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The design of efficient and cost-effective electrocatalysts with steady capability has attracted much attention in the field of water splitting in recent years. In this paper, Ni2−xCoxP/CNFs (x = 0, 0.67, 1, 1.33 and 2), where the ultrafine Ni2−xCoxP nanoparticles are encapsulated in carbon nanofibers, are synthesized using a facile electrospinning method followed by thermal treatment. The space confinement by the carbon matrix with a high length-to-diameter ratio (>1000) and excellent conductivity produces ultrafine Ni2−xCoxP with abundant active sites. Moreover, engineering of Ni2−xCoxP/CNFs can induce electronic modulation and consequently optimize the adsorption of H on the electrocatalyst surface to promote HER performance, as well as to reduce the energy barrier of the potential-limiting step. The optimal Ni2−xCoxP/CNFs exhibit superior electrocatalytic performance with low overpotentials of about 271 mV for OER and about 118.76 mV for HER at 10 mA cm−2 with excellent long-term durability in 1.0 M KOH solutions, performing as one of the best non-noble-metal electrocatalysts so far. Furthermore, the two-electrode electrolyser delivers a high efficiency and remarkable long-term durability for overall water splitting. This work provides new insights into the development of nanofiber-structured electrocatalysts. [ABSTRACT FROM AUTHOR]

The electrocatalytic nitrogen reduction reaction (eNRR) under ambient conditions is deemed a promising alternative for NH3 synthesis. In this paper, an FeP–Fe3O4 nanocomposite electrocatalyst was prepared by phosphating annealing using Fe2O3 as a precursor, and the resulting FeP–Fe3O4 exhibited excellent N2-to-NH3-producing activity over a wide potential window. The highest faradaic efficiency of FeP–Fe3O4 is 11.02% at −0.1 V vs. reversible hydrogen electrode (RHE), and the maximum NH3 yield reaches 12.73 μg h−1 mgcat−1, comparable to or exceeding the reported values in this field. Furthermore, the FeP–Fe3O4 nanocomposite electrocatalyst presents high electrochemical stability, selectivity, and durability. [ABSTRACT FROM AUTHOR]

Platinum-based catalysts exhibit outstanding electrocatalytic performance in the hydrogen evolution reaction (HER). However, platinum-based catalysts face significant challenges due to their rarity and high cost. This paper endeavors to shed light on a promising alternative: polyoxometalate (POM)-based catalysts, which possess significant potential for the synthesis of non-noble metal-based catalysts for the HER. Utilizing POMs as raw materials to assemble POM-derived materials, including POM-derived crystalline materials, metal sulfides, phosphides, carbides, nitrides, and so on, has emerged as an effective approach for the synthesis of hydrogen evolution electrocatalysts. This approach offers advantages in both stability and electrocatalytic performance. This comprehensive review navigates through latest progress in the assembly strategy and HER performance of POM-based crystal materials, alongside discussion on transition metal compounds derived from POMs, such as carbides, phosphides, and sulfides. Besides, future developments in POM-derived electrocatalyst regulation of the electrochemical HER are prospected. [ABSTRACT FROM AUTHOR]

Hydrogen, highly valued for its pristine cleanliness and remarkable efficiency as an emerging energy source, is anticipated to ascend to a preeminent status within the forthcoming energy landscape. Electrocatalytic water splitting is considered a pivotal, eco-friendly, and sustainable strategy for hydrogen production. The substantial energy consumption stemming from oxygen evolution side reactions significantly impedes the commercial viability of water electrolysis. Consequently, the pursuit of a cost-effective and efficacious oxygen evolution reaction (OER) catalyst stands as an imperative strategy for realizing hydrogen production via water electrolysis. Layered metal oxides, owing to their robust anisotropic properties, versatile adjustability, and extensive surface area, have emerged as suitable candidates for OER catalysts. However, owing to the distinctive attributes of layered metal oxides, ongoing investigations into these materials are slightly fragmented, lacking universal consensus. This article comprehensively surveys the recent advancements in layered metal oxide-based OER catalysts, categorized into single metal oxides, alkali cobalt oxides, perovskites, and miscellaneous metal oxides. Initially, the main OER intermediate reaction steps of layered metal oxides are scrutinized. Subsequently, the design, mechanism, and application of several pivotal layered metal oxides in the OER are systematically delineated. Finally, a summary is provided, alongside the proposal of future research trajectories and challenges encountered by layered metal oxides, with the aspiration that this paper may serve as a valuable reference for scholars in the field. [ABSTRACT FROM AUTHOR]

Constructing highly efficient electrocatalysts is vital to enhance oxygen evolution reaction (OER) performance at industrially relevant current densities. Herein, three-phase coupled Ni3S2/r-NiS/h-NiS composites are grown in situ on Ni foam (NNSN/NF) via a one-step solvothermal approach. The as-prepared composites need overpotentials of only 377 mV, 451 mV and 476 mV at 1000 mA cm−2 for the OER in alkaline freshwater, simulated seawater and seawater, respectively. In addition, the optimized catalyst exhibited long-term durability at 300 mA cm−2. Our work clarifies designing and preparing cost-effective Ni-based sulfide electrocatalysts for the OER in alkaline freshwater/simulated seawater/seawater under industrially relevant current densities. [ABSTRACT FROM AUTHOR]

Pronounced compositional regulation and microstructure evolution have a significant influence on hydrogen electrocatalysis. Herein, for the first time, we demonstrate that N,Co-codoped carbon supported Co5.47N nanoparticles (Co5.47N/N,Co-C-800) derived from a nitrogen-rich porphyrin-bridged covalent triazine polymer (CoTAPPCC) are an effective electrocatalyst for the HER in 1.0 M KOH when compared to CoCo2O4/N,Co-C-900 (pyrolysis at 900 °C) and CoO/N,Co-C-1000 (pyrolysis at 1000 °C). The structural and morphological variations of CoTAPPCC at different heat treatment temperatures were investigated through various spectroscopic techniques. We reveal that electrocatalytic HER activity is temperature- and component-dependent. The overpotentials for Co5.47N/N,Co-C-800 to reach current densities of 10 and 100 mA cm-2 were determined to be 76 and 229 mV, respectively, outperforming many other state-of-the-art HER electrocatalysts. This work also sheds light on the influence of calcination temperature on the electrocatalytic HER of final samples. [ABSTRACT FROM AUTHOR]

Active and stable electrocatalysts based on earth-abundant elements for the acidic oxygen evolution reaction (OER) are crucial for hydrogen production using proton-exchange membrane water electrolyzers. Herein, nickel-doped manganese oxide nanorods (Ni–MnO2) are prepared using a hydrothermal method in an acidic environment. The nanorods exhibit moderate stability towards the OER in 0.1 M HClO4. Doping Ni enhances OER activity, which originates from the electronic interaction that tunes the adsorption energy of OH*, which is an important OER intermediate. The most active electrode exhibits an overpotential of 390 mV to reach 10 mA cm−2 OER current density in 0.1 M HClO4. All electrodes prepared are stable towards 10 mA cm−2 galvanostatic test for at least 5 h. The dissolution of Ni and Mn species is observed, and the crystalline phase transforms to the amorphous phase under prolonged OER. [ABSTRACT FROM AUTHOR]

