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Developing high-performance catalysts for fuel cell catalysis is one of the most critical and challenging steps for the commercialization of fuel cell technology. Here one-dimensional trimetallic platinum-iron-cobalt nanosaws (Pt

Fe-N-C represents the most promising non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) in fuel cells, but often suffers from poor stability in acid due to the dissolution of metal sites and the poor oxidation resistance of carbon substrates. In this work, silicon-doped iron-nitrogen-carbon (Si/Fe-N-C) catalysts were developed by in situ silicon doping and metal-polymer coordination. It was found that Si doping could not only promote the density of Fe-N

Structurally ordered L10-PtM (M = Fe, Co, Ni, etc) intermetallic nanocrystals (iNCs), benefiting from the chemically ordered structure and higher stability, are one of the best electrocatalysts used for PEMFC. However, their practical development is greatly plagued by the challenge that high-temperature annealing (> 700 °C) has to be used for realizing disorder-order phase transition (DOPT) due to the high activation barrier (Ea), which always leads to severe particle sintering, morphology change, and makes it highly challenging for gram-scale preparation of desirable PtM iNCs. Here, we report a general low-melting-point metal induced bond strength weakening strategy to promote DOPT of PtM (M = Ni, Fe, Cu, Zn) alloy catalysts. We demonstrate that the introduction of Sn can reduce DOPT temperature to a record-low temperature (≤ 450 °C), which enables ten-gram-scale preparation of high-performance L10-PtM iNCs. X-ray spectroscopic studies, in-situ electron microscopy and theoretical calculations reveal that the Sn-facilitated DOPT mechanism at record-low temperature involves the weakened bond strength and reduced Ea via Sn doping, the formation and fast diffusion of low coordinated surface free atom, and subsequent L10 nucleation. Most importantly, the 15% Sn-doped L10-PtNi iNCs display outstanding performance in H2-air fuel cells with a high peak power density of 1.45 W cm-2 for Pt alloy catalysts and less than 25% activity loss after 30000 cycles at a quite low cathode Pt loading amount of 0.12 mg¬Pt cm-2, representing as one of the most efficient cathodic electrocatalyst for PEMFCs.

Lithium-sulfur (Li-S) batteries have been regarded as an important candidate for next-generation energy storage devices due to their low cost and high theoretical energy density. However, several f...

Ni-rich ternary layered oxides represent the most promising cathodes for lithium ion batteries (LIBs) due to their relatively large specific capacities and high energy/power densities. Unfortunately, their inherent chemical instability and surface side reactions during the charge/discharge processes lead to rapid capacity fading and poor cycling life, which seriously restrict their practical applications. Herein, we report a simple dual-modification strategy for preparing LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode materials by Li2SnO3 surface coating and Sn4+ gradient doping. The gradient Sn doping stabilizes the layered structure due to the strong Sn–O covalent bond and relieves the Li+/Ni2+ cation disorder by the partial oxidation of Ni2+ to Ni3+. Besides, the ionic and electronic conductive Li2SnO3 coating serves as a protective layer to eliminate the side reactions with electrolyte/air. In LIB testing, the dual-modified NCM622 cathode with 2% Sn delivers an enhanced cycling performance with 88.31% capacity retention after 100 cycles from 3.0 to 4.5 V at 1C compared to the bare NCM622. Meanwhile, the dual-modified NCM622 shows an improved reversible capacity of 136.2 mA h g−1 at 5C and enhanced electrode kinetics. The dual-modification strategy may enable a new approach to simultaneously relieve the interfacial instability and bulk structure degradation of Ni-rich cathode materials for high energy density LIBs.

