation. However, systematic studies on how different π-bridges would influence the photoelectronic properties of D–π–A type CTFs are still limited. Herein, three types of CTFs with well-defined D–π–A structures named Ben-CTF, BenT-CTF and BenP-CTF were synthesized to investigate the effects of different π-bridges (benzene, thiophene and pyridine units) on the performance of photocatalytic water splitting for hydrogen production. Comprehensive experiments and density functional theory (DFT) calculations revealed that BenP-CTF with the pyridine unit as the π-bridge exhibited superior charge migration ability and higher photocatalytic hydrogen evolution reaction (HER) rates compared to the other CTFs. This work may provide a reference for the rational design and controllable synthesis of CTF materials for efficient photocatalysis. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospects and electrochemical performance of hydrogen evolution catalysts, extensive research on transition metal materials has been carried out. Among the many catalytic materials, cobalt is an element with potential for the hydrogen evolution reaction (HER) due to its abundant reserves, low cost, and small energy barrier for H adsorption. This review classifies the latest research on cobalt-based catalysts according to the types of compound, including cobalt-based sulfides, phosphides, carbides, borides, oxides, etc., and summarizes the latest research progress of cobalt-based compound catalysts in acidic and alkaline media. Strategies to tune the properties of cobalt-based compound catalysts for high catalytic activity for HER are focused on, including structural engineering, defect engineering, and doping, etc. The advantages and limitations of each modified approach are reviewed. Not only that, but also the catalytic activity and advantages of the catalyst are evaluated by using density functional theory (DFT) calculation-related descriptors, activity evaluation parameters, etc. Finally, limitations and challenges of cobalt-based materials for HER are presented, as well as prospects for future research. This paper aims to understand the chemical and physical factors that affect cobalt-based catalysts, and to find directions for future research on cobalt-based catalysts. [ABSTRACT FROM AUTHOR]

The slow kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in air cathodes severely limit the development of reversible zinc–air batteries. Thus, bifunctional oxygen catalysts with excellent electrocatalytic activity and durability for both the oxygen reduction and oxygen evolution reactions (ORR/OER) are keys to achieving long-term rechargeable zinc–air batteries. However, it remains challenging to further improve the performance by adding more active sites. To address this, a series of nitrogen-doped carbon (CN) with NiCo alloys has been synthesized by pyrolyzing a simple bimetal zeolitic-imidazolate framework (ZIF) and then evenly loaded with metallic Ru nanoparticles, resulting in Ru–NiCo/NC samples. Benefiting from the large pore volume and high activities, the Ru–NiCo/NC electrocatalysts exhibit higher ORR (E1/2 = 0.84 V) and OER performance with an overpotential of 342 mV at 10 mA cm−2, along with superior cycle stability. More significantly, when employed in rechargeable zinc–air batteries, Ru–NiCo/NC catalysts demonstrate a high power density of 132.3 mW cm−2, significantly outperforming Pt and Ru-based zinc–air batteries. Additionally, DFT (density functional theory) results indicate that the addition of Ru leads to a downshift of the d-band center from the Fermi level, which benefits the reduction of energy barriers and enhances the desorption of O-containing intermediates. This work provides a feasible strategy for developing efficient and high-performance bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

For effective overall water splitting (OWS) in alkaline media, a novel Ru-doped bimetal oxide (Ru-NiCo2O4) catalyst deposited onto a conductive nickel foam (NF) is fabricated by a multi-step hydrothermal reaction, ion exchange, and subsequent annealing process. The distinctive 3D nanoneedle-like arrays not only provide an even distribution of Ru decorated NiCo2O4, but also expose additional active sites, facilitating electron transport and improving reaction kinetics. Besides, density functional theory (DFT) studies elucidate the electronic structure regulation in Ru-NiCo2O4 and the modification of the d-band center optimizes H* adsorption energy, which considerably increased the hydrogen production efficiency. Considering the aforementioned advantages, the as-prepared Ru-NiCo2O4 electrocatalyst exhibits greatly improved catalytic activity, requiring only 25 mV and 249 mV at 10 mA cm−2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, as well as robust stability. Amazingly, the Ru-NiCo2O4 electrode in a two-electrode alkaline electrolyzer only needs 1.55 V to produce 10 mA cm−2, making it more efficient than the commercial RuO2‖‖Pt/C electrode (1.62 V). More importantly, 0.33 M urea only needs a low voltage of 1.427 V to drive the urine-mediated electrolysis, which is about 123 mV less than the urea-free electrolysis cell. This work presents an effective electronic structure engineering approach based on heteroatom doping that may be extended to design and fabricate novel high-performance OWS catalysts. [ABSTRACT FROM AUTHOR]

Photoinduced electron-separation and -transport processes are two independent crucial factors for determining the efficiency of photocatalytic hydrogen production. Herein, a sulfur vacancy defect-decorated CoSx@In2S3 (CoSx@VS-In2S3) core/shell heterojunction photocatalyst was synthesized via an in situ sulfidation method followed by a liquid-phase corrosion process. Photocatalytic hydrogen evolution experiments showed that the CoSx@VS-In2S3 nanohybrids delivered an attractive photocatalytic activity of 4.136 mmol h−1 g−1 under visible-light irradiation, which was 8.23 times higher than that of the pristine In2S3 samples. As expected, VS could enhance the charge-separation efficiency of In2S3 through rearranging the electrons of the In2S3 basal plane, in addition to improving the electron-transfer efficiency, as visually verified by transient absorption spectroscopy. Mechanism studies based on density functional theory calculations confirmed that the In atoms adjacent to VS played a key role in the translation, rotation, and transformation of electrons for water reduction. This scalable strategy focused on defect engineering paves a new avenue for the design and assembly of 2D core/shell heterostructures for efficient and robust water-splitting photocatalysts. [ABSTRACT FROM AUTHOR]