The hydrogen evolution reaction (HER), as a pivotal half-reaction, significantly hinders the advancement of energy conversion efficiency. Metal electrodeposition on catalysts has been demonstrated to effectively enhance the HER reactivity. Here, Ni3S2–Fe–Ni with a multilayer structure was obtained by the electrodeposition of Ni3S2 with dopants Fe/Ni, in which a number of active sites were achieved and the intrinsic conductivity of the catalyst was well improved. Elemental analyses revealed the multilayer structure consisting of Ni3S2, NiS, and Fe. The Ni3S2–Fe–Ni catalyst exhibited impressive electrochemical performance due to optimization of its structure with the overpotentials of the HER and OER of only 83 and 190 mV. Notably, at a higher current density of 100 mA cm−2, the overpotentials for the HER and OER are only 339 and 365 mV. As a bifunctional electrocatalyst, its total splitting voltage was only 1.55 V. The catalysis performance remained nearly unchanged even after 48 h of stability testing. Finally, density functional theory (DFT) calculations revealed that the potential barriers in each reaction step of the OER are evenly distributed, and optimizing the Ni3S2 structure with iron and nickel atoms reduced the reaction energy barriers during the electrochemical process, improving the OER/HER performance. [ABSTRACT FROM AUTHOR]

The development of heteroatom dual-doped porous carbon frameworks with uniform doping is highly desirable for achieving highly efficient oxygen reduction reaction (ORR) activity, due to their tunable chemical and electronic structures. Herein, porous covalent triazine-based frameworks (CTFs) incorporating nitrogen/chorine dual-doped porous carbon networks were fabricated by selecting 1,3-bis(4-cyanophenyl) imidazolium chloride as a building block, in a facile and controllable way via a bottom-up strategy. The resulting nitrogen/chorine dual-doped catalyst CCTF-700 exhibits excellent ORR performance with a more positive onset and half-wave potential (0.85 V vs. RHE), higher diffusion-limited current density and significantly improved stability in comparison with the benchmark commercial 20 wt% Pt/C catalyst. It is worth mentioning that CCTF-700 shows one of the best ORR performances among all the reported metal-free electrocatalysts under alkaline conditions. This work paves the way for a controllable and reliable strategy to craft highly efficient heteroatom dual-doped carbon catalysts for energy conversion. [ABSTRACT FROM AUTHOR]

The strategies for optimizing the morphology/structure and regulating the active sites of materials are effective ways to improve their electrocatalytic performance in the hydrogen evolution reaction (HER) and electrooxidation reaction. Herein, we demonstrate a facile strategy for constructing a NiO/NiCo2O4 porous nanowire catalyst on nickel foam (NiO/NiCo2O4/NF) as a bifunctional electrocatalyst to enhance the electrocatalytic performance for coupling the HER with the glucose oxidation reaction (GOR). Benefiting from the unique 1D porous nanowire structure and enhanced interfacial synergistic effect of the bicomponent catalyst, optimized NiO/NiCo2O4/NF-300 exhibited remarkable electrocatalytic activities for the GOR and HER with low potentials of 1.128 V and 0.212 V, respectively, at 100 mA cm−2. Moreover, the GOR exhibited a high yield of 72% for formic acid. This study provides a promising and simple strategy for the construction of 1D NiO/NiCo2O4 porous nanowire electrocatalysts with rich heterogeneous interfaces and paves a facile pathway for accelerating biomass electrochemical reaction-assisted hydrogen production. [ABSTRACT FROM AUTHOR]

Two new heteroleptic cobalt(III)dialkyldithiophosphate complex cations with a 1,2-bis(diphenylphosphino)ethane (dppe) ancillary ligand having formula [Co{S2P(OR)2}2(dppe)](B(C6H5)4) (R = –C2H5 (Co–Et); –CH(CH3)2 (Co–Pr)) have been synthesized and characterized spectroscopically as well as via single crystal X-ray diffraction analysis. The single crystal X-ray diffraction analyses reveal that the immediate geometries around Co(III) in both complexes are distorted octahedral, which are satisfied by four sulfur atoms of two dialkyldithiophosphate ligands and two phosphorus centers of the dppe ligand. These complex cations are neutralized by tetraphenyl borate B(C6H5)4 anions. The solid-state framework of both complexes are stabilized by C–H⋯π and C–H⋯C interactions. The nature of these interactions have been addressed with the help of Hirshfeld surface analysis, and percent contributions of pertinent interactions in the crystal structure of these complexes have been addressed using fingerprint plots. Both complexes have been used as heterogeneous electrocatalysts for the oxygen evolution reaction (OER). Results suggest that Co–Et is a better electrocatalyst for the OER, displaying an onset potential of 1.68 V and Tafel slope of 114 mV dec−1. Furthermore, in the homogeneous electrocatalysis of the hydrogen evolution reaction (HER) using trifluoroacetic acid, the overpotential for Co–Et and Co–Pr have been 1.05 V and 0.92 V, respectively, with turnover frequencies of 1518 s−1 and 287.5 s−1, respectively. Overall, heterogeneous OER and homogenous HER results suggest that Co–Et can be used as an efficient molecular electrocatalyst for oxygen/hydrogen evolution reactions. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the networking and interaction between N, S, and CQDs activate reactions by creating additional active sites that bind more oxygen molecules. In this study, we used nitrogen-doped graphene quantum dots as a support for Ni–Au nanoparticles and investigated the influence of different Ni–Au ratios on the N-doped graphene quantum dots as an electrocatalyst for ethanol and formate oxidation. Indeed, three electrocatalysts containing gold and nickel nanoparticles are synthesized in 1 : 1, 1 : 3, and 3 : 1 (Ni1Au1, Ni1Au3, and Ni3Au1) ratios on the nitrogen-doped graphene quantum dots as a catalyst support by the reduction process. The synthesized electrocatalysts are characterized by XRD, FESEM, and EDX methods. The electrocatalytic activity of the Ni1Au1-NGQD, Ni1Au3-NGQD, and Ni3Au1-NGQD (nickel–gold–nitrogen-doped graphene quantum dot) electrocatalysts towards ethanol and formate oxidation are evaluated in half-cell and single-fuel cell configurations. The half-cell results confirm the superiority of the Ni1Au1-NGQD electrocatalyst towards oxidation of both fuels compared to the two other electrocatalysts, and the corresponding chronoamperometry shows its high stability. Therefore, the Ni1Au1-NGQD is used as an anodic electrocatalyst in a single fuel cell configuration using ethanol and formate as fuels and hydrogen peroxide as an oxidant. The maximum power density of 8.20 and 14.23 mW cm−2 is obtained at 60 °C with 2 M ethanol and 4 M formate as the fuel in a direct ethanol–hydrogen peroxide fuel cell (DEHPFC) and direct formate–hydrogen peroxide fuel cell (DFHPFC), respectively. [ABSTRACT FROM AUTHOR]

