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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]

In recent years, as a green renewable energy production technology, electrochemical water splitting has demonstrated high development potential. Many materials have been reported as successful catalysts in the water-splitting field. However, it is still a huge challenge to produce bifunctional electrocatalysts for the efficient and sustainable generation of hydrogen and oxygen simultaneously. Herein, we successfully developed oxygen vacancies abundant CuCo layered double oxide (Ov-CuCo-LDO) hollow nanotube arrays (HNTAs) loaded on nickel foam as advanced electrocatalysts for total water splitting. When the current density was 10 mA cm−2, the Ov-CuCo-LDO HNTAs exhibited outstanding onset overpotentials of 53.9 and 72.5 mV for the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline medium, respectively, because of the bimetallic synergistic effect between the cobalt and copper and the unique hollow porous structure. In addition, an as-assembled Ov-CuCo-LDO‖‖Ov-CuCo-LDO electrolytic cell showed a small potential of 1.55 V to deliver a current density of 10 mA cm−2. Moreover, it also showed remarkable durability after long-term overall water splitting for more than 20 h. The research results in this paper are of great interest to practical applications of the water decomposition process, providing clear and in-depth insights into preliminary robust and efficient multifunctional electrocatalysts for overall water splitting. [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]

Due to the slow reaction kinetics of the oxygen evolution reaction (OER), the electrolysis rate of water is greatly limited. Therefore, it is of great significance to study stable and efficient non-noble metal based electrocatalysts. In this paper, three-dimensional (3D) spherical V-NiFe LDH@Ni3S2 was developed by exquisitely decorating ultra-thin V-doped NiFe layered dihydroxide (NiFe-LDH) on Ni3S2 nanosheets supported by nickel foam (NF). It is worth mentioning that V-NiFe LDH@Ni3S2 exhibits an excellent electrocatalytic performance and only 178 mV overpotential is required in 1 M KOH to achieve a current density of 10 mA cm−2. Long-term chronoamperometry manifests its superior electrochemical stability. The combination of NiFe LDH and conductive substrate coupling can drastically afford abundant active sites and accelerate charge transfer, and V doping can markedly regulate the electronic structure. Therefore, the activity and durability of the electrocatalysts are greatly improved. This study may provide a new strategy for the preparation of efficient OER electrocatalysts. [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 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]

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]

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]

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]

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]

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]

It is highly desirable for porous coordination polymers (PCPs), including metal–organic frameworks (MOFs) and Prussian blue analogues (PBAs), to retain their intrinsic characteristics in electrocatalysis, instead of being used as precursors or templates for further total conversion to other compounds via high-temperature calcination. Here, a S-treated two-dimensional (2D) CoFe bimetallic PBA grown on carbon fiber paper (CFP) (named S-CoFe-PBA/CFP) is assembled and applied as a highly efficient oxygen evolution reaction (OER) electrocatalyst in 1 M KOH. The resultant S-CoFe-PBA/CFP demonstrates significantly improved OER catalytic activity; overpotentials of only 235, 259, and 272 mV are needed to drive current densities of 10, 50, and 100 mA cm−2, respectively, with a super low Tafel slope of 35.2 mV dec−1. Even more noteworthy, a current density of 90 mA cm−2 can be achieved when a potential of 1.5 V vs. RHE is applied, which is 6.4 times higher than that of commercial Ir/C in the same environment. The outstanding electrocatalytic performance can be ascribed to two reasons caused by the S-treatment process. On one hand, H+ from intermediates of *OH and *OOH can be captured by –SOx distributed on the surface of the catalyst, thus accelerating the breaking of O–H; on the other hand, partial phase transformation of CoFe-PBA leads to the in situ formation of amorphous CoSx nanogauze on the surface, and the resultant electronic interactions between the two phases contribute much to the improvement of charge transfer and adsorption for OER intermediates. This work provides a new avenue for the design of highly efficient PCP-based OER electrocatalysts. [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]

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 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 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 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]

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]

A self-derivation strategy using conductive substrates is used to prepare one-piece highly efficient bifunctional electrodes, where the chosen substrate acts as both an active catalyst precursor and a conductive carrier. Here, a bifunctional catalyst, porous NiS/Ni9S8/NF-2 nanorods, was synthesized by low-temperature vulcanization after an oxalic acid etching process. To reach a current density of 10 mA cm−2, NiS/Ni9S8/NF-2 requires only a tiny overpotential of 115 mV for the HER and 176 mV for the OER, and demonstrates sustained activity for 100 hours with almost any degradation. The substrate self-derived NiS/Ni9S8/NF-2 catalyst for overall water splitting requires only a small voltage of 1.52 V to deliver 10 mA cm−2 with excellent stability. Experimental results show that the heterostructured electrocatalysts impart good catalytic properties of NiS/Ni9S8/NF-2 by modulating the electronic structure and promoting the reconstruction process from sulfides to hydroxides. This work demonstrates the success of the substrate self-derivation strategy to achieve high catalytic activity and provide a new autogenous growth technique for electrode fabrication. [ABSTRACT FROM AUTHOR]