The Co-based heterojunction is regarded as an efficient material for the oxygen evolution reaction (OER), but the synthesis is still time- and labor-consuming, and environmentally unfriendly. Herein, we propose a green and facile L -lysine-induced strategy for the successful synthesis of porous CoS/Co3O4 nanoframes (NFs). L -Lysine played a pivotal role in facilitating the formation of the stable Co(OH)2 nanosheet precursor, which was subsequently in situ converted into CoS/Co3O4 NFs through the sulfuration treatment. The resulting CoS/Co3O4 NFs showed a low overpotential of 304 mV at 10 mA cm−2 and remarkable long-range durability in 1.0 M KOH for the OER. The rechargeable Zn–air battery exhibited high charge–discharge cycling stability (>120 h) with CoS/Co3O4 NFs + Pt/C as an air cathode. Density functional theory calculations demonstrated that the charge density of the CoS/Co3O4 heterostructure can be redistributed by rebalancing the Fermi level after the contact between CoS and Co3O4, potentially modulating the pristine catalytic properties of single components. This work provides a facile and green synthesis strategy for developing efficient Co-based catalysts in sustainable energy conversion devices. [ABSTRACT FROM AUTHOR]

The aggravating extreme climate changes and environmental pollution problems have stimulated the exploration of green alternatives to conventional fossil fuels and green environmental treatments. Photocatalysis is recognized as an outstanding green tool for solving the energy crisis and environmental rehabilitation issues. Restricted by the high cost of precious metals, researchers expect to obtain low-cost, efficient and stable photocatalysts. Herein, CdS materials were derived through MOFs and subsequently combined with CoO to form CdS/CoO heterojunctions. The catalytic ability was evaluated by the photocatalytic degradation of tetracycline hydrochloride (TC) and the photocatalytic production of hydrogen. With the integration of CoO, in terms of TC degradation, CdS/CoO heterojunctions can degrade over 90% of TC within 1 hour. In terms of hydrogen production, compared to CdS alone, the hydrogen production efficiency of the CdS/CoO heterojunction increased by 1.7 times. The initial analysis of the reasons for the enhancement of photocatalytic efficiency was conducted by TEM, XPS and other characterization means. Density functional theory (DFT) calculations verified the existence of a built-in electric field in the CdS/CoO heterojunction, which was the essential reason for the improved catalytic performance, and finally, the presence of ˙O2− and ˙OH in the photocatalytic system was demonstrated by the ESR technique. Based on the carrier separation/transfer pathway in the heterojunction, a simple and novel S-type heterojunction scheme was proposed. [ABSTRACT FROM AUTHOR]

The development of new, efficient noble-metal-free photocatalysts is of great significance for the photocatalytic hydrogen evolution reaction. Herein, Co9S8 with a hollow polyhedral structure was synthesized by in situ sulfurization of ZIF-67, and subsequently, Co9S8@Ni2P composite photocatalytic materials were prepared by loading Ni2P on the surface of Co9S8 through a solvothermal method based on a morphology regulation strategy. The design of the 3D@0D spatial structure of Co9S8@Ni2P is favorable for the formation of photocatalytic hydrogen evolution active sites. Due to the excellent metal conductivity of Ni2P, Ni2P as a cocatalyst can accelerate the separation of photogenerated electrons from holes in Co9S8, thus providing a large number of available photogenerated electrons for photocatalytic reactions. It is worth mentioning that a Co–P chemical bond is formed between Co9S8 and Ni2P, which plays an active role in the transport of photogenerated electrons. The densities of states of Co9S8 and Ni2P were determined by density functional theory (DFT) calculations. The reduction of the hydrogen evolution overpotential and the formation of efficient charge-carrier transport channels on Co9S8@Ni2P were confirmed by a series of electrochemical and fluorescence tests. This study provides a new idea for the design of highly active noble-metal-free materials for the photocatalytic hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Focusing on renewable energy, we developed an efficient and robust catalyst for overall water splitting (OWS). Using density functional theory (DFT) as the guide, a combination electrode with bifunctional activities based on Co-based carbonate hydroxides (CCHs) and pyrenely-graphdiyne nanowalls (Pyr-GDY-NWs) with three-dimensional structures was designed, and then a series of experiments were attempted to prepare the combination electrode CCH@Pyr-GDY-NWs. From the data of theory and experiment, we found that the combination electrode CCH@Pyr-GDY-NWs exhibits an outstanding catalytic activity towards OWS. The design approach reported herein could open up a new avenue for the construction of three-dimensional Pyr-GDY-NW-based electrodes with high catalytic activity. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting as an important means of obtaining high purity hydrogen fuel has attracted great interest. In this study, the structural engineering of complex WNiM–WNi LDH (M = Se, S, or P) was firstly developed by in situ growth on Ni foam for use in overall water splitting and the urea oxidation reaction. These WNiM–WNi LDH (M = Se, S, or P) catalysts exhibit outstanding electrocatalytic performance in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR), respectively. An overpotential of only 64 mV of OER is required for WNiS–WNi LDH and 126 mV of HER is required for WNiP–WNi LDH to achieve 10 mA cm−2. The WNiSe–WNi LDH materials display a particularly outstanding performance for UOR, requiring a potential of 1.25 V to drive 10 mA cm−2. Moreover, the optimized WNiS–WNi LDH as an anode and WNiP–WNi LDH as a cathode can achieve 10 mA cm−2 at a low cell voltage of 1.45 V in 1 M KOH solution for overall water splitting. The density functional theory calculations show that the introduction of the NiP2 and WP material greatly reduces the Gibbs free energy of the hydrogen adsorption of the material. [ABSTRACT FROM AUTHOR]