The electrochemical CO2 reduction reaction (CO2RR) to form highly valued chemicals is a sustainable solution to address the environmental issues caused by excessive CO2 emissions. Generally, it is challenging to achieve high efficiency and selectivity simultaneously in the CO2RR due to multi-proton/electron transfer processes and complex reaction intermediates. Among the studied formulations, bimetallic catalysts have attracted significant attention with promising activity, selectivity, and stability. Engineering the atomic arrangement of bimetallic nanocatalysts is a promising strategy for the rational design of structures (intermetallic, core/shell, and phase-separated structures) to improve catalytic performance. This review summarizes the recent advances, challenges, and opportunities in developing bimetallic catalysts for the CO2RR. In particular, we firstly introduce the possible reaction pathways on bimetallic catalysts concerning the geometric and electronic properties of intermetallic, core/shell, and phase-separated structures at the atomic level. Then, we critically examine recent advances in crystalline structure engineering for bimetallic catalysts, aiming to establish the correlations between structures and catalytic properties. Finally, we provide a perspective on future research directions, emphasizing current challenges and opportunities.

Morphology and crystal facet controlled Cu2O nanocrystals (NCs) including cubic Cu2O (c-Cu2O) NCs with {100} facets, rhombic dodecahedral Cu2O (d-Cu2O) NCs with {110} facets, and concave octahedral...

The sluggish kinetics of lithium polysulfides (LiPS) transformation is recognized as the main obstacle against the practical applications of the lithium-sulfur (Li-S) battery. Inspired by molybdoenzymes in biological catalysis with stable Mo-S bonds, porous Mo-N-C nanosheets with atomically dispersed Mo-N2/C sites are developed as a S cathode to boost the LiPS adsorption and conversion for Li-S batteries. Thanks to its high intrinsic activity and the Mo-N2/C coordination structure, the rate capability and cycling stability of S/Mo-N-C are greatly improved compared with S/N-C due to the accelerated kinetics and suppressed shuttle effect. The S/Mo-N-C delivers a high reversible capacity of 743.9 mAh g-1 at 5 C rate and an extremely low capacity decay rate of 0.018% per cycle after 550 cycles at 2 C rate, outperforming most of the reported cathode materials. Density functional theory calculations suggest that the Mo-N2/C sites can bifunctionally lower the activation energy for Li2S4 to Li2S conversion and the decomposition barrier of Li2S, accounting for its inherently high activity toward LiPS transformation.

Atomic ordering engineering has been a promising strategy to improve the catalytic activity and stability of Pt-based alloy catalysts for the oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs). However, the synthesis of shape-controlled ordered nanocrystals, especially in a two-dimensional (2D) architecture, still remains a great challenge. Herein, 2D Pd2Sn nanosheets (NSs) with unique Pd–Sn ordering are developed as efficient ORR electrocatalysts for the first time. The ordered Pd2Sn NSs exhibit a mass activity of 2.5 A mgPd−1 at 0.9 ViR-freevs. the reversible hydrogen electrode and outstanding durability, much superior to that of their disordered counterparts, commercial Pt/C, and most of the reported Pd-based ORR catalysts. The outstanding activity and stability can be ascribed to the unique 2D defect-rich morphology, the thermodynamically stabilized intermetallic structure, and the optimized Pd–O binding due to Sn incorporation.

The development of highly efficient and durable water electrolysis catalysts plays an important role in the large-scale applications of hydrogen energy. In this work, protrusion-rich Cu@NiRu core@shell nanotubes are prepared by a facile wet chemistry method and used for catalyzing hydrogen evolution reaction (HER) in an alkaline environment. The protrusion-like RuNi alloy shells with accessible channels and abundant defects possess a large surface area and can optimize the surface electronic structure through the electron transfer from Ni to Ru. Moreover, the unique 1D hollow structure can effectively stabilize RuNi alloy shell through preventing the aggregation of nanoparticles. The synthesized catalyst can achieve a current density of 10 mA cm

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt-alloy with a Pt-skin. The synthesis of ultrasmall and ordered L10 -PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L10 -W-PtCo/C catalyst shows significant improvement in both initial activity and high-temperature stability. The L10 -W-PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt-Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.

Summary Well-defined metallic nanocrystals (NCs) have been explored as effective electrocatalysts for energy conversion and storage technologies (e.g., fuel cell or water splitting). It is commonly known that electrocatalytic performance can be enhanced by controlling composition, size, and surface morphology. In addition, precisely controlling the atomic arrangement inside NCs can improve performance, with their electronic structures being optimized via interfacial coupling. In this review, we summarize recent advances in atomic arrangement engineering approaches of metallic NCs. First, we introduce thermodynamic and kinetic principles to provide a basic understanding on atomic structure-property correlations. Then, several representative cases of atomic ordering and planar stacking engineering are highlighted for different electrocatalytic processes. Finally, perspectives on the roles of calculations, characterization, and practical applications are outlined.