Exploiting high-efficiency and durable electrocatalysts toward the methanol oxidation reaction (MOR) is crucial for the advancement of direct methanol fuel cells (DMFCs). Herein, we demonstrate the loading of platinum–palladium bimetallic nanoparticles (Pt–Pd NPs) onto poly(3,4-ethylenedioxythiophene) (PEDOT)-embellished titanium carbide (Ti3C2Tx) nanosheets as the electrocatalyst (Ti3C2Tx/PEDOT/Pt–Pd) via a facile and rapid chemical reduction-assisted one-pot hydrothermal process. The structural and morphological analyses of Ti3C2Tx/PEDOT/Pt–Pd indicate that the three-dimensional (3D) hybrid structure formed between PEDOT and Ti3C2Tx provides a sizable active surface and more active sites, which enhances the homogeneous dispersion of the Pt–Pd NPs and facilitates mass transfer. The Schottky junctions formed between PEDOT and Pt–Pd NPs contribute to charge transfer. The electronic effects and synergistic interactions between the support and catalyst favor the electrocatalytic activity of the catalyst. The electrochemical test results reveal that the Ti3C2Tx/PEDOT/Pt–Pd catalyst has prominent electrocatalytic capability for the MOR. Compared with Ti3C2Tx/Pt–Pd and commercial Pt/C catalysts, the Ti3C2Tx/PEDOT/Pt–Pd catalyst has a larger electrochemical activity surface area (ECSA = 122 m2 g−1) and higher mass activity (MA = 1445.4 mA mg−1), as well as better CO tolerance and more reliable long-term durability (a peak current density retention of 71% after 5200 s). [ABSTRACT FROM AUTHOR]

The electrocatalytic hydrogen evolution reaction (HER) is an ideal method for hydrogen production. Transition metal complex electrocatalysts exhibit poor HER activity due to excessive or weak adsorption of H during the electrochemical reduction of water to molecular hydrogen in acidic environments. Developing specific functional complex materials as desired catalysts is challenging. Here, an electrochemical surface restructuring strategy of polyoxometalate (POM)-modified Ag materials toward the HER with a dramatically decreased overpotential under acidic aqueous conditions is established. We prepared two POM [SiW12O40]4− (SiW12)/[P2W18O62]6− (P2W18)-based Ag-2,2′-biimidazole (H2biim) inorganic–organic hybrid compounds (1 and 2) via the hydrothermal method and these two compounds undergo an electrochemical restructuring process in 0.5 M H2SO4 during the HER, in which Ag nanoparticles are in situ formed with the basic structures of SiW12 and P2W18 being maintained. The activated catalysts (1-AC-RDE and 2-AC-RDE) exhibit good electrocatalytic activity for the HER with good long-term stability, and the required overpotentials at a current density of 10 mA cm−2 are 112 mV (1-AC-RDE) and 91 mV (2-AC-RDE) with Tafel slopes of 77 mV dec−1 and 65 mV dec−1, respectively. The excellent electron–proton storage and transferability of SiW12 and P2W18 may provide a solution for the insufficient capture of H by Ag, leading to an effective self-optimizing behavior and superior acidic HER activity. [ABSTRACT FROM AUTHOR]

A series of organometallic Re(I)(L)(CO)3Br complexes with 4′-substituted terpyridine ligands (L) has been synthesised as electrocatalysts for CO2 reduction. The complexes' spectroscopic characterisation and computationally optimised geometry demonstrate a facial geometry around Re(I) with three cis COs and the terpyridine ligand coordinating in a bidentate mode. The effect of substitution on the 4′-position of terpyridine (Re1–5) on CO2 electroreduction was investigated and compared with a known Lehn-type catalyst, Re(I)(bpy)(CO)3Br (Re7). All complexes catalyse CO evolution in homogeneous organic media at moderate overpotentials (0.75–0.95 V) with faradaic yields of 62–98%. The electrochemical catalytic activity was further evaluated in the presence of three Brønsted acids to demonstrate the influence of the pKa of the proton sources. The TDDFT and ultrafast transient absorption spectroscopy (TAS) studies showed combined charge transfer bands of ILCT and MLCT. Amongst the series, the Re-complex containing a ferrocenyl-substituted terpyridine ligand (Re5) shows an additional intra-ligand charge transfer band and was probed using UV-Vis spectroelectrochemistry. [ABSTRACT FROM AUTHOR]