Developing highly efficient electrocatalysts is crucially significant for the application of advanced energy conversion. The Fe–N–C single-atom catalyst is promising for CO2 electroreduction reaction (CO2RR) but suffers from insufficient intrinsic activity and inferior conductivity, which could be addressed by redistributing the electron density via heteroatom doping. Herein, we synthesized S-doped Fe–N–C (Fe–SN–C) as an advanced electrocatalyst for CO2RR using a simple trapping–pyrolysis strategy. Density functional theory calculations and experimental results indicate that S doping increases the d-band electrons and conductivity of Fe–SN–C by electron donating, and thus boosts *CO desorption during the CO2RR process and suppresses the competing hydrogen evolution reaction. Consequently, Fe–SN–C exhibits the maximum CO faradaic efficiency of 93% at −0.5 V and the highest partial current density of 10.1 mA cm−2 at −0.8 V for 2e− CO2RR. This finding provides a feasible and controllable method to achieve advanced electrocatalysts for efficient energy conversion. [ABSTRACT FROM AUTHOR]

Electrocatalyst design is an important approach to prompt the commercialization of water electrolysis technologies. In this work, a ruthenium doped MoS2/AB heterostructure is synthesized as an electrocatalyst for the hydrogen evolution reaction (HER) through hydrothermal and annealing processes. The physical–chemical characterization studies show that the MoS2/AB heterostructure and the incorporation of Ru effectively induce a phase transition from 2H to 1T-MoS2. The as-prepared Ru-MoS2/AB exhibits an excellent HER performance with a very low overpotential of 13 mV at 10 mA cm−2 and a Tafel slope of 31 mV dec−1 in 0.5 M H2SO4, remarkably higher than those of Pt/C (overpotential of 28 mV at 10 mA cm−2, 41 mV dec−1). Density functional theory calculations suggest that the H absorption on Ru bonding to S exhibits a rather low binding energy (−0.22 eV), indicating the optimum active sites of Ru near S for HER. Significantly, the Ru-MoS2/AB also demonstrates high stability under long-term discharge and elevated temperature conditions. These results suggest that the as-prepared Ru-MoS2/AB can be a promising alternative to Pt/C for water electrolysis, due to its high HER activity, easy synthesis, and good stability. [ABSTRACT FROM AUTHOR]

We report a joint experimental and theoretical study of RuO2/TiO2 heterostructures. In the experimental section, mesoporous RuO2/TiO2 heterostructures were prepared by impregnation of mesoporous TiO2 nanoparticles which were synthesized from a new precursor, Na2[Ti(C2O4)3], in an aqueous solution of ruthenium(III) chloride followed by calcination at 300 °C. Using various techniques, the prepared TiO2 and RuO2/TiO2 heterostructures were extensively characterized. The photoelectocatalytic application of the as-prepared heterostructures was then investigated toward the hydrogen evolution reaction (HER). The results illustrated that RuO2 is dispersed uniformly on the TiO2 surface. The loading of RuO2 on TiO2 decreases the band gap energy and extends the absorption edge to the visible light region. This wide absorption extends the photoelectrocatalytic activity of RuO2/TiO2 heterostructures. To obtain a deeper understanding of the increase of the photoelectrocatalytic activity of RuO2/TiO2 heterostructures compared to pure TiO2, theoretical calculations at the density functional theory (DFT) level were performed on some model clusters of pure TiO2 and the RuO2/TiO2 heterostructure. The theoretical results elucidated that the recombination ratio of electron–hole pairs decreases effectively for RuO2/TiO2 compared to pure TiO2. [ABSTRACT FROM AUTHOR]

Single-atom catalysis is a new field that has developed rapidly in recent years and has greatly helped the development of catalytic science. We have processed a large amount of literature data through the Web of Science database. The bibliometric method was used to analyze the development trend and research hotspots over the past 10 years since the concept of single-atom catalysis was proposed in 2011. Results show that the field of single-atom catalysis is currently at a high-speed development stage. China is in a leading position in terms of comprehensive strength, with the largest number of publications and great influence. Most productive journals and institutions are ACS Catalysis and Chinese Acad. Sci. Single-atom catalysis has the most research results in the field of chemistry. In addition, the most commonly used keywords are "density functional theory", "oxygen reduction reaction", "electrocatalysis", "co oxidation", "graphene", "heterogeneous catalysis", "platinum", "hydrogen evolution reaction", which reflect the research direction of the current field. This article reviews the main research content of single-atom catalysts in order to facilitate researchers understanding the current situation in the field, and to also provide some guidance for future research. [ABSTRACT FROM AUTHOR]

The development of earth-rich, low-cost, and high-efficiency electrocatalysts toward alkaline hydrogen evolution reactions (HERs) in the water spitting process is extremely desirable yet a huge challenge. In this work, we report the synthesis of novel RuO2/MoS2 electrocatalysts with good conductivity and abundant active sites for efficient HER by uniformly dispersing RuO2 nanoparticles on MoS2 nanosheets. Benefitting from the intense electronic coupling effect endowed with interface modifications, the as-prepared RuO2/MoS2 electrocatalysts exhibited superior performance for HER in 1 M KOH with a very low overpotential of 36 mV at 10 mA cm−2 and a small Tafel slope value of 34.8 mV dec−1. Moreover, the introduction of RuO2 nanoparticles improved the durability of the RuO2/MoS2 electrocatalysts with negligible variation in a 20 h operation. More importantly, the density functional theory (DFT) calculations further revealed the mechanism of strong electronic interaction between RuO2 nanoparticles and MoS2 nanosheets, which contributes to accelerating the H2O dissociation kinetics and optimizing H adsorption Gibbs free energy. This work may provide a deeper understanding for designing efficient HER catalysts through interface modification strategies. [ABSTRACT FROM AUTHOR]

Urea splitting is a highly promising technology for hydrogen production to cope with the fossil energy crisis, which requires the development of catalysts with high electrocatalytic activity. In this article, Crx–FeCo2P/NF catalysts were synthesized by hydrothermal and low-temperature phosphorylation and used in the overall urea splitting process. Cr0.15–FeCo2P/NF and Cr0.1–FeCo2P/NF exhibited excellent urea oxidation reaction (UOR) activity (potential of 1.355 V at 100 mA cm−2) and hydrogen evolution reaction (HER) activity (overpotential of 173 mV at 10 mA cm−2) in 0.5 M urea solution containing 1 M KOH. In the assembled Cr0.15–FeCo2P/NF//Cr0.1–FeCo2P/NF electrolytic cell, only a small voltage of 1.50 V is needed to reach 10 mA cm−2. Density functional theory (DFT) calculation results demonstrate that an appropriate amount of Cr doping accelerates the kinetic performance of hydrogen production as well as improving the metallic properties of the electrode. [ABSTRACT FROM AUTHOR]