The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water-splitting, metal–air batteries and CO2 electroreduction. Ni–Fe layered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes. Herein, we demonstrate that the introduction of elemental selenium (Se) with an optimized phase composition, i.e., monoclinic (m-) or trigonal (t-) Se, could effectively tailor the OER activity of NiFe-LDH. Compared to t-Se doped NiFe-LDH, the presence of hybrid m/t-Se could effectively tune the electronic states of Ni–O and Fe–O sites, promote the generation of OER-active γ-NiOOH, and inhibit Fe-migration during the OER process, thus enhancing the OER performance. The optimized Ni0.8Fe0.2-m/t-Se0.02-LDH catalyst exhibits extraordinarily high OER activity, with an overpotential of 200 mV at 10 mA cm−2, which is superior to those of IrO2 and most of the reported Se-based OER catalysts. The Ni0.8Fe0.2-m/t-Se0.02-LDH catalyst is further implemented as an anode for overall water splitting and demonstrates a low cell voltage of 1.50 V to achieve 10 mA cm−2.

In this work, monodisperse core/shell Cu/In2O3 nanoparticles (NPs) were developed to boost efficient and tunable syngas formation via electrochemical CO2 reduction for the first time. The efficiency and composition of syngas production on the developed carbon-supported Cu/In2O3 catalysts are highly dependent on the In2O3 shell thickness (0.4–1.5 nm). As a result, a wide H2/CO ratio (4/1 to 0.4/1) was achieved on the Cu/In2O3 catalysts by controlling the shell thickness and the applied potential (from −0.4 to −0.9 V vs reversible hydrogen electrode), with Faraday efficiency of syngas formation larger than 90%. Specifically, the best-performing Cu/In2O3 catalyst demonstrates remarkably large current densities under low overpotentials (4.6 and 12.7 mA/cm2 at −0.6 and −0.9 V, respectively), which are competitive with most of the reported systems for syngas formation. Mechanistic discussion implicates that the synergistic effect between lattice compression and Cu doping in the In2O3 shell may enhance the bindi...

Exploiting platinum-group-metal (PGM)-free electrocatalysts with remarkable activity and stability toward oxygen reduction reaction (ORR) is of significant importance to the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs). Here, a high-performance and anti-Fenton reaction cobalt-nitrogen-carbon (Co-N-C) catalyst is reported via employing double crosslinking (DC) hydrogel strategy, which consists of the chemical crosslinking between acrylic acid (AA) and acrylamide (AM) copolymerization and metal coordinated crosslinking between Co2+ and P(AA-AM) copolymer. The resultant DC hydrogel can benefit the Co2+ dispersion via chelated Co-N/O bonds and relieve metal agglomeration during the subsequent pyrolysis, resulting in the atomically dispersed Co-Nx/C active sites. By optimizing the ratio of AA/AM, the optimal P(AA-AM)(5-1)-Co-N catalyst exhibits a high content of nitrogen doping (12.36 at%) and specific surface area (1397 m2 g-1 ), significantly larger than that of the PAA-Co-N catalyst (10.59 at%/746 m2 g-1 ) derived from single crosslinking (SC) hydrogel. The electrochemical measurements reveal that P(AA-AM)(5-1)-Co-N possesses enhanced ORR activity (half-wave potential (E1/2 ) ≈0.820 V versus the reversible hydrogen electrode (RHE)) and stability (≈4 mV shift in E1/2 after 5000 potential cycles in 0.5 m H2 SO4 at 60 oC) relative to PAA-Co-N, which is higher than most Co-N-C catalysts reported so far.