The development of excellent bifunctional electrocatalysts is an effective way to promote the industrial application of electrolytic water. In this work, a free-standing W-doped cobalt selenide (W-CoSe300/NF) electrocatalyst with a snowflake-like structure supported on nickel foam was prepared by a hydrothermal–selenization strategy. Benefiting from the high specific surface area of the 3D snowflake-like structure and the regulation of tungsten doping on the electronic structure of the metal active center, W-CoSe300/NF shows remarkable electrocatalytic water decomposition performance. In 1.0 M KOH, the W-CoSe300/NF electrocatalyst achieved an efficient HER and OER at a current density of 50 mA cm−2 with overpotentials as low as 84 mV and 283 mV, respectively. More importantly, W-CoSe300/NF acts as both the anode and cathode of the electrolytic tank, requiring only a potential of 1.54 V to obtain 10 mA cm−2 and can operate continuously for more than 120 hours at this current density. This study proposes a new way for the design of high efficiency and affordable bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

The unsatisfactory performance of the oxygen evolution reaction (OER) and the complex preparation methods are the main challenges hindering the industrial application of OER electrocatalysts in electrochemical water splitting for hydrogen production. Herein, a convenient two-step method including electrodeposition and subsequent chemical bath deposition was utilized to synthesize a FeOOH/Ni/NiO tri-component composite on Ti mesh (TM), during which Ni(Ac)2 and FeSO4 were used as feedstocks. XRD, Raman, XPS, SEM and TEM characterizations revealed nanosheet-assembled nanospheres composed of crystalline Ni coated by amorphous NiO, and amorphous FeOOH nanosheets successively deposited on the TM surface by electrodeposition and chemical bath deposition strategies. When serving as the OER electrocatalyst, the optimized FeOOH/Ni/NiO/TM presented a superb OER performance with an overpotential of 246 mV at 50 mA cm−2, outperforming FeOOH-5/NF (321 mV), Ni/NiO/TM (348 mV) and the recently reported electrocatalysts. Additionally, its OER performance had no obvious change with only 4.3% attenuation after working for 16 h at a constant current density. The high OER performance could be assigned to the interfacial electronic engineering due to the strong coupling effect between FeOOH and Ni/NO, which increased the intrinsic activity of the active sites, modulated the adsorption of the reactant and also enhanced the stability. The simple preparation strategy, low cost and high performance endow the self-supporting FeOOH/Ni/NiO/TM with potential applications in industrial water electrolysis for hydrogen production. [ABSTRACT FROM AUTHOR]

To develop hydrogen energy production and address the issues of global warming, inexpensive, effective, and long-lasting transition metal-based electrocatalysts for the synthesis of hydrogen are crucial. Herein, a porous electrocatalyst NiMo/Ni/NF was successfully constructed by a two-step electrodeposition process, and was used in the hydrogen evolution reaction (HER) of electrocatalytic water decomposition. NiMo nanoparticles were coated on porous Ni/NF grown on nickel foam (NF), leading to a resilient porous structure with enhanced conductivity for efficient charge transfer, as well as distinctive threedimensional channels for quick electrolyte diffusion and gas release. Notably, the low overpotential (42 mV) and fast kinetics (Tafel slope of 44 mV dec-1) at a current density of 10 mA cm-2 in 1.0 M KOH solution demonstrate the excellent HER activity of the electrode, which was superior to that of recently reported non-noble metal-based catalysts. Additionally, NiMo/Ni/NF showed extraordinary catalytic durability in stability tests at a current density of 10 mA cm-2 for 70 h. The porous structure catalyst and the electrodeposition-electrocatalysis technique examined in this study offer new approaches for the advancement of the electrocatalysis field because of these benefits. [ABSTRACT FROM AUTHOR]

Transition metal phosphides (TMPs) have attracted extensive interest to catalyze the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, the development of TMPs with high conductivity is a great challenge. Herein, we report hybrids of cobalt phosphide (CoP) and copper phosphide (CuP) strongly coupled with ZIF-67 derived carbon as bifunctional ORR/OER electrocatalysts (CoP/CuP@NC). The as-prepared CoP/CuP@NC catalysts exhibit delightful activity and stability toward the ORR (E1/2 = 0.86 V) and the OER (E10 = 1.61 V). Moreover, the assembled Zn-air battery exhibits a small charge-discharge voltage gap and excellent stability. These remarkable electrocatalytic capabilities stem from the combined impact of active CoP/CuP components and the structural framework derived from ZIF-derived materials. This work provides a meaningful strategy for constructing high-performance bifunctional electrocatalysts for commercial Zn-air batteries. [ABSTRACT FROM AUTHOR]

The large-scale use of zinc–air batteries (ZABs) has been limited by their sluggish OER and ORR kinetics. The current synthesis of catalysts for air electrodes requires harsh conditions. The design and manufacture of bifunctional catalysts under mild conditions are of great significance. Herein, an electric field-induced phosphorization at room temperature is proposed to prepare bifunctional electrocatalysts designed by coupling N-doped carbon and CoP nanoparticles based on a multi-active site-integration strategy. The simple, safe, non-toxic and highly controllable electric field-induced reaction creates CoP active sites. The catalyst exhibits a remarkably narrow potential gap (ΔE) of 0.65 V between the half-wave potential of the ORR and the potential of the OER. The low ΔE signifies a superior catalytic bifunctionality of CoP@NWC. Aqueous ZABs with an optimized catalyst achieve a high discharge specific capacity of 805.8 mA h gZn−1 and long-term cycling stability over 1200 cycles. Quasi-solid-state ZABs show a discharge-specific capacity of 760.5 mA h gZn−1. The outstanding bifunctional catalytic activities originate from the synergistic effect of dual active sites between CoP and NWC induced by the electric field. This work provides a new perspective for building advanced catalysts from biomass under ambient conditions. [ABSTRACT FROM AUTHOR]

Plasma treatment as an effective strategy can simultaneously achieve surface modification and heteroatom doping. Here, an N/P-doped NiFeV oxide nanosheet catalyst (N/P-NiFeVO) constructed by Ar/PH3 plasma treatment is used to drive the oxygen evolution reaction (OER). The introduction of V species leads to the formation of an ultrathin ordered nanostructure and exposure of more active sites. Compared to the 2D NiFeV LDH, the prepared N/P-NiFeVO by plasma treatment possesses multiple-valence Fe, V and Ni species, which regulate the intrinsic electronic structure and enable a superior catalytic activity for the OER in alkaline media. Specifically, the N/P-NiFeVO only require an overpotential of 273 mV to drive the current density of 100 mA cm−2. What's more, the electrode can maintain a stable current density in a long-term oxygen evolution reaction (∼120 h) under alkaline conditions. This work provides new insight for the rational design of mixed metal oxides for OER electrocatalysts. [ABSTRACT FROM AUTHOR]