The development of substantial, environment-friendly and low-cost electrocatalysts for an efficient oxygen reduction reaction (ORR) is essentially important for the production and storage of green energy which has sparked the curiosity of researchers for scalable production of metal-free electrocatalysts from biowaste. We report an easy transformation of chestnut-derived biowaste into reduced graphene oxide (rGO) and pyridinic-N-dominated nitrogen-doped rGO (NCS-rGO). The synthesized catalyst exhibits better ORR activity with an onset and half-wave potential of 0.93 V and 0.86 V, respectively, along with a high diffusion-limiting current density of 5.05 mA cm−2. Under alkaline conditions, we found that NCS-rGO shows an unusually high electrocatalytic activity that is superior to that of the commercial 20% Pt/C catalyst. More notably, the NCS-rGO-based ORR electrocatalyst manifests higher methanol tolerance, without deterioration in catalytic activity even in the presence of significant amount of methanol, outperforming the current state-of-the-art Pt electrocatalyst. Density functional theory (DFT) studies illustrate that pyridinic N is a decisive part of NCS-rGO to achieve the best ORR performance. [ABSTRACT FROM AUTHOR]

Cocatalysts are usually applied in the photocatalytic water splitting process to accelerate the kinetics of the hydrogen evolution reaction (HER). Specifically, the transition metal nitride (Mo2N) featuring a unique local surface plasmon resonance (LSPR) effect has exhibited great potential to function as a HER cocatalyst. However, the low metallicity of Mo2N hampers its ability to improve charge separation. To address this issue, transition metal atom doping (Co and Cu) engineering was used to modulate the electronic structure of Mo2N nanosheets to achieve a higher electrical conductivity and a lower hydrogen adsorption free energy (‖ΔGH*‖), thereby favoring the HER kinetics. Density functional theory (DFT) calculations and experimental results showed that Co-doping and Cu-doping mainly take place at Mo sites in the crystal structure of Mo2N to form stable structures of Co doped Mo2N (Co–Mo2N) and Cu doped Mo2N (Cu–Mo2N). Compared with pristine Mo2N, both Cu–Mo2N and Co–Mo2N demonstrated a much improved cocatalytic effect over g-C3N4 in promoting charge separation, accelerating HER kinetics and enhancing light absorption. The Co–Mo2N with the highest conductivity and lowest ‖ΔGH*‖ illustrated the best cocatalytic effect, and the H2 production performance (367.8 μmol g−1 h−1) of Co–Mo2N/g-C3N4 achieved was 10 and 5 times higher than those of Mo2N/g-C3N4 and Cu–Mo2N/g-C3N4. This paper provides significant guidance in the design and development of efficient cocatalysts for the HER application. [ABSTRACT FROM AUTHOR]

Rationally designing ternary transition-metal phosphides (TMPs) for the hydrogen evolution reaction (HER) is desirable but remains a significant challenge. Herein, ternary FeCoNiP encapsulated in a porous carbon shell, coupled with N-doped carbon nanotubes (FeCoNiP@NCNTs) are synthesized via a simple pyrolysis–phosphatization strategy derived from FeCoNi-MOF-100@dicyandiamide. Because Co/Ni enters the FeP lattice, FeCoNiP@NCNTs show a favorable catalytic performance towards the HER with low overpotential values of 86.7 and 233.5 mV at 10 mA cm−2 in acidic and alkaline media, respectively, surpassing the HER performance of FeP@NCNTs, FeCoP@NCNTs, and FeNiP@NCNTs. Impressively, FeCoNiP@NCNTs display adequate acid-resistance capacity during the HER process, with nearly negligible decay due to the thin graphitized carbon shell structure with a thickness of 11.5–20.3 nm. The results of experiments, structural characterization, and density functional theory (DFT) calculations demonstrate that Co/Ni co-doping can modulate the adsorption and dissociation processes of H+ and downshift the d-band center of FeP. This work proposes a strategy for fabricating ternary TMP catalysts with heterogeneous structures for the HER. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have emerged as an extremely promising material for photocatalytic water splitting for hydrogen production. However, their photocatalytic performance is seriously affected by the properties of their donors, acceptors and linkages. So far, few studies have been reported on the key roles of the linkages of a specific COF in improving its photocatalytic hydrogen production performance. Herein, this study designed and synthesized two thiadiazole-based COFs linked by imine and alkyne bonds. The results show that the photocatalytic hydrogen production performance of imine-linked COFs (TeTz–COF1) is 19.6 times higher than that of alkyne-linked COFs (TeTz–COF2). Impressively, TeTz–COF1 achieves an apparent quantum efficiency of 3.5% at 475 nm due to the presence of imine bonds. The experimental results confirm that TeTz–COF1 with imine linkages shows higher photocurrent density, lower photocurrent resistance, and longer fluorescence lifetime than TeTz–COF2 with alkyne linkages. Meanwhile, the well-defined density functional theory (DFT) calculations further suggest that both the imine bond and the acetylene bond belong to the HOMO orbitals. Particularly, the imine bonds endow TeTz–COF1 with more delocalized orbital occupation and smaller work functions, thus leading to its lower excited state energy, stronger carrier separation ability and faster electron migration capability. Both theoretical analysis and the experimental results prove that the presence of imine bonds in TeTz–COF1 can enable the efficient separation and fast transport of photogenerated carriers and high reducing ability of photogenerated electrons. This work may provide important guiding significance for the development of new COFs in the direction of photocatalytic water splitting for hydrogen production. [ABSTRACT FROM AUTHOR]