Ni-rich ternary layered oxides represent the most promising cathodes for lithium ion batteries (LIBs) due to their relatively large specific capacities and high energy/power densities. Unfortunately, their inherent chemical instability and surface side reactions during the charge/discharge processes lead to rapid capacity fading and poor cycling life, which seriously restrict their practical applications. Herein, we report a simple dual-modification strategy for preparing LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode materials by Li2SnO3 surface coating and Sn4+ gradient doping. The gradient Sn doping stabilizes the layered structure due to the strong Sn-O covalent bond and relieves the Li+/Ni2+ cation disorder by the partial oxidation of Ni2+ to Ni3+. Besides, the ionic and electronic conductive Li2SnO3 coating serves as a protective layer to eliminate the side reactions with electrolyte/air. In LIB testing, the dual-modified NCM622 cathode with 2% Sn delivers an enhanced cycling performance with 88.31% capacity retention after 100 cycles from 3.0 to 4.5 V at 1C compared to the bare NCM622. Meanwhile, the dual-modified NCM622 shows an improved reversible capacity of 136.2 mA h g-1 at 5C and enhanced electrode kinetics. The dual-modification strategy may enable a new approach to simultaneously relieve the interfacial instability and bulk structure degradation of Ni-rich cathode materials for high energy density LIBs.

We report a facile route to fabricate free-standing NiFe hydroxides by corrosion engineering as high-performance bifunctional electrocatalysts for seawater splitting. Compared with H2SO4 and HNO3, HCl can promote the dissolution of Ni2+ from NiFe foam and the in situ formation of active NiFe hydroxides due to the strong interaction between Cl- and metal. In situ Raman spectroscopic characterization reveals that HCl corrosion induced NiFe hydroxides (HCl-c-NiFe) can generate oxygen evolution reaction (OER) active NiOOH species at a low potential of 1.4 V vs. reversible hydrogen electrode (RHE) and exhibits equally respectable activity for the hydrogen evolution reaction (HER). During a 1000 h test in an alkaline electrolyte or a 300 h test in an alkaline seawater electrolyte within a two-electrode system at 100 mA cm-2, the cell exhibits outstanding stability and high Cl- tolerance with a low working voltage of 1.62 V, outperforming benchmark Pt/IrO2 and most of the reported bifunctional catalysts.

The instinct scaling relations between the adsorption energies of key intermediates during OER lead to large overpotential for water/seawater splitting. Herein, we develop a new strategy to fabricate amorphous nickel-iron phosphides (NiFeP) with controllable morphologies as high-performance catalysts for overall seawater splitting. The ligand effect of P tunes the electronic states of the oxidized NiFe sites, thus breaks the scaling relations for OER and reduce the adsorption energy gap between HO* and HOO* from 3.08 eV to 2.62 eV. The NiFeP nanostructures exhibit extraordinarily low overpotentials of 129 mV for OER and 126 mV for HER at 100 mA cm−2 in simulated alkaline seawater, which outperform the best reported electrocatalysts. They could also be operated at 1.57 V with 100 mA cm−2 in a two-electrode electrolyzer and work for more than 500 h. Our work may provide a universal guidance for the design of highly active seawater splitting electrocatalysts.

The sluggish kinetics of lithium polysulfides (LiPS) transformation is recognized as the main obstacle against the practical applications of the lithium-sulfur (Li-S) battery. Inspired by molybdoenzymes in biological catalysis with stable Mo-S bonds, porous Mo-N-C nanosheets with atomically dispersed Mo-N

It is of great importance to develop highly efficient and stable Pt-free catalysts for electrochemical hydrogen generation from water electrolysis. Here, monodisperse 7.5 nm copper-doped ruthenium hollow nanoparticles (NPs) with abundant defects and amorphous/crystalline hetero-phases were prepared and employed as efficient hydrogen evolution electrocatalysts in alkaline electrolyte. Specifically, these NPs only require a low overpotential of 25 mV to achieve a current density of 10 mA cm-2 in 1.0 M KOH and show acceptable stability after 2000 potential cycles, which represents one of the best Ru-based electrocatalysts for hydrogen evolution. Mechanism analysis indicates that Cu incorporation can modify the electronic structure of Ru shell, thereby optimizing the energy barrier for water adsorption and dissociation processes or H adsorption/desorption. Cu doping paired with the defect-rich and highly open hollow structure of the NPs greatly enhances hydrogen evolution activity.

