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Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has received increasing attention as it is an eco-friendly strategy for synthesizing a key monomer for the production of bio-based plastics. Developing efficient, low-cost and stable electrocatalysts is crucial for this electrochemical reaction. In this work, we have reported a facile process for the synthesis of hybrid nanosheet-structured NiCo2O4 on carbon fiber paper (NiCo2O4-CFP) for the efficient electrochemical conversion of HMF into FDCA. As a non-noble binary metal-based catalyst, NiCo2O4-CFP featured a nanosheet network and 3D nanosheet flower-like microspheres, showing 94.3% selectivity and 89.6% faradaic efficiency (FE) for FDCA, which outperformed its single component metal oxides NiO-CFP and Co3O4-CFP. And it also exhibited relatively high stability by maintaining over 80% FE after four successive cycles. The proposed mechanism suggested that the synergistic effect of Ni and Co elements in NiCo2O4 could facilitate HMF oxidation. [ABSTRACT FROM AUTHOR]

Designing cost-effective, highly efficient and stable electrocatalysts for oxygen evolution reaction is of paramount importance. Although extensive studies have focused on the relatively cheaper 3d transition metal oxide catalysts, the effect of trimetallic composites on the catalytic ability still remains elusive. Herein, we selected FeCo catalyst as the platform and investigated the catalytic activity of trimetallic composites, which were synthesized by incorporating Mo, W or Ni into the FeCo catalyst. The experimental results evidenced that FeCoMo/CP exhibited high catalytic activity towards water oxidation in alkaline solution, which required an overpotential of only ∼270 mV. Such impressive catalytic performance of FeCoMo/CP can be attributed to the fact that the introduction of Mo appreciably modulated the electronic structure of the Fe and Co centers, leading to an enhancement in intrinsic active sites. Benefiting from the tight contact with the highly conductive carbon paper substrate, FeCoMo/CP showed excellent stability up to 120 h. These results indicate that the surface engineering of FeCo-based catalysts by incorporating non-noble metals is a rational strategy to promote the performance of electrocatalysts. [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]

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]

As a versatile and environmentally friendly chemical, hydrogen peroxide (H2O2) is in high demand. The current anthraquinone oxidation process suffers from high energy consumption in hydrogen production and the cumbersome alternating operations of hydrogenation and oxidation. The direct synthesis of H2O2 from H2 and O2 is constrained by the balance between safety and efficiency and heavy metal pollution from catalysts. Two-electron oxygen reduction reaction (2e− ORR) is an efficient, safe, and low-cost route for the production of H2O2. This 2e− ORR pathway has potential to become a supplement to the anthraquinone process because of fossil energy-free feature. The bottleneck of the industrialization of 2e− ORR is the lack of efficient catalysts. The 2e− ORR catalytic performance of noble metal electrode materials urgently needs to be significantly enhanced by smart design. However, the high price and limited reserves of these noble metal-based materials still severely limit their commercialization. Among many 2e− ORR catalysts, carbon-based catalysts have received much attention because of their low cost and diverse structures. This study reviews the research progress and the synthesis methods of carbon-based catalysts for 2e− ORR in recent years. First, this paper introduces the fundamental mechanism of H2O2 production by 2e− ORR through a combination of theory and experiment. Then, the synthesis methods and optimization strategies of various high-efficiency carbon-based catalysts are discussed. Finally, the various influencing factors (pH effect, pore structure, and carbon defects) and the practical applications for H2O2 production are analyzed. In addition, the future research direction is also proposed to promote the development of carbon-based catalysts for 2e− ORR toward industrialization. Although carbon-based catalysts display obvious advantages for electrocatalytic applications, there are still a few shortcomings that need to be overcome. The intrinsic activity and the long-term stability of carbon-based materials still require to be improved to a level that can be compared with those of noble metal-based catalysts. This review presents a comprehensive overview of the latest developments in the production of H2O2 by 2e− ORR on carbon-based catalysts, combining the most advanced theoretical and experimental literature available. The current state of the research on carbon-based catalysts in recent years indicates great promise for further advancement. [ABSTRACT FROM AUTHOR]