Designing highly-efficient, cost-effective, and stable electrocatalysts for water splitting is essential to producing green hydrogen. In this work, a nanoflower quaternary heterostructured Ni(NO3)2(OH)4/Ni(OH)2/Ni3S2/NiFe-LDH electrocatalyst is successfully synthesized by two-step hydrothermal reactions. The sulfur in the electrocatalyst induces higher valence state metal atoms as active sites to accelerate the formation of O2. As expected, benefiting from the unique structural features and solid electronic interactions, Ni(NO3)2(OH)4/Ni(OH)2/Ni3S2/NiFe-LDH exhibits remarkable oxygen evolution reaction performance with a low overpotential of 223 mV at a current density of 100 mA cm−2, a slight Tafel slope of 65.4 mV dec−1, and outstanding stability in alkaline media. Attractively, using Ni(NO3)2(OH)4/Ni(OH)2/Ni3S2/NiFe-LDH as both a cathode and an anode, the alkaline electrolyzer delivers a current density of 10 mA cm−2 only at a cell voltage of 1.67 V, accompanied by superior durability. This work provides a facile method for the rational design of high-performance quaternary electrocatalysts. [ABSTRACT FROM AUTHOR]

Transition-metal sulfides (TMSs) have indeed drawn dramatic interest as a potential species of electrocatalysts by virtue of their unique structural features. However, their poor stability and inherent activity have impeded their use in electrocatalytic water splitting. Here, we provide a rational design of a hierarchical nanostructured electrocatalyst containing CeOx-decorated NiCo-layered double hydroxide (LDH) coupled with Ni3S2 protrusions formed on a Ni foam (NF). Specifically, the as-prepared electrocatalyst, denoted as Ni2Co1 LDH-CeOx/Ni3S2@NF, presents only 250 and 300 mV overpotential at ±100 mA cm−2, respectively, along with the Tafel slope values of 92 and 52 mV dec−1, as well remarkable long-term life for water splitting in an alkaline electrolyte. Based on systematic experiments and theoretical analysis, the superior electrocatalytic property in terms of Ni2Co1 LDH-CeOx/Ni3S2@NF can be imputed to the following reasons: the porous framework of Ni3S2@NF provides a largely surface area and high conductivity; the NiCo LDH nanosheets provide enriched active sites and favorable adsorption ability; the oxygen-vacancy-rich CeOx optimizes the electronic configuration. Overall, these factors work synergistically to expedite the catalytic kinetics of splitting water. Our work concentrates on a rational interface to devise efficient, multifunctional, and serviceable electrocatalysts for future applications. [ABSTRACT FROM AUTHOR]

It is imperative to develop bifunctional electrocatalysts with good activity and stability for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this paper, a hierarchical NiCo2O4/Ni3S2 hybrid is synthesized by direct growth on nickel foam (NF) using co-precipitation and sulfuration as a general two-step method. When the NiCo2O4/Ni3S2/NF material is used as an electrode, it displays high activity and perfect stability for OER. A low overpotential of only 360 mV is obtained at 40 mA cm−2, comparable to the benchmark of IrO2 electrodes (330 mV overpotential at 40 mA cm−2), benefiting from the particular hybrid structure of NiCo2O4/Ni3S2/NF with large surface area and fast electron transfer. In addition, the NiCo2O4/Ni3S2/NF sample also reveals a superior elevated HER activity compared to NiCo2O4/NF and NF catalysts individually, for which a low overpotential of only 143 mV is obtained at 10 mA cm−2. Beyond that, NiCo2O4/Ni3S2/NF is also used as a bifunctional water splitting catalyst, for which a very low cell voltage of 1.58 V is acquired at 10 mA cm−2 in 1.0 M KOH. The results reveal that oxide/sulfide-based materials can be used as a perfect electrode candidate and afford the advantage of the synergy strategy, which opens a new route toward desired water splitting electrochemical devices of high activity and environmentally friendly electrode materials. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is a promising energy conversion system, which has been studied a lot in recent years. However, owing to the high overpotential and sluggish kinetics of the OER, an efficient electrocatalyst is necessary to lower the overpotential and accelerate the reaction. In this paper, we report a cobalt phosphide (CoP)/carbon dots (CDs) composite as an electrocatalyst for the OER for the first time. A facile two-step method was used to synthesize the CoP/CDs composite and the concentration of CDs in the composite was further regulated. The experimental results show that when the amount of CDs in the composite is 6 mg (28.79 wt%C), the obtained CoP/CDs composite exhibits optimal electrocatalytic activity (with an overpotential of 400 mV in 1 M KOH at a current density of 10 mA cm−2) and high stability towards the OER. The good electrocatalytic activity of the composite is attributed to the small size of CoP and CDs and rapid electron transfer of CDs. [ABSTRACT FROM AUTHOR]