LiNi0.6Co0.2Mn0.2O2 has attracted considerable attention as a high-performance cathode material for lithium ion batteries due to its relatively high specific capacity and low cost. However, structural instability and side reactions at the surface, which occur during the charge/discharge process, largely limit its performance. Here, we introduce a nanoscale nitrogen-doped carbon layer at the surface of the LiNi0.6Co0.2Mn0.2O2 particles by using simple mechanical activation and pyrolysis methods. Systematic characterization indicates that a nitrogen-doped carbon layer approximately 16 nm thick is uniformly coated on the LiNi0.6Co0.2Mn0.2O2 particles. It has been proved beneficial to stabilize the layered structure of the LiNi0.6Co0.2Mn0.2O2 with less cation disorder and residual lithium at the surface. The nitrogen-doped carbon-coated LiNi0.6Co0.2Mn0.2O2 exhibited a capacity retention of 92% after 100 cycles from 3.0 to 4.5 V at 1 C, and a discharge capacity of 156 mAh g−1 at 5 C (78% of the capacity at 0.2 C), which is superior to the pristine LiNi0.6Co0.2Mn0.2O2 in this work and most other reported LiNi0.6Co0.2Mn0.2O2 cathodes. The improved electrochemical properties of the nitrogen-doped, carbon-coated cathode can be attributed to the higher degree of cation ordering, relieved side reactions between the cathode and electrolyte, and increased electronic conductivity.

With high theoretical specific density, low cost, and non-toxicity, Li-S batteries are regarded as a promising candidate for next-generation energy storage systems. However, the shuttling of soluble Li polysulfides (LiPSs) results in self-discharge and rapid capacity degradation. Herein, nitrogen-doped hierarchical porous carbon with embedded highly dispersed vanadium (v)-Nx sites (V-N-C) is developed as a high-performance Li-S battery cathode for the first time. The metal-organic polymer supramolecule structure formed by the electrostatic/hydrogen bond interaction of chitosan-VO3- strongly stabilizes V to generate a high density of V-Nx/C sites. During the discharge/charge process, the unique V-Nx/C active sites can serve as efficient catalysts to accelerate the redox kinetics of LiPSs, while the hierarchical porous carbon structure of V-N-C benefits the diffusion/transfer of Li+/e- and suppresses the shuttling of LiPSs. As a result, the S/V-N-C composite delivers a high specific capacity of 1111.2 mA h g-1 at 0.5C and maintains 573.6 mA h g-1 at 5C with a low capacity decay rate of 0.087% per cycle (over 500 cycles at 1C). The rate performance of the developed V-N-C cathode in Li-S batteries is superior to that of most of the reported M-N-C and carbon material/metal compound composite electrodes.

Understanding CO2 reduction reaction (CO2RR) and developing robust catalysts for selective CO2RR is key to closing carbon cycle and to achieving energy sustainability with desired environmental remediation. Electrochemical CO2RR on a catalyst surface is an attractive method to realize high reaction activity and selectivity under mild reaction conditions. Among various catalysts studied thus far, metallic Cu-based nanocatalysts have demonstrated to be promising for selective CO2RR to HCOOH, CO or, more importantly, to CH4, C2H4 and C2H6 with relatively high efficiency. This review summarizes recent progresses made on these Cu-based nanocatalysts for CO2RR, including fundamental of electrochemical CO2RR, representative approaches to Cu-based nanocatalysts via nanoporous structure, nanoparticle size, composition, surface, support and morphology controls. The review should offer readers some important insights on Cu-catalyzed CO2RR, and will further help readers in their efforts to design and develop robust catalysts for active and selective CO2RR.

