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High-entropy compounds have been emerging as promising candidates for electrolysis, yet their controllable electrosynthesis strategy remains a formidable challenge because of the ambiguous ionic interaction and codeposition mechanism. Herein, we report a oxygenates directionally induced electrodeposition strategy to construct high-entropy materials with amorphous features, on which the structural evolution from high-entropy phosphide to oxide is confirmed by introducing vanadate, thus realizing the simultaneous optimization of composition and structure. The representative P-CoNiMnWVOx shows excellent bifunctional catalytic performance toward alkaline hydrogen evolution reaction and ethanol oxidation reaction (EOR), with small potentials of -168 mV and 1.38 V at 100 mA cm-2, respectively. In situ spectroscopy illustrates that the electrochemical reconstruction of P-CoNiMnWVOx induces abundant Co-O species as the main catalytic active species for EOR and follows the conversion pathway of the C2 product. Theoretical calculations reveal the optimized electronic structure and adsorption free energy of reaction intermediates on P-CoNiMnWVOx, thereby resulting in a facilitated kinetic process. A membrane-free electrolyzer delivers both high Faradaic efficiencies of acetate and H2 over 95% and superior stability at100 mA cm-2 during 120 h electrolysis. In addition, the unique composition and structural advantages endow P-CoNiMnWVOx with multifunctional catalytic activity and realize multipathway electrosynthesis of formate-coupled hydrogen production.
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Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.
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Exploiting highly active and bifunctional catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) is a prerequisite for the hydrogen acquisition. High-entropy materials have received widespread attention in catalysis, but the high-performance bifunctional electrodes are still lacking. Herein, a novel P-modified amorphous high-entropy CoFeNiCrMn compound is developed on nickel foam (NF) by one-step electrodeposition strategy. The achieved CoFeNiCrMnP/NF delivers remarkable HER and HzOR performance, where the overpotentials as low as 51 and 268 mV are realized at 100 mA cm-2 . The improved cell voltage of 91 mV is further demonstrated at 100 mA cm-2 by assessing CoFeNiCrMnP/NF in the constructed hydrazine-assisted water electrolyser, which is almost 1.54 V lower than the HER||OER system. Experimental results confirm the important role of each element in regulating the bifuncational performance of high-entropy catalysts. The main influencing elements seem to be Fe and Ni for HER, while the P-modification and Cr metal may contribute a lot for HzOR. These synergistic advantages help to lower the energy barriers and improve the reaction kinetics, resulting in the excellent bifunctional activity of the CoFeNiCrMnP/NF. The work offers a feasible strategy to develop self-supporting electrode with high-entropy materials for overall water splitting.
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Electrocatalytic N2 reduction reaction (NRR) into ammonia (NH3), especially if driven by renewable energy, represents a potentially clean and sustainable strategy for replacing traditional Haber-Bosch process and dealing with climate change effect. However, electrocatalytic NRR process under ambient conditions often suffers from low Faradaic efficiency and high overpotential. Developing newly regulative methods for highly efficient NRR electrocatalysts is of great significance for NH3 synthesis. Here, we propose an interfacial engineering strategy for designing a class of strongly coupled hybrid materials as highly active electrocatalysts for catalytic N2 fixation. X-ray absorption near-edge spectroscopy (XANES) spectra confirm the successful construction of strong bridging bonds (Co-N/S-C) at the interface between CoS x nanoparticles and NS-G (nitrogen- and sulfur-doped reduced graphene). These bridging bonds can accelerate the reaction kinetics by acting as an electron transport channel, enabling electrocatalytic NRR at a low overpotential. As expected, CoS2/NS-G hybrids show superior NRR activity with a high NH3 Faradaic efficiency of 25.9% at -0.05 V versus reversible hydrogen electrode (RHE). Moreover, this strategy is general and can be extended to a series of other strongly coupled metal sulfide hybrids. This work provides an approach to design advanced materials for ammonia production.