It is very important to design bi-functional materials for sustainable energy storage and conversion. NiO electrodes are promising candidates for supercapacitors and electrocatalysts, but the poor cycling stability limits their practical applications. To solve this issue, we prepared core–shell structured NiO@CoSe2 samples by a multi-step hydrothermal protocol. They exhibit a specific capacitance of 1130 C g−1 at a current density of 1 A g−1. An asymmetric device was assembled using the obtained product as the cathode. It delivers an energy density of 103.8 W h kg−1 at 2700 W kg−1. As an electrocatalyst for hydrogen evolution reactions, the NiO@CoSe2 sample presents an overpotential of 82.8 mV@10 mA cm−2 and a Tafel slope of 72.14 mV dec−1, respectively. [ABSTRACT FROM AUTHOR]

Recent years have seen an increasing interest in molecular electrocatalysts for the hydrogen evolution reaction (HER). Efficient hydrogen evolution would play an important role in a sustainable fuel economy, and molecular systems could serve as highly specific and tunable alternatives to traditional noble metal surface catalysts. However, molecular catalysts are currently mostly used in homogeneous setups, where quantitative evaluation of catalytic activity is non-standardized and cumbersome, in particular for multistep, multielectron processes. The molecular design community would therefore be well served by a straightforward model for prediction and comparison of the efficiency of molecular catalysts. Recent developments in this area include attempts at applying the Sabatier principle and the volcano plot concept – popular tools for comparing metal surface catalysts – to molecular catalysis. In this work, we evaluate the predictive power of these tools in the context of experimental operating conditions, by applying them to a series of tetraphenylporphyrins employed as molecular electrocatalysts of the HER. We show that the binding energy of H and the redox chemistry of the porphyrins depend solely on the electron withdrawing ability of the central metal ion, and that the thermodynamics of the catalytic cycle follow a simple linear free energy relation. We also find that the catalytic efficiency of the porphyrins is almost exclusively determined by reaction kinetics and therefore cannot be explained by thermodynamics alone. We conclude that the Sabatier principle, linear free energy relations and molecular volcano plots are insufficient tools for predicting and comparing activity of molecular catalysts, and that experimentally useful information of catalytic performance can still only be obtained through detailed knowledge of the catalytic pathway for each individual system. [ABSTRACT FROM AUTHOR]

Design and exploration of highly efficient oxygen evolution reaction (OER) electrocatalysts is an urgent task to realize the future ideals of the hydrogen economy. Non-precious metal-based nanomaterials have been widely developed as electrocatalysts to expedite reaction rate and solve the low efficiency problem of the OER. A novel nanocatalyst, NiSe-CoFe LDH, in which lamellar CoFe LDH covered the surface of NiSe, was fabricated through a simple chemical vapor deposition and hydrothermal method. The specific heterogeneous three-dimensional structure of NiSe-CoFe LDH showed impressive electrochemical performance towards the OER. When used as an OER electrocatalyst, the NiSe-CoFe LDH nanomaterial afforded an overpotential of 228 mV to attain 10 mA cm−2. Furthermore, NiSe-CoFe LDH also maintained excellent stability with negligible activity after chronopotentiometry measurement for 60 hours. [ABSTRACT FROM AUTHOR]

Hydrogen obtained through the electrolysis of water is a potential solution to the growing demand of human society for energy. In addition, water electrolysis generates less environmental pollution than fossil energy sources. However, the preparation of highly active and low-cost electrocatalysts remains a key challenge. Here, we report a facile and inexpensive method to prepare palladium nanoparticles (Pd NPs) supported on aminated (–NH2) metal–organic frameworks (MOF). The obtained electrocatalyst (Pd@Uio-66-NH2) exhibits excellent electrocatalytic performance for the hydrogen evolution reaction (HER), featuring an ultralow overpotential (34 mV at 10 mA cm−2), small Tafel slope (41 mV dec−1), and superior stability in acid electrolyte. Systematic characterization demonstrated that –NH2 can effectively stabilize palladium acetate as the Lewis base. Meanwhile, the strong interaction between the lone pair electrons and the d-orbital ensures that the Pd atoms are uniformly distributed in the MOF material, inhibiting the agglomeration of metal NPs in the reaction. This strategy provides an avenue to prepare inexpensive and highly active catalysts for HER in acidic media. [ABSTRACT FROM AUTHOR]