Nickel-based electrocatalysts for the oxygen evolution reaction (OER) show the disadvantages of low activity and poor stability. In this paper, an FeNi alloy is wrapped by an amino-modified MOF-5-derived N-doped carbon layer to address these problems. Additionally, the improvement resulting from Fe doping of NiOOH catalysts is theoretically supported. [ABSTRACT FROM AUTHOR]

Cu–Pd bimetallic catalysts were fabricated on carbon paper (CP) by the electrodeposition method via a dynamic hydrogen bubble template approach. At a potential of −1.2 V vs. RHE, the Faradaic efficiency (FE) of C2H4 could reach 45.2% with a current density of 17.4 mA cm−2 in an H-type electrolytic cell. Detailed studies suggest that the enhanced performance of Cu–Pd/CP was attributed mainly to the synergistic effect, low interfacial charge transfer resistance, and the 3D architecture of the catalysts. [ABSTRACT FROM AUTHOR]

The development of high-performance and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is critical to renewable energy conversion and storage technologies. Among of them, metal organic frameworks (MOFs) have been proved to be effective substitutes for precious metals. In this paper, a series of mixed NiCoFe-MOFs with low crystallinity were synthesized by a simple one-step solvothermal method, which can be used as a direct electrocatalyst for the OER. Notably, the flower-like nanocatalyst NiCoFe-MOF-2 exhibits a hierarchical pore network and a large specific surface area (149.6 m2 g−1), which results in an adjustable electronic structure, effective mass transfer, and abundant exposed active sites. In addition, due to the synergy between the three metals Fe, Co and Ni, NiCoFe-MOF-2 can exhibit excellent electrocatalytic OER performance, with a low overpotential of 321 mV at 10 mA cm−2, superior to commercial RuO2 (379 mV), a Tafel slope of 48 mV dec−1 and long-term stability. The result may stimulate more designs of MOF-derived catalysts with multi-scale structures and multi-components designed for various electrochemical energy conversion devices. [ABSTRACT FROM AUTHOR]

The development of noble-metal-free electrocatalysts with high catalytic efficiency, low cost, and high durability in pH-universal media is encountering a bottleneck in practical applications. In this paper, Ni@MoN-700 coral hybrids were prepared using hydrogen evolution reaction (HER) catalysts, which were synthesized by a high-temperature reduction of NiMoO4 nanorods with urea. It was found that the annealing temperature seriously affects the surface morphology and chemical composition of the catalysts. Besides, structural reorganization occurred during the HER, which involved the joining of pyrrolic N, metal nitrogen, Mo3+, and Mo6+, governing the HER performance. Also, during the HER, Ni and Mo could synergistically improve the overall catalytic activity of the catalysts, via electronic interactions. These advantages endow Ni@MoN-700 with exceptional endurance and great HER activity, with a low overpotential of 30 mV and 76 mV at 10 mA cm−2 in alkaline and acidic media. These characteristics are similar to those of Pt under alkaline conditions. NiMoN catalysts show unusual activity and long-term stability, indicating a wide range of potential applications. [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]

The rational design of high-efficiency electrocatalysts for application in water oxidation in alkaline media remains a great challenge. In this paper, Ni3+-rich nanograss-like Mo-doped Ni3S2/NiS/VS arrays grown on nickel foam (denoted as Mo-NiVS@NF) have been successfully constructed through a hydro/solvothermal method. Interestingly, Mo-NiVS@NF exhibits superior catalytic OER performance, needing an overpotential of 217 mV to drive a current density of 10 mA cm−2, outperforming most previously reported NiS-based electrocatalysts. The result indicates that the Ni3+-rich active sites caused by the modulation of the electronic structure environment via the introduction of V and high-valency Mo play an important role in the high activity for the OER. Moreover, this catalyst shows high long-term electrochemical durability. [ABSTRACT FROM AUTHOR]