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Exploitation of highly active and cost-effective electrode materials for the design of new types of renewable energy storage and conversion systems has been tremendously stimulated by the higher attention being paid to global energy security and invention of alternative clean sustainable energy technologies. Low-dimensional solid materials with special atomic and electronic structures are deemed desirable platforms for establishing clear relationships between surface/interface structure characteristics and electrocatalytic activity, representing enormous potential in the pursuit of high-performance electrocatalysts. Recent achievements revealed that surface and interfacial atomic engineering is capable of achieving novel physical and chemical properties as well as superior synergistic effects in inorganic low-dimensional nanomaterials for electrocatalysis. Compared to bulk counterparts, the electronic structure in the surface of inorganic low-dimensional nanomaterials is more sensitive to and can thus be regulated more easily by surface and interfacial modification strategies, resulting in greatly optimized electrocatalytic performance. In this Account, we focus on recent progress in surface and interfacial modification strategies to efficaciously engineer the electrocatalytic performance of inorganic low-dimensional electrode materials. We summarize several important regulation strategies of dimensional confinement, incorporation, surface reconstruction, interface modulation, and defect engineering, which immensely optimize the spin configuration, electrical conductivity, catalytic active site exposure, and reaction energy barrier of inorganic electrode material. At dimensionally confined atomic-scale thickness, more surface-facet atoms are exposed as active sites, which provide an ideal platform for applying surface incorporation and defect engineering, subsequently producing more catalytic active sites and better adsorption free energy for the improvement of catalytic activity. Moreover, regulation of the interfacial character of electrode materials, such as the surface strain, contact area, and bridged bonds, can optimize the electron transfer capacity and reaction kinetics process. On the other hand, once exposed to a strong alkaline solution under oxidizing potentials, the real active layer of electrode materials (such as transition-metal sulfides, nitrides, and phosphides) could be activated by a surface reconstruction strategy, realizing a unique core-shell structure with a highly conductive electron transfer channel inside and highly active catalytic sites outside for electrocatalysis. Based on these points of view, focusing on inorganic low-dimensional electrode materials, the proper choice of surface and interfacial modification strategies would effectively modulate their electrocatalytic activity, realizing unlimited potential applications in promising areas of electrocatalytic water splitting, rechargeable metal batteries, and fuel cells. Overall, we anticipate that surface and interfacial regulation approaches can provide a new understanding of the design of inorganic electrode materials, facilitating the rapid promotion of electrocatalytic performance in electrode materials for electrocatalysis.
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Perovskites are prototype electrocatalyts benefiting from their high terrestrial availability and high stability. Electronic state regulation plays a key role in promising higher electrocatalytic efficiencies. Herein, we highlighted a vibronic superexchange in double perovskite to synergistically optimize eg electron filling state and increase the formation of active species on the surface of catalysts. Vibronic superexchange of Ni3+-O-Mn3+ in La2NiMnO6 nanoparticles brings the optimal eg electron filling state of Mn and Ni ions toward unity. Moreover, a vibronic superexchange interaction of Ni3+-O-Mn3+ induces strong Jahn-Teller distortion of MnO6 and NiO6 octahedra, elongating metal-O bonds, which helps to form the active species of Mn/Ni hydroxide/oxide on the surface of catalysts. Surprisingly, La2NiMnO6 nanoparticles exhibit superior oxygen evolution reaction (OER) catalytic performance with higher current density and lower Tafel slope than its bulk counterpart. Our finding will be a promising pathway to develop advanced precious-metal-free catalysts.
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Fluorine-anion surface engineering has now been used to activate catalytic active species, representing a completely new way of reconstruction toward oxygen evolution reaction (OER) active species. The electronegativity of the fluorine anion is the strongest so that it will be much easier to form weak metal-fluorine bonds with stronger ionicity, contributing to the dynamic migration of fluorine anions and finally enriching on the surface of both cobalt-based oxide/oxyhydroxide. Surface enrichment of fluorine anions endows more hydrophilic surface character for accelerating the key process of oxygen-related intermediate adsorption. Combining with an obviously improved electron transfer capacity, the F-CoOOH/NF catalyst exhibits a greatly enhanced OER activity (270â mV at 10â mA cm-2 ) and reaction kinetics (54â mV dec-1 ) in alkaline medium. Surface anion engineering introduces a new concept for rational design advanced OER catalysts for energy conversion system.