The preparation of low-cost and high-activity oxygen evolution reaction (OER) catalysts is a technical bottleneck in the field of electrolysis of water to produce hydrogen. Amorphous metal–organic frameworks (MOFs) with low-cost transition metals have attracted increasing attention in the catalytic field, yet metal atoms that are the main active sites are still ambiguous. Here, we synthesized a series of amorphous ternary Fex(NiCu)3−x-MOFs via an ultrasonic method. The optimal amorphous FeNiCu-MOF is found to be able to supply a current density of 10 mA cm−2 merely at a low overpotential of 260 mV with a small Tafel slope of 61 mV dec−1 and exhibits high durability over 24 h. Moreover, density functional theory (DFT) calculations show that the Fe atoms are the main active sites for the OER in the FeNiCu-MOF. This work shows that amorphous ternary MOFs have great potential for application in OER electrocatalysts due to the multiple synergistic effects and amorphous MOF structures. [ABSTRACT FROM AUTHOR]

Urea electrolysis is of great interest for energy-related applications, but it is limited by a complex six-electron transfer process with slow kinetics. Herein, the in situ growth of Cr-doped Co2P homogeneous nanoneedle arrays on nickel foam substrates (Cr-Co2P/NF) was reported for the first time by a typical hydrothermal and low-temperature phosphorization process. The appropriate amount of Cr doping was found to promote the electronic modulation of active centers and the expansion of the specific active surface area, resulting in the superior performance of the urea oxidation reaction (UOR). It is noteworthy that Cr0.4-Co2P/NF exhibited a superior performance of the UOR at an onset potential of 1.290 V and a cell voltage of 1.333 V at 50 mA cm−2 in 1 M KOH containing 0.5 M urea, which is one of the best catalytic activities reported so far. The experimental results demonstrate that the enhanced catalytic activity can be attributed to favorable electronic regulation, an improved charge transfer rate and increased exposure to active sites. Density functional theory (DFT) calculation indicates that the appropriate doping of Cr effectively regulates and controls the adsorption energy of urea and the conductivity of the Co2P material itself. This work provides new ideas for the development of robust catalysts for the electrolysis of urea through doping strategies. [ABSTRACT FROM AUTHOR]

For energy conversion and storage, the electrochemical oxygen evolution process (OER) is the crucial half-reaction process. The amphiprotic characteristics of sulfamic acid are due to its amine and sulphonic acid functional groups. Metal-based catalysts can be utilized to fabricate bimetallic and dual-ligand linked FeCo–SA/DABCO nanosheets with improved catalytic performance. The crystal structure of bimetallic FeCo–SA/DABCO consisted of alternating organic hydrocarbons SA and DABCO and inorganic metal–oxygen layers. FeCo–SA/DABCO provided an overpotential (η10) of 290 mV to achieve a current density of 10 mA cm−2 together with a small Tafel slope of 112.79 mV dec−1 and also exhibited long-term durability. Electrochemical results showed that FeCo–SA/DABCO was superior to FeCo–SA and Co–SA/DABCO. Density functional theory calculations indicated that the theoretical overpotential of FeCo–SA/DABCO is 0.62 eV, which was lower than that of FeCo–SA. The introduction of composite SA/DABCO ligands can change the rate-determining step, which can improve the conductivity and reduce the reaction barrier for the formation of intermediates, thereby affecting the catalytic activity and changing the overall electron transfer capacity. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2)-based transition-metal chalcogenides are considered to be cost-efficient, environmentally-friendly, and stable materials in the application of electrocatalytic hydrogen production. However, the low density and poor reactivity of active sites within the basal plane of MoS2 hinder hydrogen evolution reaction (HER). Herein, we reported that N, P co-doped in the basal plane of MoS2 (N, P-MoS2) can convert the parts of 2H MoS2 to 1T MoS2 and enlarge interlayer spacing for an efficient HER. Subsequently, electrochemical tests revealed that N, P-MoS2 showed an overpotential of 179 mV at 10 mA cm−2, a corresponding Tafel slope of 143 mV dec−1, and remarkable long-term stability over 20 h. In addition, we combined these findings with theoretical results from density functional theory (DFT) simulations. The results confirmed that the synergistic effect of N and P activated the HER catalytic activity at the edge of N-MoS2. In short, the synergy improved the conductivity of N-MoS2 and promoted the rapid transfer of charge to achieve high-performance HER activity. The work provides new insight into the synergistic effect of N and P co-doped in the basal plane of MoS2, as well as a new pathway for the rational design of efficient HER electrocatalysts. [ABSTRACT FROM AUTHOR]

We present here the influence of different surface terminations on the electronic, optical, and photocatalytic properties of trans and cis BaTaO2N using density functional theory calculations. For each surface, we consider two complementary terminations exposed with Ba and Ta atoms, respectively. The calculated surface energies suggest that (001) and (100) are more stable than other low-index surfaces. Work functions are distinct for various surface terminations, which can be attributed to the atomic displacements in different directions and degrees after relaxation. We propose that the transferring direction of the photogenerated carriers in BaTaO2N-based heterostructures could be controlled by obtaining the preferred surface termination. The simulated absorption spectra suggest that both trans and cis BaTaO2N exhibit optical anisotropy, which could result from the difference in relaxed crystal parameters along different directions. Dissociative water adsorption on both the (001) and (100) terminations is thermodynamically favorable. The hydrogen evolution reaction (HER) is easier to occur on the terminations exposed with Ta, O, and N simultaneously. The computed overpotentials of oxygen evolution reaction (OER) for trans-(001)-BaO, cis-(001)-TaON, cis-(001)-BaO, and cis-(100)-Ta2O3N are in good agreement with the experimental results. These findings provide important insights into the rational design of (001)- and (100)-oriented BaTaO2N samples for enhanced photocatalytic activity. [ABSTRACT FROM AUTHOR]