Heteroatomic anion doping represents a powerful approach for manipulating the electronic configuration of the active metal locus in electrocatalysts, resulting in enhanced multifunctional electrocatalytic properties in hydrogen/oxygen evolution reactions (HER/OER). Here, fluorine-tailored Ni2P-F3 nanosheets were synthesized and evaluated as a robust multifunctional electrocatalyst for HER, OER, and UOR. Our comprehensive experimental and theoretical investigations reveal that the anionic F effectively tailored the electronic states of the Ni2P-F3 nanosheets, resulting in an elevated d-band center and optimizing the sorption capacity of intermediates. In addition to thermodynamically and kinetically favoured redox reactions, F doping facilitates the reconstruction and generation of active γ-NiOOH. Resulting from the optimized electronic configuration and nanosheet architecture, outstanding catalytic activities are demonstrated by Ni2P-F3 with low overpotentials to reach 100 mA cm−2 for HER (177 mV) and OER (293 mV), surpassing Ni2P by 234 and 205 mV, respectively. Notably, 1.618 V is required for full-water-diversion to reach 10 mA cm−2, while 1.414 V is required with urea oxidation for 100 mA cm−2. [ABSTRACT FROM AUTHOR]

The Oxygen Evolution Reaction (OER) is crucial in various processes such as hydrogen production via water splitting. Several electrocatalysts, including metal oxides, have been evaluated to enhance the reaction efficiency. Zeolitic Imidazolate Framework-67 (ZIF-67) has been employed as a precursor to produce Co3O4, showing high OER activity. Additionally, the formation of composites with carbon-based materials improves the activity of these materials. Thus, this work focuses on synthesizing ZIF-67 and commercial activated carbon (AC) composites, which were used as precursors to obtain Co3O4/C electrocatalysts by calculating ZIF-67/CX (X = 10, 30, and 50, the mass percentage of AC). The obtained materials were thoroughly characterized by employing X-ray powder diffraction (XRD), confirming the cobalt oxide structure with a sphere-like morphology as observed in the TEM images. The presence of oxygen vacancies was confirmed by infrared spectroscopy and EPR measurements. The electrocatalytic performance in the OER was investigated by linear sweep voltammetry (LSV), which revealed an overpotential of 325 mV at 10 mA cm−2 and a Tafel slope value of 65.32 mV dec−1 for Co3O4/C10, superior in activity to several previously reported studies in the literature and electrochemical stability of up to 8 hours. The reduced value of charge transfer resistance, high double-layer capacitance, and the presence of Co3+ ions justify the superior performance of the Co3O4/C10 electrocatalyst. [ABSTRACT FROM AUTHOR]

Interface engineering for the controllable preparation of highly efficient electrocatalysts is still a great challenge in the development of inexhaustible energy supplying systems. Herein, the successful synthesis of P-CoMoO4/CF nanoarray electrocatalysts with different morphologies through facile hydrothermal synthesis, immersion and annealing strategies is reported. The nanotube array electrode of P-CoMoO4/CF-1 with abundant interfacial active sites presented exceptional activity for overall water splitting, approaching 100 mA cm−2 at a low voltage of 1.6 V. In addition, the electrodes exhibit good stability in long-term reactions, showing good potential for hydrogen and oxygen production at constant voltage for more than 24 hours. The present work indicates that MOF decoration of arrays with unique surfaces based on interfacial engineering is an advisable strategy to simultaneously improve interfacial reaction dynamics and catalyst activity, paving the way for designing other arrays as versatile electrodes combining the advantages of POMs and MOFs. [ABSTRACT FROM AUTHOR]

In contrast to the energy-consuming Haber–Bosch process, ammonia synthesis by electrocatalysis under ambient conditions is an efficient and environmentally friendly method. In this work, through first principles calculations, the potential of four dual-atom FeTM (TM = Fe, Mo, Co, and V) anchored graphyne (FeTM@GY) as efficient nitrogen reduction reaction (NRR) catalysts is systematically investigated. Among them, FeMo@GY is the most promising, with excellent NRR catalytic activity, high ability to suppress the competing hydrogen evolution reaction (HER), and good stability. Moreover, NRR prefers the maximum pathway with the calculated onset potentials of −0.27 V for FeMo@GY. This work not only suggests that FeMo@GY holds great promise as an efficient, low-cost, and stable dual-atom catalyst for NRR but also further provides a guiding idea for the design of efficient NRR catalysts. [ABSTRACT FROM AUTHOR]

The development of high-performance and highly stable electrocatalysts is crucial and challenging for the hydrogen evolution reaction (HER). MOFs complexed with SnS2 can form complexes with inserted structures, and their large specific surface area and numerous pores favor mass transfer, exposing the S active sites to more SnS2, improving the utilisation of the active sites and enhancing the catalytic activity for the HER. Structural collapse can be hindered to improve the stability of the HER composites. Herein, six different kinds of SnS2 were synthesized by a hydrothermal method under discrete conditions, and SI8-SnS2 was screened out to have optimal morphology and electrocatalytic performance. Two innovative SnS2@Ni-MOF and SnS2@HKUST-1 as efficient electrocatalysts were synthesized by a facile grinding method for hydrogen generation. SnS2@Ni-MOF and SnS2@HKUST-1 catalysts showed lower overpotentials of 117 mV and 142 mV at 10 mA cm−2 (η10) and smaller Tafel slopes (58 mV dec−1 and 93 mV dec−1) than six different kinds of SnS2, Ni-MOF and HKUST-1 in 0.5 M H2SO4. Meanwhile, the Cdl values for SnS2@Ni-MOF and SnS2@HKUST-1 were estimated to be 11.5 mF cm−2 and 8.0 mF cm−2, and the stabilities of SnS2, Ni-MOF, HKUST-1, SnS2@Ni-MOF, and SnS2@HKUST-1 were tested at a current density of 10 mA cm−2. The current densities of SnS2@Ni-MOF and SnS2@HKUST-1 were stable over 8 h compared to the pure samples, and SEM, XPS tests were run after the HER test, indicating that the materials have excellent electrocatalytic stability. The syntheses of SnS2@Ni-MOF and SnS2@HKUST-1 enhance their intrinsic catalytic activity, and the porous structure promotes mass transfer efficiency, thereby improving the HER performance, which will guide the development of new and promising electrocatalysts for HER. [ABSTRACT FROM AUTHOR]

Developing high performance noble-metal-free electrocatalysts as an alternative to Pt-based catalysts for the oxygen reduction reaction (ORR) in energy conversion devices is highly desirable. We report herein the preparation of a coordination-polymer (CP)-derived Fe/CP/C composite as an electrocatalyst for the ORR with excellent activity and stability both in solution and in Zn-air batteries. The Fe/CP/C catalyst was obtained from the pyrolysis of an iron porphyrin Fe(TPP)Cl (5,10,15,20-tetraphenyl-21H, 23H-porphyrin iron(III) chloride) grafted Zn-coordination polymer with dangling functional groups 4,4'-oxybisbenzoic acid and 4,4'-bipyridine ligands. The Fe/CP/C catalyst showed much higher ORR activity with a half-wave potential (E1/2) of 0.90 V (vs. RHE) than the Fe/C catalyst (E1/2 = 0.85 V) derived from the carbon-blacksupported Fe porphyrins in 0.1 M KOH solution. When Fe/CP/C was used as the cathode electrocatalyst in Zn-air batteries (ZABs), the ZABs achieved a significantly higher open circuit voltage (OCV = 1.43 V) and maximum power density (Pmax = 142.8 mW cm-2) compared with Fe/C (OCV = 1.38 V, Pmax = 104.5 mW cm-2) and commercial 20 wt% Pt/C (OCV = 1.41 V, Pmax = 117.6 mW cm-2). Using dangling functional groups in CP to increase the loading efficiency of iron porphyrins offered a facile method to prepare high-performance noble-metal-free electrocatalysts for the ORR, which may provide promising applications to energy conversion devices. [ABSTRACT FROM AUTHOR]