Exploring active catalyst components is very important to develop high-performance and highly stable ORR electrocatalysts to replace costly Pt-based catalysts, though it remains an ongoing challenge. In this paper, three ORR catalysts with different active components were obtained by calcination of different proportions of mixed precursors simply and delicately. Among them, precursor 1 (bimetallic polymer Fe/Zn-ZIFs@ZnCO3) played the role of a self-sacrificing template, while precursor 2 (an N, P-co-doped polymer) played the role of a volatile atmosphere. Precursor 2 also embedded N and P heteroatoms into the carbon framework during high-temperature volatilization, which resulted in subtle changes in the active catalyst components. Finally, a hybrid of metal Fe and α-Fe2O3 nanoparticles embedded in N, P-codoped carbon nanotubes with many separated gullies (named α-Fe2O3/Fe@NPC) exhibited excellent ORR catalytic activity in an alkaline solution as compared to commercial Pt/C. This work provides a new strategy for designing controllable active components using volatile precursors. [ABSTRACT FROM AUTHOR]

Water electrolysis is one of the most promising approaches for producing hydrogen. However, the OER, kinetics are sluggish and necessitate highly efficient electrocatalysts to speed up the reaction. In this work, we used NiCo glycerate solid nanospheres as a precursor to construct Fe–Ni–Co trimetallic oxide nanospheres utilizing a solvothermal-annealing and stirring technique. The oxygen evolution reaction (OER) activity of the Fe–Ni–Co spheres was greatly enhanced after Fe doping. Among these samples, the FeNiCo-15 hierarchical yolk–shell spheres needed overpotentials of only 204 and 178 mV for the OER and HER, respectively, to drive a current density of 10 mA cm−2, and showed good electrochemical stability. Further, it also presented superior electrocatalytic activity in terms of full water splitting, which was comparable to the integrated performance of the Pt‖IrO2 couple. A cell voltage of only 1.61 V was required to attain a current density of 10 mA cm−2. This paper provides a promising method for developing efficient bifunctional electrocatalysts driving redox electrocatalysis. [ABSTRACT FROM AUTHOR]

Hydrogen energy is a promising energy source that is environmentally friendly due to its long-term, large-capacity storage and low greenhouse gas emissions. However, the mass production of hydrogen is still technically difficult due to limitations in efficiency, stability, and cost, even though it can satisfy all of the current energy demands. Water splitting using an electrocatalyst is an efficient method for environmentally friendly hydrogen production, and various catalyst-related studies are being conducted for this purpose. For the last decade, transition metal-based compositions have been at the center of water splitting catalyst research. Despite numerous studies and developments, studies on transition metal-based catalysts so far still have various problems to be solved. Although excellent review papers on transition metal-based catalysts have been reported, the overall scope of transition metal-based catalysts has rarely been covered in the reports. In this review, we present the research about overall transition metal-based electrocatalysts for hydrogen production from four different categories, namely, alloys, transition-metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and single-atom catalysts (SACs). The fundamental roles of metal alloying and unique electrical properties of TMDs, LDHs, and SACs are mainly discussed. Furthermore, we present the recent advances in photovoltaic–electrochemical (PV–EC) systems for sustainable hydrogen production. Finally, perspectives on the issues to be addressed in the research on transition metal-based electrocatalysts are provided. [ABSTRACT FROM AUTHOR]

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are one type of promising energy device with the advantages of fast reaction kinetics (high energy efficiency), high tolerance to fuel/air impurities, simple plate design, and better heat and water management. They have been expected to be the next generation of PEMFCs specifically for application in hydrogen-fueled automobile vehicles and combined heat and power (CHP) systems. However, their high-cost and low durability interposed by the insufficient performance of key materials such as electrocatalysts and membranes at high temperature operation are still the challenges hindering the technology's practical applications. To develop high performance HT-PEMFCs, worldwide researchers have been focusing on exploring new materials and the related technologies by developing novel synthesis methods and innovative assembly techniques, understanding degradation mechanisms, and creating mitigation strategies with special emphasis on catalysts for oxygen reduction reaction, proton exchange membranes and bipolar plates. In this paper, the state-of-the-art development of HT-PEMFC key materials, components and device assembly along with degradation mechanisms, mitigation strategies, and HT-PEMFC based CHP systems is comprehensively reviewed. In order to facilitate further research and development of HT-PEMFCs toward practical applications, the existing challenges are also discussed and several future research directions are proposed in this paper. [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]