The approach of artificial photosynthesis involves the use of water and sunlight to achieve the photoreduction of CO2 into carbohydrates. Herein, the GaSe monolayer is investigated in terms of its structural, electronic and photocatalytic properties via first-principles calculations towards water splitting and artificial photosynthesis. The mechanical and dynamical stability of the GaSe monolayer was affirmed according to the Born–Huang mechanical stability conditions and phonon band structure, respectively. The GaSe monolayer has an indirect bandgap value of 2.92 eV, with band edges that straddle the water redox and CO2 reduction potentials. Consequently, the GaSe monolayer is a potential photocatalyst for water splitting and CO2 photoreduction over a wide pH range of 0–14. Moreover, a high electron and hole mobility was obtained, which is more significant compared to a 2D MoS2 monolayer. To improve its photocatalytic performance, the GaSe monolayer was investigated in-depth under biaxial tensile and compressive strain. Interestingly, the optimum strain values for water splitting and CO2 photoreductions are 5% and 4%, respectively, owing to their band edges in the vicinity of the redox potentials. Moreover, the GaSe monolayer under 3% tensile strain has a Gibb's free energy for hydrogen adsorption (ΔGH) value of close to 0 eV, making it a promising photocatalyst for hydrogen evolution reaction (HER) activity. Moreover, the strain-induced monolayers have absorption coefficients on the order of 105 cm−1, making the material a potential candidate for solar energy harvesting. Our study suggests that the effect of biaxial strain on these types of transition metal monochalcogenides can be explored experimentally to develop an excellent photocatalyst for use in photocatalytic water splitting and artificial photosynthesis applications. [ABSTRACT FROM AUTHOR]

Pd-based nanocatalysts are critical to the commercialization of direct ethanol fuel cells (DEFCs); however, the synthesis of Pd-based binary alloy nanocrystals with well-defined branches is still a great challenge. Here we report a facile seed-mediated approach for the synthesis of PdSn alloy octopods with precisely controlled branches and tunable compositions through the Stranski–Krastanov growth mode. The PdSn octopod-like catalysts exhibited prominently enhanced catalytic activity and stability towards the ethanol oxidation reaction (EOR) with respect to commercial Pd/C in alkaline solution. Specifically, Pd72Sn28 octopods exhibited the highest mass and specific activities (2701 mA mg−1 and 11.27 mA cm−2), which were 2.1 and 6.7 times higher than those of commercial Pd/C, respectively. Density functional theory (DFT) calculations reveal that the lowest d-band center of the (100) surface of Pd72Sn28 weakens the adsorption of the acetate-evolution key intermediate *CH3CO, leading to the best catalytic activity towards the EOR. [ABSTRACT FROM AUTHOR]

Producing molecular hydrogen (H2) using water provides a sustainable approach for developing clean energy technologies. Herein, we report highly active ruthenium (Ru) clusters supported on iron oxide (Ru/Fe3O4) and Fe3O4/multi-walled carbon nanotubes (Ru/Fe3O4/MWCNTs) by simple electrochemical deposition in a neutral aqueous medium. The supported catalyst exhibits good hydrogen evolution reaction (HER) activity in an acidic environment. Cyclic voltammograms (CVs) of potassium ferrocyanide (K4[Fe(CN)6]) confirm that MWCNTs enhance the electron transfer process by decreasing the redox formal potential. The overpotentials of Ru/Fe3O4/MWCNTs and Ru/Fe3O4 electrocatalysts versus the reversible hydrogen electrode (RHE) were found to be 101 mV and 306 mV to reach a current density of 10 mA cm−2. As prepared, the catalyst displays good stability and retain its HER activity even after 1000 cycles. Furthermore, the stability of Ru/Fe3O4/MWCNTs was studied using the chronopotentiometric (CP) technique for 12 h and found negligible loss in the catalytic activity towards the HER. To explore the role of Ru and underneath MWCNTs in improving the catalytic performance of Fe3O4, density functional theory (DFT) calculations were carried out. DFT calculations indicate that the octahedral site of Ru/Fe3O4 favors the HER with a low overpotential. However, Ru/Fe3O4/MWCNTs are more efficient towards the HER, which could be due to the availability of both octahedral and tetrahedral catalytic sites. [ABSTRACT FROM AUTHOR]

Generation of molecular hydrogen by electrochemical water splitting is a promising approach, and its efficiency strictly depends on the electrocatalyst used. Therefore, it is an ongoing challenge to design materials having improved the electrocatalytic behaviour towards hydrogen evolution reaction. Here, using Co-MOF [Co4(BTC)3(BIm)6] as starting precursor, graphitic carbon encapsulated CoSe2 nanorods have been prepared through a single step selenization method. The carbon network in the CoSe2/C hybrid nanostructure forms channels, facilitating the accessibility of the electrolyte ions and maximizing the utilization of catalytic active centers. This makes the hybrid to show higher electrochemical accessible surface area, lower charge transfer resistance, and improved catalytic durability towards the electrocatalytic hydrogen evolution reaction with respect to the non-noble metal (graphite rod) counter electrode. Specifically, it needs only 253 mV of overpotential to reach the benchmarked current density (10 mA cm−2) with a lower Tafel slope. Further, the experimental findings have been supported by the theoretical analysis of the structure and electronic properties of CoSe2 and CoSe2/C hybrid by density functional theory (DFT) simulations. The interaction between CoSe2 and C is due to charge transfer from Co 3d orbital and Se 4p orbital of CoSe2 to the 2p orbital of carbon. Also, populated electronic states near Fermi level for C doped CoSe2 may infer towards increased conductivity of the material. Computed overpotentials for HER activities show a qualitative order of CoSe2/C < CoSe2, matching nicely with the experimental data. The synergic effect of increased conductivity, improved surface area, and superior electrocatalytic activity due to C doping is responsible for the superior HER catalytic performance. [ABSTRACT FROM AUTHOR]