A 3D hierarchical nickel--iron hexacyanoferrate electrocatalyst was successfully grown on nickel foam using an energy-efficient in situ self-assembly method. The as-prepared NiFeHCF@NF electrode has good morphology and intimate contact with the NF compared to electrodes from the co-precipitation method. The well-designed NiFeHCF@NF nanostructure delivers prominent performances that require overpotentials as low as 210 and 125 mV@10 mA cm-2 for the OER and HER in 1 M KOH, respectively. Tafel slope and electrochemical impedance studies further revealed favourable kinetics during electrolysis. Hence, an NiFeHCF@NF--NiFeHCF@NF water electrolyser only required 1.56 V@10 mA cm-2 with an ~2.5% potential loss. Furthermore, the synergistic effect of iron and nickel with ferrocyanide improved the structural stability and promoted the generation of active phases during the OER/HER, resulting in outstanding durability for 150 h. Moreover, the novel all-in-one strategy can be used to explore other bifunctional and cost-efficient electrocatalysts for various applications. The solar-based water electrolysis and environmental assessment confirmed the practical use of NiFeHCF@NF for eco-friendly industrial hydrogen production. [ABSTRACT FROM AUTHOR]

The exploration of highly efficient noble-metal-free catalysts for overall water splitting is crucial for industrial application. In this study, FeS nanosheets/1T-MoS2 nanoflowers on conductive iron foam (IF) were prepared as efficient electrocatalysts for the HER and OER using a solvothermal method. The prepared FMS0.5 electrocatalyst can deliver a high current density of 100 mA cm−2 at low overpotential potentials of 245 and 316 mV and small Tafel slopes of 80.6 and 88.3 mV dec−1 for the HER and OER. The FMS0.5//FMS0.5 exhibited a low voltage of 1.56 V at 10 mA cm−2 with remarkable stability for 40 h in alkaline water. Benefiting from the 3D morphology and interface coupling interactions between the FeS nanosheets and 1T-MoS2 nanoflowers, the self-supporting electrocatalyst could tune the charge/ion transfer path and electronic structure to facilitate the HER and OER activity. Hence, this study would provide new ideas for exploiting highly active non-noble-metal bifunctional catalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

Due to the slow kinetics and large overpotential of the oxygen evolution reaction (OER) in electrochemical water splitting, it is important to develop efficient and low-cost electrocatalysts for the OER. In this work, we used Co-PBA as the substrate, and induced the growth of NiFe-LDH on the surface of cubic Co-PBA by the hydrothermal method. The Co-PBA@NiFe-LDH electrocatalysts with a flower-like morphology and heterostructures were finally utilized to evaluate the OER performance. The results reveal that during the OER process, the flower-like structure allows Co-PBA@NiFe-LDH-30 to expose more active centers, and increases the contact area between the electrolyte and active sites. Meanwhile, benefiting from the synergistic effect of multi-metals and the heterostructure, Co-PBA@NiFe-LDH-30 demonstrated remarkable electrochemical performance with a lower overpotential of 253 mV at 10 mA cm−2 and a smaller Tafel slope of 54 mV dec−1. This design strategy provides a promising approach for the development of OER electrocatalysts in the future. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal sulfides possess high intrinsic catalytic activity for the oxygen evolution reaction (OER) during water splitting but are restricted by their low conductivity and unattractive stability in alkaline electrolytes. Herein, newly designed CoS2/MoS2 nanosheets with enriched heterointerfaces synthesized by the combination of hydrothermal and vulcanization methods showed great promise as a highly efficient OER electrocatalyst. Owing to the fast vulcanization process, some heterometallic sulfide nanoparticles get distributed on the nanosheets, thus forming a nanoparticle-nanosheet bridging structure. The rich heterogeneous interface between CoS2 and MoS2 regulates the electronic structure and provides sufficient electrochemical active sites, thus forming a fast channel conducive to electron transport and ensuring high OER activity. Besides, the rough heterostructured surface enhances hydrophilicity, which promotes the decomposition of H2O and decreases the energy barrier of intermediate reactions, leading to fast electrochemical kinetics. Benefiting from the structural merits, the optimized CoS2/MoS2-1 : 1 nanosheets exhibit a low overpotential of 283 mV at 10 mA cm−2, a small Tafel slope of 105.32 mV dec−1 and long-term durability for the OER. [ABSTRACT FROM AUTHOR]

Cellulose nanofiber (CNF) is an environmentally friendly material with a high specific surface area, which is an ideal candidate for cathode catalysts in zinc–air batteries (ZABs). However, untreated CNF-based carbon materials suffer from low intrinsic activity and fewer micro-mesopores. Herein, we developed an N-doped porous carbon aerogel from CNF and graphite phase carbon nitride (g-C3N4) via hydrothermal pretreatment and the carbonization process. The CNF can serve as the skeleton of the aerogel that leads to an interconnected porous structure, while g-C3N4 guarantees the in situ N doping and the formation of more nanopores. Therefore, the as-prepared carbon aerogel exhibits excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances owing to the successful N doping with sufficient graphite-N and pyridine-N active sites (69.1%) and high specific surface areas (785.4 m2 g−1). The assembled ZABs with a carbon aerogel deliver a specific capacity of 790 mA h g−1 and an energy density of 945.6 W h kg−1 with a long-term stability over 100 h. This work opens a new avenue for the effective conversion of abundant biomass into bifunctional air cathodes for energy-related applications. [ABSTRACT FROM AUTHOR]