Efficient electrocatalysts are in great demand for renewable energy storage systems. Herein, we propose an ultrafast heating strategy to fabricate an efficient Ir/CP-UH catalyst for the oxygen evolution reaction (OER). Experimental results demonstrated that the ultrasmall Ir nanoparticles (≈1–3 nm) and clusters (<1 nm) were highly dispersed on the carbon paper support after a short thermal shock (∼5 s). The catalyst showed a low overpotential of 260 mV at 10 mA cm−2 and remarkable mass activity of about 13.8 times higher than that of the current state-of-the-art commercial Ir/C catalyst. This ultrafast heating strategy can also be applied to other catalyst systems for OER and other electrochemical reactions. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting, which is driven by renewable energy input to produce oxygen, has been widely regarded as a promising strategy in the future energy portfolio. The two-dimensional structure based on CoOOH nanosheets is easy to handle in the preparation process, low in cost, and has a small overpotential during water decomposition. Therefore, CoOOH two-dimensional materials have been widely used as electrocatalysts for the oxygen evolution reaction (OER). In this paper, we summarize the application of two-dimensional CoOOH nanosheets in the field of oxygen production from electrocatalytic water splitting. First, the different preparation methods of two-dimensional CoOOH nanosheets are briefly introduced. The structure–activity relationship of the two-dimensional CoOOH catalyst was analyzed from different viewpoints, such as doping, defects, etc. Finally, different catalytic mechanisms of CoOOH-based catalysts are discussed, and studies at the density functional theory (DFT) level are also provided to support the above mechanisms. To improve the readability of this review, a concise overview at the end of each section is given to illustrate some of the characteristics and trends of the studies in the corresponding part. The opportunities and challenges of two-dimensional CoOOH as an electrocatalyst in the future are summarized in the Conclusion section. This work will provide new insights and perspectives to the readers to understand the role of CoOOH nanosheets in the OER process. [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]

Interface engineering is the most direct and efficient way to enhance the oxygen evolution reaction (OER) activity of transition-metal sulfides (TMSs). However, present methods of engineering nano-interfaces remain to be improved. Here, we present a nitrate-pyrolysis method to create a sulfide–oxide interface on Cu2S for the first time. Specifically, a CoOx decorated Cu2S nanowire array on Cu foam (Cu2S–CoOx/CF) is prepared successfully, and the XPS result demonstrates the interfacial connection between Cu2S and CoOx. To afford a current density of 25 mA cm−2, Cu2S–CoOx/CF needs an overpotential of 255 mV, lower than that of Cu2S/CF (354 mV) and CoOx/CC (378 mV). These results indicate that the introduction of the sulfide–oxide interface is an efficient means to enhance the OER activity of Cu2S. And this paper should provide a novel route for more explorations in interface engineering for TMSs. [ABSTRACT FROM AUTHOR]

We report a novel and facile route to improve the catalytic performance of carbon paper-based electrocatalysts, which can be activated by in situ discharging with the assistance of a Li cell. Our results show that the OER potentials were successfully reduced to ∼3.5 V, much lower than the value of 4.5 V for graphite paper, which is the best result recorded amongst the reported carbon-based electrocatalysts. [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]

Electrocatalysis plays a central role in clean energy conversion, enabling a number of processes for future sustainable technologies. Atomic site electrocatalysts (ASCs), including single-atomic site catalysts (SASCs) and diatomic site catalysis (DASCs), are being pursued as economical alternatives to noble-metal-based catalysts for these reactions by virtue of their exceptionally high atom utilization efficiencies, well-defined active sites and high selectivities. In this review, we start from a systematic review on the fabrication routes of ASCs followed by an overview of some new and effective characterization methods to precisely probe the atomic structure. Then we give a comprehensive summary on the current advances in some typical clean energy reactions: water splitting, including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER); oxygen reduction reaction (ORR), including selective 4e− – ORR toward H2O/OH− and 2e− – ORR toward H2O2/HO2−; selective electrooxidation of formic acid, methanol and ethanol (FAOR, MOR and EOR). At the end of this paper, we present a brief conclusion, and discuss the challenges and opportunities on the further development of more selective, active, stable and less expensive ASCs. [ABSTRACT FROM AUTHOR]