Sluggish charge transfer is the major problem which restricts the development of metal–organic framework (MOF)-based photocatalysts. Recently, facet-engineering has been proven to be an effective method for solving this issue. However, due to difficulties in regulating the exposed facets of MOFs, there are few reports about the facet-engineering of MOF-based photocatalysts. Here, we firstly report facet-engineering for promoting the photocatalytic activity of NH2-UiO-66 crystals. In this study, by regulating the influence of kinetics and thermodynamics, cubic, tetra-decahedral, and octahedral forms of NH2-UiO-66 are synthesized. The photocatalytic hydrogen evolution rate of tetra-decahedral NH2-UiO-66 with co-exposed (100) and (111) crystal facets reaches 64.06 μmol g−1 h−1, which is approximately 2 and 1.5 times greater than that of the cubic and octahedral forms of NH2-UiO-66, respectively. The density functional theory (DFT) calculation and ultrafast spectroscopy results indicate that a slight staggering exists in the band structure of (100) and (111) facets, causing the facets junction to appear. The facet junction promotes the charge separation efficiency and prolongs the lifetime of the charge carriers, thereby giving tetra-decahedral NH2-UiO-66 optimal photocatalytic performance. This study demonstrates the feasibility and potential of facet-engineering for photocatalytic applications of MOFs. [ABSTRACT FROM AUTHOR]

The design and synthesis of hybrid core–shell catalysts is of great significance for obtaining an excellent performance of hydrogen evolution reaction (HER). However, it remains a challenge to explore the exact active sites and research the catalytic mechanism for HER. Here, a series of Ni3S2@MOOH/NF (M = Fe, Ni, Cu, Mn and Co) hybrid structures is firstly in-site grown on Ni foam by the typical hydrothermal and electrodeposition methods. The Ni3S2@NiOOH/NF catalyst with a core–shell structure exhibits a relatively low overpotential of 79 mV for HER at a current density of 10 mA cm−2, which is one of the best catalytic activities reported so far. Moreover, it also shows good stability in the long-term durability test. Various spectral analysis and density functional theory calculations demonstrate that NiOOH is favorable for the adsorption of water molecules, and the S atom at the interface between Ni3S2 and NiOOH is favorable for the adsorption of H intermediates, which strongly accelerates the HER process in alkaline solution. This work provides a general strategy for the synthesis of electrocatalytic materials, which can be used for efficient electrocatalytic water splitting reactions. [ABSTRACT FROM AUTHOR]

Many titanium-oxo clusters (TOCs) with various structure types have been reported, but research on co-crystallized TOCs still remains very rare. Herein, we successfully isolated heterometallic {Ti8Ni4+ Ti4Ni2} with co-crystal arrangement. Because of the Ni-to-TiO and Ti4Ni2-to-Ti8Ni4 charge transfer, cluster {Ti8Ni4+ Ti4Ni2} shows wide light absorption and narrow band gap based on the ultraviolet-visible spectra and density functional theory calculations. Moreover, the cluster co-crystallization and more metal centers in cluster {Ti8Ni4+ Ti4Ni2} endow it with better photocurrent response and photocatalytic hydrogen evolution activity than {Ti4Ni2} alone. This work not only provides a new model for co-crystallized TOCs but also stimulates research interest in their photochemical performances. [ABSTRACT FROM AUTHOR]

Exploiting environmentally friendly and robust electrocatalysts for overall water splitting is of utmost importance in order to alleviate the excessive global energy consumption and climate change. Herein, a simple phosphoselenization method was used to prepare Co2P and CoSe2 coupled nanosheet and nanoneedle composite materials on nickel foam (Co2P/CoSe2/NF). Density functional theory calculations showed that Co2P had a higher water adsorption energy compared with CoSe2, indicating that H2O molecules are strongly adsorbed on the active sites of Co2P, which speeds up the kinetic process of water splitting. The Co2P/CoSe2-300 material displayed superior electrocatalytic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline medium. It's worth noting that the Co2P/CoSe2-300 composite material nanoarrays merely needed an ultralow overpotential of 280 mV to drive a current intensity of 100 mA cm−2 for OER. In addition, when a two-electrode system was constructed for overall water splitting, the current intensity of 20 mA cm−2 could be reached while requiring an ultrasmall cell voltage of 1.52 V, which is one of the best catalytic activities reported up to now. Experimental and density functional theory calculations showed that the superior electrocatalytic performance of Co2P/CoSe2-300 could be attributed to its higher electron-transfer rate, higher water adsorption energy, and the synergistic effect of Co2P and CoSe2. Our work provides a novel approach for the one-step construction of composite materials as environmentally friendly and inexpensive water splitting catalysts. [ABSTRACT FROM AUTHOR]

MoS2 nanosheets were developed by undertaking the liquid-phase exfoliation of bulk counterparts. In order to enhance its photocatalytic properties, the host material was doped with p-type transition metals (i.e., Ag, Co, Bi, and Zr). The hydrothermal technique was used to produce samples doped with 7.5 wt% transition metals (TM). X-ray diffraction detected the existence of 2H-phase by mirroring its reflection at 2 ∼ 14°, while the peak distribution revealed the degree of exfoliation in samples. Low PL intensities indicated a lower recombination of electron–hole pairs, as corroborated by a high degree of photocatalytic action. Raman analysis was undertaken to identify molecular vibrations. The A1g mode in Raman spectra consistently showed a blueshift in all samples and the E12g mode was only slightly affected, which is evidence of the p-type doping in the MoS2 nanosheets. In the XPS spectrum, two characteristic peaks of Mo 3d appeared at 229.87 and 233.03 eV assigned to Mo-3d5/2 and Mo-3d3/2, respectively. Furthermore, a microstructural examination with HR-TEM and FESEM divulged a thin-layered structure of MoS2 consisting of flat, gently curved or twisted nanosheets. Diverse morphologies were observed with a non-uniform distribution of the dopant. Photocatalytic action of the TM-doped products effectively degraded methylene blue (MB) concentrations of up to 94 percent (for Ag-MoS2). The synergistic effect of doped MoS2 nanosheets against S. aureus in comparison to E. coli bacteria was also evaluated. The efficacy % age improved from (0–31.7%) and (23.5–55.2%) against E. coli, and (0–34.2%) and (8.3–69.23%) against S. aureus. Moreover, results from first principles calculations indicate that substitutional doping of TM atoms is indeed advantageous. Theoretical calculations confirmed that doping with Ag, Co, Bi, and Zr leads to a decrease in the band gap to a certain degree, in which the conduction band edge shifts toward lower energy, while the valence band shifts closer to the high energy end. It can be concluded that Ag, Co, and Bi impurities can lead to beneficial p-type doping in MoS2 monolayered structures. With regards to doping with Zr, the acceptor levels are formed above the edge of the valence band, revealing an introduction of the p-type character. [ABSTRACT FROM AUTHOR]