Medium entropy alloys, consisting of four elements in close to isotropic proportions, have attracted a great deal of attention because of their unique properties (excellent strength, corrosion resistance, etc.). Here, we present a series of quaternary medium entropy alloy FeCoNiW electrocatalysts loaded onto nitrogen-doped carbon (NC) skeletons. The prepared medium entropy alloy catalysts have excellent OER catalytic activity and stability. In alkaline media, the FeCoNiW-NC electrocatalysts annealed at 350 °C were able to achieve an overpotential as low as 225 mV at a current density of 10 mA cm−2, which is 55 mV lower than that of the commercial RuO2, while it has a smaller Tafel slope of 54 mV dec−1. The introduction of W leads to a change in the electronic structure of the FeCoNi alloy and increases the specific surface area of the catalyst, exhibiting excellent performance. This work contributes to the exploration of OER catalysts by opening new avenues for the design of efficient and economical OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The electrocatalytic carbon dioxide reduction reaction (CO2RR) is considered as a promising approach for simultaneous CO2 treatment and production of value-added chemicals. Bismuth has been demonstrated as a fascinating electrocatalyst for selective conversion of CO2 to HCOOH. In this study, we comprehensively investigated the effects of size, morphology, and carbon supports on the CO2RR performance of Bi catalysts to enhance their electrocatalytic CO2RR activity and HCOOH selectivity. Specifically, Bi nanospheres with varying sizes were synthesized by adjusting the amount of polyvinylpyrrolidone (PVP), achieving similar selectivity for HCOOH but increasing current density with decreasing size. Bi nanoplates and Bi nanoflowers were also prepared through the reduction of BiOCl precursors, with Bi nanoflowers demonstrating a superior morphology compared to other Bi nanocrystals while achieving a HCOOH faradaic efficiency (FEHCOOH) of 95% at −1.6 V vs. SCE and excellent durability over 12 hours. The predominance of *HCOO intermediates in the in situ ATR-SEIRA spectra indicates that during the CO2RR, Bi nanoflowers primarily followed the pathway leading to HCOOH production. Furthermore, incorporation of Ketjenblack into the synthesis process resulted in carbon-supported Bi catalysts, which exhibited approximately 20% enhancement in FEHCOOH within a wide potential range from −1.3 V to −1.8 V vs. SCE due to an improved separation effect and electron transfer capacity provided by carbon materials. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) electrocatalysts are frequently made from noble metal-based oxides like ruthenium/iridium oxides. However, because of their scarcity and high price, researchers are now focusing on creating innovative OER catalysts based on affordable transition metals that have improved electrical conductivity and accessibility to active sites. Metal–organic frameworks (MOFs), a unique class of inorganic materials with excellent physical and chemical properties, have witnessed significant progress in promising green energy systems. In this work, a novel mixed-ligand metal–organic framework [Co(μ-1κN,2κN′-BDP)(μ3-1κoo′,2κo′′2κo′′′-BTC)]n·nH2O (BDP = boron-dipyrromethene or BODIPY; BTC = benzene tricarboxylate) denoted as CoBDPMOF has been synthesized, and its composites with different carbon materials have been designed. Compared to the pristine MOF, the composites showed enhanced electrocatalytic activity toward the oxygen evolution reaction (OER) in alkaline media. In addition, the CoBDPMOF with activated carbon showed the highest OER performance with a low Tafel slope (82 mV dec−1) and the highest j600 (59.8 mA cm−2), outperforming noble metal IrO2, the OER benchmark electrocatalyst. This study presents new insights into the design and application of CoBDPMOF-based materials for energy conversion and suggests promising avenues for further research and development in electrocatalysis. [ABSTRACT FROM AUTHOR]

Carbon dots with good photoelectric properties are usually used as photocatalysts and electrocatalysts, but the good catalytic performance of carbon dots as nanomaterials for thermal catalysis is ignored. Herein, the application of novel efficient catalysts based on carbon dots for the transformation of carbon dioxide (CO2) to carbonates under solvent-free conditions is described. Carbon dots containing carboxyl, hydroxyl, and amine groups were prepared by a microwave technique and employed together with KI, which showed exceptional catalytic activity in the cycloaddition of carbon dioxide with different epoxides. In addition, the catalyst was easily reusable and had stable recyclability. And the catalyst displayed outstanding catalytic performance due to the synergistic effect of carboxyl (–COOH), hydroxyl (–OH), and amine (–NH) groups. [ABSTRACT FROM AUTHOR]

Exploring bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which combine the features of effective electrocatalytic activity, high electrical conductivity, and superior stability, remains a significant challenge for rechargeable Zn–air batteries (ZABs). Herein, we report a material, selenium (Se)-doped CoSe2 embedded in carbon nanofibers (CNFs) (denoted as Se–CoSe2/CNFs), which was synthesized as a bifunctional electrocatalyst for ZABs via electrospinning combined with in situ growth of Zeolitic Imidazolate Framework-67 strategy, followed by carbonization and a facile selenization process. The as-synthesized Se–CoSe2/CNF electrode exhibits satisfactory electrochemical performance in an alkaline environment with a low overpotential of 325 mV at 10 mA cm−2 toward OER and a half-wave potential of 0.80 V for ORR. Remarkably, the Se–CoSe2/CNF catalyst-based ZAB shows a peak power density of 149.4 mW cm−2 and the voltage window barely changes after 180 h of cycling at 5 mA cm−2, which proves its great potential application for advanced bifunctional electrocatalysis in ZABs. [ABSTRACT FROM AUTHOR]

The utilization of two-dimensional (2D) nanosheets as catalysts is promising due to their atomic-scale thickness and extensive surfaces. The development of a high-quality, flexible Pt-based nanosheet with an efficient synthesis method is imperative. In this study, we present a 2D Pt2Pd porous alloy nanosheet synthesized through a novel process involving molten-alkali mechanochemical and borane morpholine complex reduction methods. This nanosheet exhibits a pristine 2D active surface, serving as an efficient catalyst for the oxygen reduction reaction (ORR). The Pt2Pd porous alloy nanosheet catalyst displays a high half-wave potential of 0.956 V versus the reversible hydrogen electrode (RHE), along with remarkable mass and specific activities of 1.38 A mg−1Pt and 3.70 mA cm−2 (at 0.9 V versus the RHE). When applied as the cathode in a zinc–air battery, it achieves a power density of 0.31 W cm−2 and demonstrates outstanding durability. This research introduces an innovative strategy for advancing high-quality, flexible 2D Pt-based materials. [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]

Deliberate engineering of built-in electric fields (BEFs) can facilitate electron transfer and promote asymmetrical charge distribution, thereby regulating the adsorption/desorption of reaction intermediates. Herein, an oxygen-deficiency-rich MnO-CeO2 is synthetized supported on a carbon sphere (MnO-CeO2@Cs), adeptly crafted with a prominent work function difference (ΔΦ) and robust BEF, targeting the electrocatalytic oxygen reduction reaction (ORR). Empirical and theoretical results substantiate that the BEF triggers interfacial charge redistribution, fine-tuning the adsorption energy of oxygen intermediates and hastening reaction kinetics. Consequently, the MnO-CeO2@Cs showcases commendable performance (E1/2 = 0.80 V and jL = 5.5 mA cm−2), outshining its single-component counterparts. Impressively, the MnO-CeO2@Cs-based zinc–air batteries (ZABs) boast an exemplary power density of 202.7 mW cm−2 and enduring stability of 297 h. Additionally, the solid-state ZAB commands a peak power density of 67.4 mW cm−2, underscoring its potential in flexible ZAB applications. This work delineates a strategic avenue to harness interfacial charge redistribution, aiming to enhance the catalytic performance and longevity of energy conversion/storage apparatuses. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) can be coupled with renewable energy power generation technology and is considered to be a highly promising hydrogen production technology. However, the acidic electrolyte environment, as well as the numerous sulfonic acid groups on the proton exchange membrane surface, can seriously corrode the oxygen evolution reaction (OER) catalyst and even cause deactivation. To develop an efficient acidic OER catalyst, the IrOx/WO3 heterostructure OER catalyst was prepared by a hydrothermal-calcination method. The coordination environment of IrOx was regulated through the electronic rearrangement effect, improving the OER activity and stability of the catalyst in acidic media. The prepared IrOx/WO3 exhibits excellent OER activity in 0.5 M H2SO4, with an overpotential of only 260 mV to achieve a current density of 10 mA cm−2 and a mass activity of 176.8 A gIr−1. It can stably operate for over 12 hours at a current density of j = 10 mA cm−2. [ABSTRACT FROM AUTHOR]