Rational construction of low-cost and high-performance electrocatalysts for water splitting is crucial for the advancement of renewable hydrogen fuel. Hybridizing heterojunctions or noble metals is one typical strategy used to boost the electrocatalytic performance for either the oxygen evolution reaction (OER) or hydrogen evolution reaction (HER). Here, low-content CeOx (3.74 wt%) is introduced into Ni3Fe nanoparticle-encapsulated carbon nanotubes (Ni3Fe@CNTs/CeOx), with both the OER and HER activities boosted, as a bifunctional electrocatalyst for overall water splitting. The composite is derived by pyrolyzing a mixture of melamine/ternary NiFeCe-layered double hydroxide. The composite electrocatalyst requires low overpotentials of 195 and 125 mV at 10 mA cm−2 in 1.0 M KOH, respectively, which are superior to those of Ni3Fe@CNTs/NF (313 and 139 mV) and CeOx/NF (345 and 129 mV), and in particular, OER overpotentials of 320 and 370 mV at 50 and 100 mA cm−2, respectively. Moreover, the composite-assembled electrolyzer for overall water splitting requires a current density of 10 mA cm−2 at a decent cell voltage of 1.641 V. Furthermore, the enhancement is elucidated by the synergistic effect: the dual role of CeOx in boosting the OER and HER, the highly conductive carbonaceous CNTs, large electrochemically active surface area and low charge-transfer resistance. The results can offer an effective route for designing and preparing low-cost and high-efficiency electrocatalysts for electrocatalytic water splitting. [ABSTRACT FROM AUTHOR]

The electrochemical decomposition of water plays a critical role in green and sustainable energy. However, the development of efficient and low-cost non-noble metal catalysts to overcome the high potential of the anodic oxygen evolution reaction (OER) is still challenging. In this work, electrocatalysts with high OER activity were obtained by doping Co/Fe bimetals into Ni3S2 (CF-NS) via a simple single-step hydrothermal method by adjusting the doping ratio of bimetals. A series of characterization studies revealed that the introduction of a Co/Fe co-dopant increased the number of active sites and improved the electroconductibility, while optimizing the electronic structure of Ni3S2. Meanwhile, Fe-induced high valence Ni contributed to the production of an OER active phase NiOOH. The unique dendritic crystal morphology facilitated the disclosure of the active sites and the expansion of mass transfer channels. The optimized sample required a low overpotential of 146 mV to obtain a current density of 10 mA cm−2 in 1.0 M KOH solution. The optimized sample also operated stably for at least 86 h. In sum, the proposed method looks very promising for designing efficient, stable, and low-cost non-precious metal catalysts with high conductivity and multiple active sites, useful for future synthesis of transition metal sulfide catalysts. [ABSTRACT FROM AUTHOR]

Stable and efficient bifunctional electrocatalysts are of great significance for sustainable energy conversion and human society sustainability. However, conventional electrocatalytic materials tend to exhibit high overpotentials and unsatisfactory chemical activities. Herein, we construct novel CoNi2S4/C3N4 nanowires on a nickel foam (NF) electrode as a bifunctional electrocatalyst for alkaline water splitting by a two-step hydrothermal and thermal annealing process. The prepared CoNi2S4/C3N4 electrocatalyst exhibits superior HER (e.g. 40 mV (ηH210)) and OER (e.g. 110 mV (ηO210)) activities in a 1 M KOH electrolyte, which are much smaller than those of bare NF, Co@NF, NiCoO@NF and most reported materials. Furthermore, the stability test at 10 mA cm−2 for 20 h for the CoNi2S4/C3N4 electrocatalyst shows no obvious decay and proves the excellent stability of CoNi2S4/C3N4. In this work, the unique tentacle-like CoNi2S4/C3N4 nanowire nanostructure leads to minimized interfacial resistance and abundant channels during electrocatalysis. Moreover, comprehensive analysis results show that Ni(Co)OOH active sites, which are beneficial for excellent OER activity, partially form on the surface of CoNi2S4/C3N4 during electrocatalysis. Finally, the CoNi2S4/C3N4∥CoNi2S4/C3N4 two-electrode system is constructed and it exhibits a low-voltage water splitting capability of 1.40 V. [ABSTRACT FROM AUTHOR]

The key step for hydrogen production through water electrolysis is the development of highly efficient and inexpensive oxygen evolution reaction (OER) catalysts. In this work, we report the successful synthesis of a nanostructured Fe-doped cobalt-based telluride (Fe-doped CoTe2) catalyst on Co foam by a simple one-step hydrothermal synthesis method, which shows excellent OER performance. The influences of Fe doping amounts and reaction temperatures on the morphology, structure, composition, and the OER performance of cobalt-based tellurides have been systematically studied. The optimal sample Co@0.3 g FeCoTe2-200 exhibits a low overpotential of 300 mV at a current density of 10 mA cm−2, and a small Tafel slope of 36.99 mV dec−1, outperforming the undoped cobalt telluride catalysts (Co@CoTe2-200). The Co@0.3 g FeCoTe2-200 electrode also reveals a small overpotential degradation of around 26 mV after an 18-hour continuous OER process. These results unambiguously confirm that Fe doping helps improve the OER activity and long-term catalytic stability. The superior performance of nanostructured Fe-doped CoTe2 can be attributed to the porous structure and the synergistic effect of Co and Fe elements. This study provides a new approach for the preparation of bimetallic telluride catalysts with enhanced OER performance, and Fe-doped CoTe2 holds substantial promise for use as a high-efficiency, cost-effective catalyst for alkaline water electrolysis. [ABSTRACT FROM AUTHOR]