Tin selenide (SnSe) has been explored as a promising anode material for sodium ion batteries (SIBs) but its electrochemical performance is strictly limited by the large volume variation during charge/discharge process and relatively low electronic conductivity. In this work, hierarchical Cu doped SnSe nanoclusters were prepared by a cost-efficient and nontoxic method and demonstrated as a high-performance anode for SIBs. Under optimized Cu doping degree (10 wt% Cu), the developed Cu-SnSe anode exhibits excellent rate performance with a high capacity of 330 mAh/g at 20 A/g and outstanding stability with a capacity of 304 mAh/g after 1000 cycles at 5 A/g (0.1–3.0 V vs. Na/Na+). The enhanced electronic conductivity, facilitated sodiation/desodiation process, and relieved volume change during cycling in Cu doped SnSe benefited from Cu doping and the unique hierarchical structure should account for its extraordinary sodiun storage performance.

The slow kinetics of oxygen reduction reaction (ORR) occurring at the cathode of a proton exchange membrane fuel cell require the presence of an electrocatalyst to reduce overpotential. MPt alloy nanocrystals (NCs) have been investigated over the last decade as efficient catalysts for ORR and recent studies have shown that structurally-ordered MPt NCs, i.e., intermetallic NCs (iNCs), are more active and exhibit enhanced stability compared with the corresponding randomly alloyed analogues. This mini-review highlights the recent progress in iNC catalyst development for ORR with emphasis on correlating the synthesis-structure-activity relationship. Perspectives and possible research directions to enhance MPt iNC catalytic performance are also proposed.

An effective and universal strategy is developed to enhance the stability of the non-noble-metal M-Nx /C catalyst in proton exchange membrane fuel cells (PEMFCs) by improving the bonding strength between metal ions and chelating polymers, i.e., poly(acrylic acid) (PAA) homopolymer and poly(acrylic acid-maleic acid) (P(AA-MA)) copolymer with different AA/MA ratios. Mossbauer spectroscopy and X-ray absorption spectroscopy (XAS) reveal that the optimal P(AA-MA)-Fe-N catalyst with a higher Fe3+ -polymer binding constant possesses longer FeN bonds and exclusive Fe-N4 /C moiety compared to PAA-Fe-N, which consists of ≈15% low-coordinated Fe-N2 /N3 structures. The optimized P(AA-MA)-Fe-N catalyst exhibits outstanding ORR activity and stability in both half-cell and PEMFC cathodes, with the retention rate of current density approaching 100% for the first 37 h at 0.55 V in an H2 -air fuel cell. Density functional theory (DFT) calculations suggest that the Fe-N4 /C site could optimize the difference between the adsorption energy of the Fe atoms on the support (Ead ) and the bulk cohesive energy (Ecoh ) relative to Fe-N2 /N3 moieties, thereby strongly stabilizing Fe centers against demetalation.

Pd is a catalyst for electrochemical CO2 reduction to CO but often disturbed by H2 and formate formation at low overpotentials due to its strong affinity to H atoms. Herein, guided by density functional theory (DFT) calculations, Bi-Pd single atom alloy (SAA) nanodendrites (NDs) with Bi atomically dispersed in Pd matrices have been developed for efficient CO2 reduction to CO. The Faradic efficiencies (FEs) of CO on the Bi6Pd94-SAA ND catalyst reach 90.5 % and 91.8 % in H-type and gas diffusion flow cells with overpotentials of only 290 and 200 mV, respectively, which are among the best of the reported Pd-based electrocatalysts. The greatly enhanced CO formation on the Bi6Pd94-SAA NDs can be attributed to the increased reaction barriers for H2 formation due to a lower H coverage resulted from Bi doping, and the decreased free energy for *COOH generation which is a key intermediate for CO production.

Transition metal phosphides are often studied as hydrogen evolution reaction cathode catalysts, but scarcely as oxygen evolution reaction (OER) anode catalysts for water oxidation. Herein, we report a new amorphous Co0.63Fe0.21P0.16 OER catalyst, which was prepared through a one-step solvothermal process. This catalyst exhibits extraordinary OER catalytic activity in alkaline media and is superior to the state of the art IrO2 in 1.0 M KOH, capable of yielding a current density of 10 mA cm−2 at an overpotential of only 217 mV. This newly achieved high activity outperforms most reported transition metal phosphide catalysts. During the OER, the surface layers of the Co0.63Fe0.21P0.16 nanospheres (200–500 nm) are oxidized, which show the typical Tafel slope of oxides around 40 mV dec−1. The in situ formation of surface Co oxides in the catalysts during the OER along with an optimal doping of Fe are found to be crucial for their remarkable activity. In particular, the metal-rich amorphous phosphide cores, i.e., substrates, probably contribute to OER performance of the catalysts due to their high electrical conductivity. This new type of surface oxidized amorphous transition metal phosphide would provide a new pathway for the design of high-performance OER electrocatalysts.