Developing efficient and economical catalysts is essential for water splitting. The application of MOF catalysts in water splitting is limited by poor conductivity; however, the introduction of conductive TMS could enhance their activity. Herein, novel composite Fe9S10/Fe-MOF/NF-2 was constructed by introducing dendritic Fe9S10 onto the surface of a 2D ultrathin Fe-MOF. Composite catalysts elaborately utilize the structural and chemical advantages of MOF and TMS while improving the deficiencies of monomers through the combination. Owing to the optimal structure, the hybrid catalyst Fe9S10/Fe-MOF/NF-2 displayed better catalytic performance than bare Fe-MOFs and Fe9S10, with low overpotentials of 202 and 216 mV at 10 mA cm−2 in alkaline solution and simulated seawater, respectively. This work provides an innovative approach to modify MOFs as electrocatalysts for OER. [ABSTRACT FROM AUTHOR]

The rational design of earth-abundant and efficient electrocatalysts to replace precious metal-based materials is highly anticipated for overall water splitting. Herein, NiCo2O4 electrocatalysts with different Fe doping amounts (Fex-NCO, x = 1, 2, 3) were synthesized by a low-temperature chemical method. It was interesting to find that the doping of Fe induced the formation of NiCo2O4 nanotube arrays by modulating the Fe content. The Fe3-NCO electrode with a nanotube structure and rich oxygen vacancies exhibited exceptional electrocatalytic activities for the hydrogen evolution reaction (97 mV, 10 mA cm−2) and oxygen evolution reaction (188.4 mV, 10 mA cm−2). DFT calculations revealed that Fe promoted the modulation of the electronic structure, which played a crucial role in optimizing the reaction intermediates and altered the energy level of the d band center, and as a result, enhanced the water dissociation ability. Additionally, a low cell voltage of 1.56 V (10 mA cm−2) was realized for water splitting based on an as-fabricated Fe-doped NiCo2O4 nanotube array bifunctional electrode. [ABSTRACT FROM AUTHOR]

The rational modification of electronic structures to create catalytically active sites has been proved to be a promising strategy to efficiently facilitate the urea oxidation reaction (UOR). Herein, a well-defined nanosheet arrays catalyst of Ni(OH)2 doped with dual cations of Co and Mn on Ni foam (NF) (Co/Mn–Ni(OH)2) is synthesized through a simple hydrothermal process. Benefiting from the advantages of unique structures and modified binding strengths, it is found experimentally that the obtained Co/Mn–Ni(OH)2 catalyst only requires a potential of 1.38 V to deliver a current density of 100 mA cm−2 and exhibits a small Tafel slope of 35 mV dec−1, outperforming single-component-incorporated Ni(OH)2. Moreover, the catalyst has shown excellent stability for 25 h at a current density of 50 mA cm−2. Additionally, first-principles calculations demonstrate that the co-incorporation of Co and Mn remarkably lowers the adsorption barrier of CO(NH2)2* on the catalyst surface, and accelerates the dissociation of the CO(NH2)2* intermediate into CO* and NH* intermediates, which synergistically improve the UOR reaction kinetics. This work provides a generic paradigm for designing advanced and effective catalysts toward the UOR. [ABSTRACT FROM AUTHOR]

The development of low-cost earth-abundant electrocatalysts to produce ammonia (NH3) with high efficiency for the nitrogen (N2) reduction reaction (NRR) remains challenging. Herein, we propose the development of highly efficient ultrathin nitrogen-vacancy-rich molybdenum nitride nanosheets (MoN-NV) for NRR using basic electrolytes under ambient conditions. In 0.1 M KOH, this catalyst attained a high faradaic efficiency (FE) of ∼14% with an NH3 yield of 22.5 μg h−1 mg−1cat at −0.3 V vs. a reversible hydrogen electrode under ambient conditions. The characterization results and electrochemical studies disclosed that nitrogen vacancies in the MoN-NV nanosheets played a critical role in the enhanced electrocatalytic activity for NRR. Furthermore, the recycling tests confirmed the stability of the catalyst during NRR electrolysis. [ABSTRACT FROM AUTHOR]

The electrocatalytic splitting of water to produce hydrogen is regarded as an efficient and promising strategy but is limited by its large overpotential; thus, a highly efficient electrocatalyst is urgently needed. Mixed metal doping is an important strategy in defect engineering because the heteroatoms can change the intrinsic structure to form defects by affecting the atomic coordination mode and adjusting the electronic structure, which is often accompanied by morphological changes. Herein, two-dimensional layered bimetallic Co–pydc containing axially coordinated water molecules was selected by producing surface defects through Fe doping in Co centers as bifunctional electrocatalysts for OER and HER. The optimized Co0.59Fe0.41–pydc possesses outstanding OER performance with the lowest overpotential of 262 mV to reach j = 10 mA cm−2, and Co0.75Fe0.25–pydc possesses superior HER performance with the lowest overpotential of 96 mV at j = 10 mA cm−2. Furthermore, the overall water splitting device assembled with Co0.59Fe0.41–pydc@NF//Co0.59Fe0.41–pydc@NF affords a current density of 10 mA cm−2 at only 1.687 V. This work emphasizes the surface defects formed by tuning the electronic structure of metal centres accompanied with morphological changes of bimetallic dopants for efficient overall water splitting. [ABSTRACT FROM AUTHOR]

The development of high-efficiency, precious-metal-free electrical catalysts for hydrogen evolution reactions is expected to facilitate the production of hydrolytic hydrogen fuels. Heterogeneous structures with a one-dimensional (1D) morphology exhibit efficient electrocatalytic effects owing to their abundance of active centers in the radial direction and convenient axial charge transfer in interconnected networks. Hence, a 1D MoS2/NiCoP heterogeneous junction for highly efficient hydrogen evolution performance was developed. As expected, the optimized MoS2/NiCoP/NF showed a low overpotential of 148 mV for hydrogen evolution with a current density of 10 mA cm−2 in 1.0 M KOH. Meanwhile, the developed heterogeneous structure exhibited high stability within 50 hours of continuous testing. [ABSTRACT FROM AUTHOR]