Designing efficient non-precious electrocatalysts to boost water splitting for green energy is a worthy and crucial objective, while it is still an enormous challenge. Herein, single-phase Ni5P4 ultrathin porous nanosheets grown on Ni foam constructed using the three-dimensional single-phase hierarchical nanoflower Ni5P4 (defined as 3D SHF-Ni5P4) were assembled via a simple hydrothermal and phosphating process in an enclosed space. Benefitting from the special structure and morphology of 3D hierarchical porous ultrathin nanosheets, as well as their increasing number of active sites, the 3D SHF-Ni5P4 exhibited outstanding performance with low overpotentials of 180 mV and 106 mV for achieving a current density of 10 mA cm−2 in 1 M KOH toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), and the Tafel slopes were 54 mV dec−1 and 79 mV dec−1, respectively. The overall water separation setup, using 3D SHF-Ni5P4 as both the cathode and anode in 1.0 M KOH, achieved a current density of 10 mA cm−2 at a low voltage of 1.47 V, which surpasses that of the commercial Pt C/NF‖‖RuO2/NF (1.52 V). This work highlights an achievable strategy for the controllable fabrication of a 3D single-phase hierarchical nanoflower Ni5P4 electrocatalyst, constructed with ultrathin porous nanosheets containing plenty of active sites. It provided new insights into developing cost-effective single-phase electrocatalysts towards green energy by water splitting. [ABSTRACT FROM AUTHOR]

BiVO4 possesses a suitable band gap for photoelectrochemical (PEC) water splitting to produce hydrogen; however, the performance of BiVO4 is limited by several adverse factors. The bulk charge recombination and the slow surface water oxidation reaction of BiVO4 are main unfavorable factors. In view of these disadvantages, an Fe–Bi electrocatalyst is loaded on BiVO4 to improve the PEC performance of BiVO4. After modification, the onset potential of BiVO4 shifts negatively by 60 mV, and the saturated photocurrent is greatly increased. Systematic studies demonstrate that the Fe–Bi electrocatalyst not only enhances the bulk charge separation, but also accelerates the surface water oxidation rate of BiVO4 and greatly reduces the resistance of the reaction interface. [ABSTRACT FROM AUTHOR]

Progress in the development of efficient electrocatalysts for oxygen reduction reactions is imperative for various energy systems such as metal–air batteries and fuel cells. In this paper, an innovative porous two-dimensional (2D) poly-iron–phthalocyanine (PFe–Pc) based oxygen reduction electrocatalyst created with a simple solid-state chemical reaction without pyrolysis is reported. In this strategy, silicon dioxide nanoparticles play a pivotal role in preserving the Fe–N4 structure during the polymerization process and thereby assist in the development of a porous structure. The new polymerized phthalocyanine electrocatalyst with tuned porous structure, improved specific surface area and more exposed catalytic active sites via the 2D structure shows an excellent performance towards an oxygen reduction reaction in alkaline media. The onset potential (E = 1.033 V) and limiting current density (I = 5.58 mA cm−2) are much better than those obtained with the commercial 20% platinum/carbon electrocatalyst (1.046 V and 4.89 mA cm−2) and also show better stability and tolerance to methanol crossover. For practical applications, a zinc–air (Zn–air) battery and methanol fuel cell equipped with the PFe–Pc electrocatalyst as an air cathode reveal a high open circuit voltage and maximum power output (1.0 V and 23.6 mW cm−2 for a methanol fuel cell, and 1.6 V and 192 mW cm−2 for the liquid Zn–air battery). In addition, using the PFe–Pc electrocatalyst as an air cathode in a flexible cable-type Zn–air battery exhibits excellent performance with an open-circuit voltage of 1.409 V. This novel porous 2D PFe–Pc has been designed logically using a new, simple strategy with ultrahigh electrochemical performances in Zn–air batteries and methanol fuel cell applications. [ABSTRACT FROM AUTHOR]