The development of earth-abundant and high-efficiency electrocatalysts for overall water splitting is highly fascinating and still presents a challenge caused by the low activity for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at the same time. In this paper, active cobalt-doped pyrite nanospheres with a porous structure are fabricated for the first time as advanced catalysts for water splitting in an alkaline solution. With the incorporation of cobalt atoms, the electronic structure of pyrite is well-tuned, with high conductivity as well as more active sites being obtained, which finally results in a superior bifunctional water splitting performance. Only 1.60 V is required to reach the current density of 10 mA cm−2, which is smaller than that of other transition metal sulfides. [ABSTRACT FROM AUTHOR]

The fine design of three-dimensional (3D) nanocatalysts has attracted great research interest, particularly in fuel cells. In this paper, 3D porous PdSn alloy networks were successfully synthesized for the first time at 60 °C by a facile self-assembly method without using any surfactants. Through comprehensive physical characterization, the formation of a porous network structure with an average diameter of 7 nm was confirmed. The as-prepared PdSn alloy networks exhibited greatly enhanced catalytic performance towards formic acid oxidation (FAO) compared to Pd/C, which could be ascribed to their self-supported network nanostructure, the multifunctional effect between Pd and Sn and the particularly "clean" surface. Also, the widespread amorphous SnO2 greatly enhanced the stability of the network catalysts. Among the three different atomic ratios of PdSn networks, the Pd2Sn1 sample exhibited the highest peak current density (1.35 A mgpd−1), which was 2.3-fold higher than that of Pd/C. After chronoamperometric testing for 3600 s, the Pd2Sn1 networks still showed the highest mass activity (0.16 A mgpd−1), which was 16-fold higher than that of Pd/C. Furthermore, the Pd2Sn1 catalyst displayed the best performance for FAO among all reported PdSn network catalysts. Therefore, after surface electron and geometry modification, the as-obtained PdSn alloy networks can be applied as state-of-the-art electrocatalysts for direct formic acid fuel cells. [ABSTRACT FROM AUTHOR]

It is significant to develop economically cheaper, more environmentally friendly bifunctional electrocatalysts for both water reduction reaction (WRR) and water oxidation reaction (WOR). In this paper, a NiO/Ni3S2 core–shell hybrid directly grown on nickel foam is constructed using a simple two-step hydrothermal and sulfuration method. When the NiO/Ni3S2/NF electrode is first tested as a catalyst, it reveals a high catalytic activity and durability for WOR. The smaller overpotential of only 270 mV obtained at 30 mA cm−2 is better than the benchmark of precious metal RuO2 materials (410 mV @ 30 mA cm−2), benefiting from the unique hierarchical structure of NiO/Ni3S2/NF with more active sites and fast electron transfer. Moreover, the NiO/Ni3S2/NF electrode also exhibits a fairly good WRR performance compared with the individual NiO/NF and NF electrodes, showing a smaller overpotential of only 130 mV at 10 mA cm−2. In addition to this, a very low cell voltage of 1.59 V is obtained at 10 mA cm−2 in 1.0 M KOH, when NiO/Ni3S2/NF is also tested as a bifunctional water splitting electrode. The experimental results indicate that the oxide/sulfide-based catalysts could serve as an ideal electrode candidate and bring the superiority of a synergistic strategy into full play, which offers a new idea toward the development of efficient and environmentally friendly water splitting electrochemical electrode materials. [ABSTRACT FROM AUTHOR]

Combining photochemical and electrochemical energy conversion into a single catalytic system is an efficient method for energy generation. In this paper, to increase the electrocatalytic activity of 2H-WS2 nanosheets, CdSe quantum dots (QDs) are introduced as sensitizers to design a novel photo-responsive electrode. The electrocatalytic HER activity of the nanocomposites is observably enhanced under 300 W Xe lamp irradiation (λ≥ 420 nm, the overpotential decreases from −1030 mV vs. RHE to −400 mV vs. RHE at a cathodic current density of 10 mA cm−2 in neutral electrolyte without adding any sacrificial agent, and the Tafel slope decreases from 132 mV dec−1 to 56 mV dec−1). Moreover, the photo-enhanced electrocatalyst demonstrates high stability, which is reflected by a steady-state performance for more than 24 h. This strategy may have potential use in designing and fabricating novel photo-assisted electrocatalysts. [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]