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The electrocatalyzed oxygen reduction and evolution reactions (ORR and OER, respectively) are the core components of many energy conversion systems, including water splitting, fuel cells, and metal-air batteries. Rational design of highly efficient non-noble materials as bifunctional ORR/OER electrocatalysts is of great importance for large-scale practical applications. A new strongly coupled hybrid material is presented, which comprises CoOx nanoparticles rich in oxygen vacancies grown on B,N-decorated graphene (CoOx NPs/BNG) and operates as an efficient bifunctional OER/ORR electrocatalyst. Advanced spectroscopic techniques were used to confirm formation of abundant oxygen vacancies and strong Co-N-C bridging bonds within the CoOx NPs/BNG hybrid. Surprisingly, the CoOx NPs/BNG hybrid electrocatalyst is highly efficient for the OER with a low overpotential and Tafel slope, and is active in the ORR with a positive half-wave potential and high limiting current density in alkaline medium.
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Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-Nx species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-Nx species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.
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Developing highly active catalysts for the oxygen evolution reaction (OER) is of paramount importance for designing various renewable energy storage and conversion devices. Herein, we report the synthesis of a category of Co-Pi analogue, namely cobalt-based borate (Co-Bi ) ultrathin nanosheets/graphene hybrid by a room-temperature synthesis approach. Benefiting from the high surface active sites exposure yield, enhanced electron transfer capacity, and strong synergetic coupled effect, this Co-Bi NS/G hybrid shows high catalytic activity with current density of 10â mA cm(-2) at overpotential of 290â mV and Tafel slope of 53â mV dec(-1) in alkaline medium. Moreover, Co-Bi NS/G electrocatalysts also exhibit promising performance under neutral conditions, with a low onset potential of 235â mV and high current density of 14.4â mA cm(-2) at 1.8â V, which is the best OER performance among well-developed Co-based OER electrocatalysts to date. Our finding paves a way to develop highly active OER electrocatalysts.
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Inorganic nanowire arrays hold great promise for next-generation energy storage and conversion devices. Understanding the growth mechanism of nanowire arrays is of considerable interest for expanding the range of applications. Herein, we report the solution-liquid-solid (SLS) synthesis of hexagonal nickel selenide nanowires by using a nonmetal molecular crystal (selenium) as catalyst, which successfully brings SLS into the realm of conventional low-temperature solution synthesis. As a proof-of-concept application, the NiSe nanowire array was used as a catalyst for electrochemical water oxidation. This approach offers a new possibility to design arrays of inorganic nanowires.
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Exploring efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts is of great importance for various electrochemical energy storage and conversion technologies. Ni-based electrocatalysts have been actively pursued because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Ni-based electrocatalysts has been intrinsically limited due to their low electrical conductivity and poor active site exposure yield. Herein, we report metallic Ni3N nanosheets as an efficient OER electrocatalyst for the first time. The first-principles calculations and electrical transport property measurements unravel that the Ni3N is intrinsically metallic, and the carrier concentration can be remarkably improved with dimensional confinement. The EXAFS spectra provide solid evidence that the Ni3N nanosheets have disordered structure resultant of dimensional reduction, which then could provide more active sites for OER. Benefiting from enhanced electrical conductivity with metallic behavior and atomically disordered structure, the Ni3N nanosheets realize intrinsically improved OER activity compared with bulk Ni3N and NiO nanosheets. Our finding suggests that metallic nitride nanosheets could serve as a new group of OER electrocatalysts with excellent property.
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Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co4N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co4N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257â mV at a current density of 10â mA cm(-2), and a low Tafel slope of 44â mV dec(-1) in an alkaline medium, which is the best OER performance among reported Co-based electrocatalysts to date. Moreover, in-depth mechanistic investigations demonstrate the active phases are the metallic Co4N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high-efficiency OER electrocatalysts.