Developing low-cost and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) has stimulated extensive interest. Molybdenum carbide materials have been proposed as promising alternatives to noble platinum-based catalysts due to their earth abundance and tunable physicochemical characteristics. Here, we report Mo2C@NC/Mo2C hollow microspheres composed of a β-Mo2C core and small β-Mo2C particles embedded within a nitrogen-doped carbon shell and prepared using guanosine and hexaammonium molybdate as precursors via a hydrothermal self-assembly process, which results in outstanding catalytic activity and fast kinetics in hydrogen evolution in both acidic and alkaline solutions. The significant activity improvement of Mo2C@NC/Mo2C can be attributed to the large ratio of exposed active sites and abundant interfacial structures. This work provides a new template-free strategy for the design of a highly active Mo2C@NC/Mo2C hollow microsphere HER catalyst. [ABSTRACT FROM AUTHOR]

OER (oxygen evolution reaction) is a critical reaction in several storage and conversion systems for renewable and clean electrochemical energies, including solar fuel devices, metal–air batteries, as well as regenerative fuel and water splitting cells. Regarding the shortcomings of OER, apart from the sluggish kinetics and high reaction overpotential, the reaction rate and overpotential are difficult to be optimized simultaneously. Herein, a novel hierarchical particle–sheet-structured Fe-doped NixP electrocatalyst is developed, which presents abundant interfaces between crystalline particle and amorphous sheet. The OER overpotential is reduced to 204 mV at 20 mA cm−2 current density, while it is reduced to 225 and 231 mV at 100 and 300 mA cm−2, respectively. The Fe-doped NixP electrocatalyst also shows fast reaction kinetics, whose Tafel slope is a remarkable 25 mV dec−1. For an electrolytic cell whose cathode and anode are Pt/C/NF and Fe–NixP/NF, respectively, a mere 1.446 V voltage is necessary to drive a 10 mA cm−2 current density for achieving overall water-splitting property. Notably, it also works stably at considerably high current densities of 500 and 1000 mA cm−2, representing high potential for commercial applications. [ABSTRACT FROM AUTHOR]

Electrochemically durable perovskite electrodes of nickel foam/TiO2/FA(Pb1−xGex)I3, passivated using various surfactants of tetra-n-alkyl ammonium halides (alkyl = ethyl, butyl, hexyl, or octyl; halide = I, I0.5Br0.5, Br, Br0.5Cl0.5, or Cl), were successfully applied as good electro-catalysts on the counter electrodes in dye-sensitized solar cells (DSSCs). The longer alkyl chain of a surfactant resulted in a higher water contact angle, but poorer film conductivity. Based on the optimal tetra-n-hexyl ammonium (THA) cation, shrinking the halide radius of THA from I to I0.5Br0.5 formed an appropriate amount of FAPbBr3 nano-crystals covering on the FA(Pb1−xGex)I3 grain surface. This phenomenon not only suppressed the perovskite decomposition under electrochemical measurements, but also created additional electro-catalytic active sites for triggering the iodide/triiodide redox reaction. Further shrinking the halide radius of THA from I0.5Br0.5 to Cl resulted in a severe self-aggregation of THACl, leading to an insufficient passivation and thereby poor electrochemical performance. In an ambient environment with a relative humidity higher than 75%, the optimal perovskite electrode of nickel foam/TiO2/FA(Pb1−xGex)I3-THAI0.5Br0.5 maintained the good crystallinity of α-FAPbI3 at least for 6 months, without obvious decomposition. Compared to the DSSC couple with a common counter electrode of nickel foam/Pt (8.74%), a better cell performance of 8.87% was achieved using the counter electrode of nickel foam/TiO2/FA(Pb1−xGex)I3-THAI0.5Br0.5, which was attributed to its good intrinsic electro-catalytic activity, large surface area, multiple active sites, and decent thermodynamic stability. Under room light illumination, higher cell efficiencies were obtained at 1 klux (21.5% for an office), 3 klux (22.9% for a shopping window), and 6 klux (22.3% for a lampshade). There is no doubt that air-stable perovskites have great potential in showing high performance for various electrochemical devices. [ABSTRACT FROM AUTHOR]

The development of electrode materials with abundant active surface sites is important for large-scale hydrogen production by water electrolysis. In this study, Fe/Ni NWs/NF catalysts were prepared by hydrothermal and electrochemical deposition of iron nanosheets on nickel chain nanowires, initially grown on nickel foam. The synthesized Fe/Ni NWs/NF electrode possessed a 3D layered heterostructure and crystalline−amorphous interfaces, containing amorphous Fe nanosheets, which demonstrated excellent activity in the oxygen evolution reaction (OER). The newly prepared electrode material has a large specific surface area, and its electrocatalytic performance is characterized by a small Tafel slope and an oxygen evolution overpotential of 303 mV at 50 mA cm−2. The electrode was highly stable in alkaline media with no degradation observed after 40 h of continuous OER operation at 50 mA cm−2. The study demonstrates the significant promise of the Fe/Ni NWs/NF electrode material for large-scale hydrogen production by water electrolysis and provides a facile and low-cost approach for the preparation of highly active OER electrocatalysts. [ABSTRACT FROM AUTHOR]