Chemical and electrochemical corrosion of a support limits the corresponding catalyst's performance and lifetime. In this paper, uniform TiN nanotubes are synthesized via coaxial-electrospinning, thermal oxidation and nitridation. The average diameter of nanotubes can be facilely controlled by tuning the parameters of coaxial electrospinning. The TiN nanotubes are modified further with Pt nanoparticles as Pt/TiN NT electrocatalysts. After accelerated durability tests, the electrochemical surface area (ECSA) and mass activity of the Pt/TiN decrease by only 6% and 14% respectively, while those of the Pt/C decrease by 44% and 46.2% respectively. The enhanced activity is attributed to the strong interaction between the Pt nanoparticles and the TiN support, which is confirmed by the X-ray dispersive spectra of Pt 4f. [ABSTRACT FROM AUTHOR]

It is regarded that transition metal complexes can catalyze hydrogen production via an unstable metal-hydride species, and the reduction reaction occurs at the metal center. In this paper, we present a new catalytic mechanism via ligand-centered proton-transfer for hydrogen generation catalyzed by a coordinatively saturated nickel complex, [NiII(L)2] 1, which is obtained by the reaction of the triazenido ligand, 1,3-bis[2-aminobenzothiazole]triazene (HL), with Ni(CH3CO2)2. Electrochemical investigations show that the electrocatalytic system based on [NiII(L)2] can afford 76.31 and 685.76 moles of hydrogen per mole of catalyst per hour (mol H2/mol catalyst/h) from acetic acid at an overpotential (OP) of 991.6 mV and from a neutral aqueous buffer (pH 7.0) at an OP of 837.6 mV, respectively. [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]

Electrocatalysts for H2 production are envisioned to play an important role in renewable energy utilization systems. Nickel-based catalysts featuring pendant amines functioning as proton relays in the second coordination sphere of the metal center have led to catalysts achieving turnover frequencies as high as 107 s−1 for H2 production. The fastest rates are observed when water is present in solution, with rates up to 103 times faster than those found in dry solvent. The focus of this paper is to provide mechanistic insight into the unexpected enhancement due to water. Addition of H2 to [Ni(PCy2NR′2)2]2+ was previously shown to give three isomers of a Ni(0) product with two protonated amines, where the N–H can be endo or exo to the Ni. By investigating the deprotonation of these two N-protonated Ni(0) intermediates resulting from the addition of H2 to [Ni(PCy2NR′2)2]2+, we observe by NMR spectroscopy studies an enhancement in the rate of deprotonation for protons positioned on the pendant amine next to the metal (endo) vs. protons that are positioned away from the metal (exo). Computational studies suggest that for smaller bases, the desolvation energy of the exogenous base is the primary contribution limiting the rate of endo deprotonation, while steric accessibility and facile proton movement also contribute. For more bulky bases, steric accessibility can play the dominant role. The significant reduction in these barriers observed in the presence of water has important implications for disfavoring less productive catalytic pathways and increasing catalytic rates. [ABSTRACT FROM AUTHOR]

This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO2) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO-, CH2O, CH4, H2C2O4//HC2O4-, C2H4, CH3OH, CH3CH2OH and others. The electrocatalysts are classified into several categories, including metals, metal alloys, metal oxides, metal complexes, polymers/clusters, enzymes and organic molecules. The catalyts' activity, product selectivity, Faradaic efficiency, catalytic stability and reduction mechanisms during CO2 electroreduction have received detailed treatment. In particular, we review the effects of electrode potential, solution-electrolyte type and composition, temperature, pressure, and other conditions on these catalyst properties. The challenges in achieving highly active and stable CO2 reduction electrocatalysts are analyzed, and several research directions for practical applications are proposed, with the aim of mitigating performance degradation, overcoming additional challenges, and facilitating research and development in this area. [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]

We demonstrate a lamellar NiMoCo@CuS catalyst, showing not only an excellent catalyst performance (η100@72 mV and a Tafel slope of 47 mV dec−1), but also a good stability (20 mA cm−2@30 hours), outperforming the NiMo system and noble Pt. [ABSTRACT FROM AUTHOR]