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Coupling hydrazine oxidation reaction (HzOR) with hydrogen evolution reaction (HER) has been widely concerned for high efficiency of green hydrogen preparation with low energy consumption. However, the lacking of bifunctional electrodes with ampere-level performance severely limits its industrialization. Herein, we put forward an efficient active site anchored strategy for MnCo2O4 nanosheet arrays on nickel foam (NF) by introducing Pt species (denoted as Pt-MnCo2O4/NF), which is standing for excellent bifunctional electrodes. The Pt-MnCo2O4/NF delivers ultralow potentials of -195 mV and 350 mV at 1000 mA cm-2 as well as robust stability for HzOR and HER, respectively. The study of in-situ Raman and reaction kinetics reveal that the formation of key adsorbed *NH2 and *N2H4 intermediates and the rapidly oxidization of intermediates with a fast interfacial charge transfer on Pt-MnCo2O4/NF. Remarkably, the Pt-MnCo2O4/NF assembled two-electrode hydrazine assisted water electrolyzer realizes current density of 100 mA cm-2 and 1000 mA cm-2 at 0.16 V and 0.62 V with over 80 h stability. This work provides a promising way to design efficient electrodes for energy-saving H2 generation under ampere-level current density.
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A new metallic 2D material with high electrical conductivity (1×10(3) S m(-1)) consists of VSe2 ultrathin nanosheets with 4-8 Se-V-Se atomic layers. This is the first 2D transition-metal dichalcogenide with intrinsic room-temperature ferromagnetism. The nanosheets increase the charge-density-wave transition temperature to 135 K by dimensional reduction.
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Low-dimensional cobalt-based materials have proved to be one of the promising catalytic systems for oxygen-evolution reaction (OER). How to develop a facile and universal strategy for significantly improving their catalytic performance is of great significance, but still faces great challenges. Herein, a series of cobalt-based nanowires (CoS2, CoP, CoF2, and Co3O4) are synthesized and used as conceptual examples to explore the universality to enhance their OER catalytic activity. The FeOOH-modified cobalt-based electrocatalysts exhibit significantly improved OER catalytic performance compared to the pristine samples. Especially, the optimal CoS2@FeOOH material delivers the smallest overpotential of 260 mV at 100 mA cm-2, which outperforms most of the reported excellent materials. Notably, the CoP||CoP@FeOOH electrolyzer (1.63 V@30 mA cm-2) delivers higher performance than the CoS2||CoS2@FeOOH electrolyzer (1.72 V@30 mA cm-2) benefiting from the better HER catalytic activity of CoP. In addition, the post-characterizations confirm that the real catalytic structure of those electrocatalysts consists of a surface CoOOH@FeOOH catalytic layer and cobalt-based nanowire core. The Co-Fe catalytic layer provides more active centers for the adsorption and dissociation of water molecules as well as the formation of oxygen, while the nanowire core acts as an electron transport channel to realize better reaction kinetics. Our work not only develops a general strategy to enhance the catalytic activity but also provides new ideas for the facile design of other advanced catalytic materials.
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Electrochemical urea electrolysis has been regarded as a promising strategy to replace traditional water-splitting technology to achieve hydrogen fuel due to its cost savings and high energy efficiency. Designing efficient bifunctional electrocatalysts easily is important but still faces significant challenges. Herein, an interface engineering strategy is used to construct a hybrid material by coupling cobalt molybdate (CoMoO4) nanosheet arrays with phosphorus-modified nickel (P-Ni) particles on copper foam (P-Ni@CoMoO4/CF) through the hydrothermal and in-situ electrodeposition process. Benefiting from the abundant catalytic active sites, low charge transfer resistance, and synergistic coupling effect, the optimal P-Ni@CoMoO4/CF electrocatalyst presents a superior bifunctional activity for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). In detail, a small overpotential of 125 mV and a low potential of 1.36 V is required to attain the current density of 100 mA cm-2 for HER and UOR, respectively. In the process of urea electrolysis, the P-Ni@CoMoO4/CF-based electrolyzer provides a current density of 100 mA cm-2 with an overall voltage of 1.50 V, about 170 mV less than that in a traditional water electrolyzer. The high performance of P-Ni@CoMoO4/CF outperforms many recently reported electrodes, suggesting its promising application in energy-saving hydrogen production. Our work proposes a novel idea for the rational design and exploitation of low-cost and robust bifunctional electrodes for electrocatalysis.