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt-alloy with a Pt-skin. The synthesis of ultrasmall and ordered L1

Lithium-sulfur (Li–S) battery has aroused intensive attention due to its intrinsicly high capacity and energy density. However, the sluggish kinetics of lithium polysulfide (LiPS) redox conversion and shuttle effect severely damage the sulfur utilization, rate performance, and cycling stability of Li–S batteries. In this work, we report that Ru-doping induced phase transformation from MoP to Mo4P3 (Ru–Mo4P3) could significantly facilitate the electrocatalytic conversion of LiPS. When Ru–Mo4P3 nanoparticles (NPs) are decorated on hollow carbon spheres (HCS), the S/HCS-Ru-Mo4P3 electrode delivers high reversible capacities of 1178 mAh g−1 and 660 mAh g−1 at 0.5C and 4C in Li–S battery, respectively. The rate performance of the developed S/HCS-Ru-Mo4P3 is among the best of the reported transition metal phosphide cathodes for Li–S batteries. When the S loading is as high as 6.6 mg cm−2, S/HCS-Ru-Mo4P3 retains a reversible areal capacity of 5.6 mAh cm−2 after 50 cycles, higher than that of the commercial Li-ion battery (4 mAh cm−2). The excellent Li–S battery performance can be attributed to the intrinsically active Ru–Mo4P3 phase combining with hollow carbon structure, which significantly facilitates the electrocatalytic conversion and entrapment of LiPS.

Li-S battery technology, with high theoretical capacity and energy density, has drawn much attention in recent years as a possible replacement for current Li-ion battery technologies. A major drawback of Li-S batteries is a severe capacity fading effect which, to a large extent, stems from the dissolution and diffusion of lithium polysulfides (LiPS) that are formed during both charge and discharge cycles. The self-discharge caused by the LiPS migration during the charge process (the so-called "shuttle effect") often leads to the capacity decay of Li-S batteries. Herein, hollow structured metal oxide (Co3O4, Mn2O3, and NiO) submicro-spheres are prepared by a novel method and employed as efficient LiPS immobilizers. These Li-S batteries, based on the developed metal oxide spheres, possess outstanding rate capability and cycling stability. The best performing S/C/Co3O4 electrode delivers excellent cycling stability with only a 0.066% capacity decay per cycle during 550 cycles. Moreover, its discharge capacity is as high as 428 mA h g-1 at a 3C rate which is far superior to that of bare S/C (115 mA h g-1) at 3C. The fast kinetics of the electrocatalytic conversion of LiPS on the developed Co3O4 electrode and its unique hollow structure are the key factors that lead to its outstanding performance as a Li-S battery cathode material.

A facile H2 O2 oxidation treatment to tune the properties of metal disulfides for oxygen evolution reaction (OER) activity enhancement is introduced. With this method, the degree of oxidation can be readily controlled and the effect of surface S residues in the resulted metal (oxy)hydroxides for the OER is revealed for the first time. The developed NiFe (oxy)hydroxide catalyst with residual S demonstrates an extraordinarily low OER overpotential of 190 mV at the current density of 10 mA cm-2 after coupling with carbon nanotubes, and outstanding performance in Zn-air battery tests. Theoretical calculation suggests that the surface S residues can significantly reduce the adsorption free energy difference between O* and OH* intermediates on the Fe sites, which should account for the high OER activity of NiFe (oxy)hydroxide catalysts. This work provides significant insight regarding the effect of surface heteroatom residues in OER electrocatalysis and offers a new strategy to design high-performance and cost-efficient OER catalysts.