Developing high-performance and low-cost bifunctional oxygen electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is of great significance for accelerating the commercialization of rechargeable zinc–air batteries (RZABs). Herein, in situ grown Co3O4 nanoparticle-embedded N-doped hollow porous carbon nanospheres (Co3O4@N-HPCNs) are synthesized via template-assisted pyrolysis as efficient bifunctional ORR/OER electrocatalysts. The N-HPCNs efficiently seize and confine Co3O4 nanoparticles to enhance electronic conductivity and structural stability, while the hollow porous architecture offers adequate mass diffusion pathways to improve the accessibility of reactants and electrolytes on active sites. Therefore, the as-obtained Co3O4-10%@N-HPCNs display outstanding activity and stability for the ORR and the OER, even outperforming commercial Pt/C and Ru/C catalysts. Liquid RZABs assembled with Co3O4-10%@N-HPCN cathodes exhibit a large specific capacity of 768.3 mA h g−1Zn, a high peak power density of 145.6 mW cm−2 and a long-term cycling stability for over 1000 h, demonstrating much-enhanced battery performance in comparison with that of Pt/C + Ru/C based RZABs. Also, flexible quasi-solid-state RZABs assembled with Co3O4-10%@N-HPCN cathodes exhibit a considerable power density of 132.0 mW cm−2 and a stable charge–discharge voltage for a long period even upon bending. This work provides a new approach for the development of catalysts with high activity, long-term stability and low cost. [ABSTRACT FROM AUTHOR]

The widespread use of proton-exchange membrane water electrolysis is limited by the dynamically sluggish oxygen evolution reaction (OER), which is mediated by noble iridium-based materials as active and stable electrocatalysts. Significant efforts have been made to decrease the amount of iridium in OER catalysts without sacrificing their catalytic performances. In this frontier paper, we present the main common issues relevant to the iridium-catalyzed OER, including catalytically active species, catalytic mechanisms and activity-stability relation. We also take iridium-based perovskites as an example, and summarize the recent theoretical and experimental advances in available strategies that can lead to highly efficient, low-iridium oxygen evolution electrocatalysts under acidic conditions. Finally, we propose the remaining challenges and future directions for exploring acidic OER catalysts. [ABSTRACT FROM AUTHOR]

High activity bifunctional oxygen electrocatalysts are crucial for the development of high performing Zn–air batteries. Fe–N–C systems decorated with Fe/Fe3C nanoparticles have been identified as prospective candidates in which almost all the active sites need the presence of N. To anchor more N, an Fe2O3 microsphere template was covered by a thin layer of polymerized dopamine (PDA) before it was mixed with a high N-content source of g-C3N4. The PDA interlayer not only provides a part of C and N but also serves as a buffer agent to hinder fast reactions between Fe2O3 and g-C3N4 during pyrolysis to avoid the destruction of the microsphere template. The prepared Fe/Fe3C@FeNC catalyst showed superior electrochemical performance, achieving a high half-wave potential of 0.825 V for ORR and a low overpotential of 1.450 V at 10 mA cm−2 for OER. The rechargeable Zn–air battery assembled with the as-obtained Fe/Fe3C@FeNC catalyst as a cathode offered a high peak energy density of 134.6 mW cm−2, high specific capacity of 856.2 mA h gZn−1 and excellent stability over 180 h at 5 mA cm−2 (10 min per cycle) with a small charge/discharge voltage gap of ∼0.851 V. This work presents a practical strategy for constructing nitrogen-rich catalysts with stable 3D structures. [ABSTRACT FROM AUTHOR]

The rational design of a highly efficient oxygen evolution reaction (OER) is crucial for the practical applications of water electrolysis. Herein, a hybrid Co3O4@FeOOH/NF electrode was fabricated by loading FeOOH sheets on the surface of Co3O4 nanosheet arrays via a newly developed chemical deposition protocol. The decoration of FeOOH on Co3O4 nanosheet arrays not only endows a strong electronic interaction between the two components but also offers sufficient active sites for the OER process. Benefitting from these advantages, Co3O4@FeOOH/NF exhibited outstanding OER activity in terms of a low overpotential of 209 mV at 10 mA cm−2 and a low Tafel slope of 48.9 mV dec−1. Moreover, nearly steady state operation current and negligible change in the phase and morphology of the catalyst also indicate remarkable stability. This work may provide an important guide for the design of high-performance electrocatalysts for energy conversion applications. [ABSTRACT FROM AUTHOR]