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Developing high-performance and low-cost self-supporting electrodes as pH-universal electrocatalysts for the hydrogen-evolution reaction (HER) and realizing high-quality hydrogen production at a high current density are highly desirable, but are hugely challenging. We created a self-supporting electrode with a coupled hierarchical heterostructure by simple electrodeposition followed by sulfurization. It comprised oxygen-deficient molybdenum oxide (MoO3-x) and cobalt phosphide (CoP) on nickel foam (NF), which represented a highly active pH-universal electrocatalyst for the HER at a high current density. Benefiting from a plethora of catalytic active sites, improved interfacial charge transfer, and strong electronic interaction, this type of MoO3-x@CoP/NF electrode delivered a superior catalytic performance. Overpotentials of only 100 mV, 135 mV, and 400 mV were needed to realize a high current density of 1 A cm-2 in alkaline, acid and neutral media, respectively, which were superior to those of most other well-developed materials based on non-noble metals. Our experimental work demonstrates the synergistic advantages of a MoO3-x@CoP heterostructure for improving the intrinsic catalytic performance but also paves a new path for the rational design of advanced electrodes for hydrogen generation in a wide range of pH conditions.
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Rational design of efficient electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct self-supported Co3 N nanowire arrays with different Mo doping contents by hydrothermal and nitridation processes that serve as robust electrocatalysts for overall water splitting. The optimal Co3 N-Mo0.2 /Ni foam (NF) electrode delivers a low overpotential of 97â mV at a current density of 50â mA cm-2 as well as a highly stable hydrogen evolution reaction (HER). Density functional theory (DFT) calculations prove that Mo doping can effectively modulate the electronic structure and surface adsorption energies of H2 O and hydrogen intermediates on Co3 N, leading to improved reaction kinetics with high catalytic activity. Further modification with FeOOH species on the surface of Co3 N-Mo0.2 /NF improves the oxygen evolution reaction (OER) performance benefiting from the synergistic effect of dual Co-Fe catalytic centers. As a result, the Co3 N-Mo0.2 @FeOOH/NF catalysts display outstanding OER catalytic performance with a low overpotential of 250â mV at 50 1â mA cm-2 . The constructed Co3 N-Mo0.2 /NF||Co3 N-Mo0.2 @FeOOH/NF water electrolyzer exhibits a small voltage of 1.48â V to achieve a high current density of 50â mA cm-2 at 80 °C, which is superior to most of the reported electrocatalysts. This work provides a new approach to developing robust electrode materials for electrocatalytic water splitting.
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The hydrazine oxidation reaction (HzOR) is considered as a promising alternative process of the oxygen evolution reaction (OER) to realize more energy-efficient hydrogen generation. However, the lack of highly active bifunctional catalysts poses a huge challenge to this strategy. In this work, we report a novel and universal electrodeposition strategy to rationally synthesize a self-supporting electrode. The utilization of ammonium fluoride helps to modulate not only the morphology of CoP, but also the synchronous formation of an anion-modified structure, leading to an excellent bifunctional performance. The optimal F-CoP/CF exhibits small potentials of -90 mV and 41 mV at 1 A cm-2, high stability and low Tafel slopes of 28 mV dec-1 and 3.26 mV dec-1 for the HER and HzOR, respectively. The highly efficient and stable bifunctional activity of F-CoP/CF can be further confirmed in an anion-exchange membrane hydrazine-assisted water electrolyzer (0.49 V at 1 A cm-2). Utilizing the density functional theory calculations, the optimized adsorption energy of water molecules and hydrogen intermediates of the HER as well as the rate-determining step of the HzOR are demonstrated for the F-CoP.