The electrochemical nitrogen reduction reaction (NRR) is currently the most attractive method for ammonia production, in which the development of high efficiency and low-cost electrocatalysts is still a challenge. A lot of recent research has been focused on B single-atom catalysts. However, doping carbon materials with multiple hetero-elements has been rarely explored. Herein, we investigate the catalytic performance of B doped, N doped, and BN co-doped defective graphdiyne (B@GDY, N@GDY and BN@GDY) for nitrogen reduction by using density functional theory. Our results reveal that BN@GDY exhibits higher catalytic efficiency relative to that of single B doping, which is manifested by a significant decrease in overpotential (0.32 V vs. 0.61 V) via the enzymatic mechanism. The projected density of states and Bader charge analysis indicate that BN@GDY can promote the charge transfer from the catalytic substrate to adsorbed N2, in which the addition of N can convert B from sp2 to sp3 hybridization. Meanwhile, the competing hydrogen evolution reaction (HER) can be well inhibited during the NRR for both B/BN@GDY substrates, especially in BN@GDY, indicating the high selectivity of BN@GDY towards the NRR. Above all, this work puts forward a novel metal-free electrocatalyst for the NRR and may provide useful guidance for the design of new non-metal nitrogen reduction electrocatalysts. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting has become one of the state of the art approaches to generate hydrogen. It is important to exploit relatively low toxicity, low cost and environmentally friendly water splitting electrocatalysts. A series of Cu–Ni–M (M = S, P and Se) materials were firstly in situ grown on Ni foam and these materials showed excellent water splitting activity. The Cu–Ni–S material shows excellent oxygen evolution reaction performance (200 mV@20 mA cm−2) and the Cu–Ni–P sample shows an effective hydrogen evolution reaction performance (52 mV@10 mA cm−2). When the Cu–Ni–S and Cu–Ni–P materials were assembled into a two-electrode system, the Cu–Ni–S/NF//Cu–Ni–P/NF electrode pairs display superior water splitting activity (1.50 V@20 mA cm−2), which is one of the best electrocatalytic activities reported so far. The experimental analysis demonstrates that the excellent performance of the Cu–Ni–S/NF and Cu–Ni–P/NF materials is attributed to the rapid electron transfer rate, increased electrocatalytically active area, more exposure to active sites and the superior synergistic catalytic factor of Ni2+ and Cu2+. It was found that amorphous oxides were in situ generated on the outside surface of the catalyst through the analysis of the catalyst after the reaction, and they were the real electrocatalytically active centers. Density functional theory demonstrates that the in situ generated Cu-doped NiOOH shows the optimal water adsorption energy compared with NiOOH. This work offers novel views for the design of relatively low toxicity, stable and inexpensive water splitting electrocatalysts. [ABSTRACT FROM AUTHOR]

Although Ni phosphides are efficient for hydrogen evolution reactions, they are unfavorable for oxygen evolution reactions, so their application in alkaline water electrolysis is limited. It is a feasible method for creating a novel Ni phosphide/oxide heterogeneous interface to promote the oxygen evolution kinetics of Ni phosphide materials in an alkaline medium, yet it has been an unprecedented challenge for researchers. In this work, NiP3@CeO2 hybrid nanoparticles are firstly in situ grown on Ni foam (NiP3@CeO2/NF) via a novel controlled phosphating strategy. The NiP3@CeO2/NF catalysts display a fairly small overpotential of 200 mV to achieve a current density of 25 mA cm−2 for the oxygen evolution reaction (OER) under alkaline conditions, 110 mV smaller than that of NiO@CeO2/NF. It is noteworthy that the improved electrocatalytic performance of NiP3@CeO2/NF can be attributed to rapid electron transfer and the synergistic catalytic effect of the hybrid material. Density functional theory results demonstrate that NiP3 shows a stronger water adsorption energy than CeO2. The novel strategy of controlled phosphating to construct transition metal phosphide/oxide interfaces provides new ideas and methods for the development of efficient and practical water splitting catalysts. [ABSTRACT FROM AUTHOR]

To focus on renewable energy, we have been devoted to developping energy-efficient, robust and low cost water reduction catalysts (WRCs). Two hybrid inorganic–organic hexa/octa-CuII-sandwiched POM: [Cu(dap)2]2[{Cu8(dap)4(H2O)2} (SiW9O34)2]·7H2O (1) and [Cu(dap)2(H2O)]2[Cu(dap)2]2[{Cu6(dap)2}(SiW9O34)2]·8H2O (2) (dap = 1,2-diaminopropane, 1,4-H2NDC = 1,4-naphthalenedicarboxylic acid) were synthesized under hydrothermal conditions. The new copper complexes were applied as water reduction catalysts (WRCs) in the presence of [Ir(ppy)2(dtbbpy)][PF6] as a photosensitizer and triethanolamine (TEOA) as a sacrificial electron donor. Meanwhile, the number of nuclear substituted polyoxotungstates was the critical factor influencing photocatalysis. The experimental results matched well with the conclusions obtained via density functional theory (DFT). It is noteworthy that our research not only enriches the field of CuII-sandwiched POM chemistry but also provides an investigation of the relationship between photocatalytic activity and the nuclear number of Cu-substituted POMs. These results may guide us to synthesize different nuclear copper-substituted polyoxotungstates and develop their applications toward energy and environmental uses. [ABSTRACT FROM AUTHOR]