In this work, M@Pd/N (M = cobalt, nickel; N = multi-walled carbon nanotube, reduced graphene oxide) anodic electrocatalysts are synthesized and studied for formate oxidation, and used directly in formate-hydrogen peroxide fuel cells (DFHPFCs) for the first time. The effect of core materials (M = cobalt, nickel) on the activity of M@Pd/MWCNTs for formate oxidation has been studied. For this purpose, a Co@Pd/MWCNT electrocatalyst is synthesized using a two-step reduction method. Comparing the electrochemical surface area (ECSA), the formate oxidation current density (Ip) and onset potential of formate oxidation (Eons) values of Co@Pd/MWCNTs and Ni@Pd/MWCNTs showed that the presence of Ni in the core instead of Co improved the catalytic performance of the M@Pd/MWCNT catalyst due to the synergistic effects between Ni and Pd. The ECSA and Ip values of the Ni@Pd/MWCNTs are 1.01 and 1.78 times higher than those of Co@Pd/MWCNTs. After optimizing the core material, in the next step, the effect of the catalyst support on the performance of Ni@Pd nanoparticles is evaluated. Comparing the ECSA, Ip and Eons values of Ni@Pd/MWCNTs and Ni@Pd/rGO showed that Ni@Pd/rGO performs better for formate oxidation because of the high surface area and conductivity of rGO compared to MWCNTs. The ECSA and Ip values of Ni@Pd/rGO are 1.09 and 1.57 times higher than those on Ni@Pd/MWCNTs. Finally, the effect of these electrocatalysts in DFHPFC is evaluated and the results are in good agreement with the three electrode results. The maximum power density of the Co@Pd/MWCNTs, Ni@Pd/MWCNTs and Ni@Pd/rGO is 49.90, 62.29 and 107.29 mW cm−2, respectively. [ABSTRACT FROM AUTHOR]

Herein, novel and efficient IF-supported NiCu (NiCu/IF) and NiMn (NiMn/IF) electrocatalysts are successfully deposited on iron foam (IF) via electrolysis of spent cupronickel (SCN), with outstanding performance for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in an alkaline solution, respectively. The physical and electrochemical characterization results demonstrate that the catalysts possess a large active surface area, remarkable performance, and excellent durability. [ABSTRACT FROM AUTHOR]

Owing to the clean and environment friendly advantages, electrochemical water splitting stands out among various hydrogen production strategies. Electrocatalysts play an important role in the hydrogen evolution reaction (HER). Hence, Pt-(Ni0.5Co0.5)2P/S-carbon fibers as electrocatalysts for highly efficient HER were prepared through the structural designing of CNF and heteroatom doping (sulfur (S) or boron (B)). First, three composites of the (Ni0.5Co0.5)2P/carbon fiber ((Ni0.5Co0.5)2P/CNF), (Ni0.5Co0.5)2P/porous carbon fiber ((Ni0.5Co0.5)2P/PCNF), and (Ni0.5Co0.5)2P/hollow porous carbon fiber ((Ni0.5Co0.5)2P/HPCNF) were fabricated via a facile electrospinning with a solvothermal method. (Ni0.5Co0.5)2P/PCNFs showed the smallest overpotential at a current density of 10 mA cm−2 among the three structures. (Ni0.5Co0.5)2P nanosheets loaded on the porous CNF with a large active surface area may expose active sites and shorten the ion transport channel. To improve the catalytic performance of (Ni0.5Co0.5)2P/PCNF, Pt nanoparticles were anchored on (Ni0.5Co0.5)2P/heteroatom doped-PCNF by the chemical reduction method. Pt-(Ni0.5Co0.5)2P/S doped-PCNF exhibited a small overpotential of 64 mV for the HER with 74.9 mV dec−1 Tafel slope and a good stability, which was attributed to the conductive S-doped PCNF facilitating electron transport, accompanying the synergistic effect between the bimetallic phosphide and Pt nanoparticles, thus providing a facile method for an efficient HER electrocatalysis. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials (CNMs, carbon dots, carbon nanotubes, and graphene) have received much attention in recent decades for their technological roles as electrocatalysts for biosensing and fuel cell applications in aqueous solutions. Their complex form factor presents challenges for delineating structure–property relationships, namely the interplay of electroactive area surface defects and exposed graphene planar structure, for optimizing their electrocatalytic activity. Conflicting examples in the literature show higher defect density in the graphene structure with increased or decreased conduction of the material. The graphenyl sheet curvature, voltage range of the electrochemical redox reaction, dispersion of charged impurities affecting the charge mobility, and overall resistivity of the CNM materials should be considered to optimize the overall electrochemical activity, particularly as they relate to redox reactions taking place in the −0.2 to +0.3 V standard potential range. [ABSTRACT FROM AUTHOR]

Under the gravity of future socio-economic development, the viability of water electrolysis still hinges on the accessibility of stable earth-abundant electrocatalysts and net energy efficiency. This work emphasizes the design and synthesis of two newly developed cobalt(II) complexes, [Co(HL)2(NCS)2] (Comono) and [Co2(L)3(CH3OH)]ClO4 (Codi), with a (N,O)-donor ligand, HL (2-methoxy-6-(((2-methoxyphenyl)imino)methyl)phenol). The study delves into understanding their structural, morphological, magnetic, and charge transport characteristics. Moreover, the study explores the potential of these complexes in catalyzing hydrogen production through heterogeneous electrocatalysis. The X-ray crystal structure of Comono reveals the octahedral geometry of the Co(II) ion, adopting two HL units and two NCS− units. The Codi complex exhibits a doubly-phenoxo-O-bridged (μ1,1) dinuclear complex, forming a typical octahedral geometry for both the Co(II) centres in coupling with three units of L−. Temperature-dependent magnetic susceptibility measurements showed that all of the Co(II) ion in Comono shows a typical paramagnetic behaviour for high spin octahedral Co(II) ions while the Co(II) centres in Codi are coupled with doubly-phenoxo-bridges bearing weak ferromagnetic characteristics at low temperature. Electron transport properties of the Co(II) complex-mediated Schottky device address the superior carrier mobility (μ) for Codi (9.21 × 10−5) over Comono (2.02 × 10−5 m2 v−1 s−1) with respective transit times of 1.70 × 10−9 and 7.77 × 10−9 s. Additionally, electron impedance spectral analysis supports the lower electrical transport resistance of Codi relative to Comono. The heterogeneous electrocatalytic HER activity of Codi and Comono in 0.1 M KOH shows excellent electrocatalytic efficiency in terms of the various electrochemical parameters. Constant potential electrolysis, multi-cycle CVs, and post-HER analysis reveal the pre-catalytic nature of the complexes, which in turn delivers Co3O4 nanoparticles as the active catalysts for efficient hydrogen evolution. [ABSTRACT FROM AUTHOR]

Electrocatalytic carbon dioxide (CO2) reduction to valuable chemical compounds is a sustainable technology with enormous potential to facilitate carbon neutrality by transforming intermittent energy sources into stable fuels. Among various electrocatalysts, metal--organic frameworks (MOFs) have garnered increasing attention for the electrochemical CO2 reduction reaction (CO2RR) owing to their structural diversity, large surface area, high porosity and tunable chemical properties. Ligands play a vital role in MOFs, which can regulate the electronic structure and chemical environment of metal centers of MOFs, thereby influencing the activity and selectivity of products. This feature article discusses the strategies for the rational design of ligands and their impact on the CO2RR performance of MOFs to establish a structure--performance relationship. Finally, critical challenges and potential opportunities for MOFs with different ligand types in the CO2RR are mentioned with the aim to inspire the targeted design of advanced MOF catalysts in the future to achieve efficient electrocatalytic CO2 conversion. [ABSTRACT FROM AUTHOR]