Tailoring Zirconia Supported Intermetallic Platinum Alloy via Reactive Metal-Support Interactions for High-Performing Fuel Cells.

Developing efficient and anti-corrosive oxygen reduction reaction (ORR) catalysts is of great importance for the applications of proton exchange membrane fuel cells (PEMFCs). Herein, we report a novel approach to prepare metal oxides-supported intermetallic Pt alloy nanoparticles (NPs) via the reactive metal-support interaction (RMSI) as ORR catalysts, using Ni-doped cubic ZrO2 (Ni/ZrO2) supported L10-PtNi NPs as a proof of concept. Benefiting from the Ni migration during RMSI, the oxygen vacancy concentration in the support is increased, leading to an electron enrichment of Pt. The optimal L10-PtNi-Ni/ZrO2-RMSI catalyst achieves remarkably low mass activity (MA) loss (17.8%) after 400,000 accelerated durability test cycles in a half-cell and exceptional PEMFC performance (MA = 0.76 A mgPt-1 at 0.9 V, peak power density = 1.52/0.92 W cm-2 in H2-O2/-air, and 18.4% MA decay after 30,000 cycles), representing the best reported Pt-based ORR catalysts without carbon supports. Density functional theory (DFT) calculations reveal that L10-PtNi-Ni/ZrO2-RMSI requires a lower energetic barrier for ORR than L10-PtNi-Ni/ZrO2 (direct loading), which is ascribed to a decreased Bader charge transfer between Pt and *OH, and the improved stability of L10-PtNi-Ni/ZrO2-RMSI compared to L10-PtNi-C can be contributed to the increased adhesion energy and Ni vacancy formation energy within the PtNi alloy.

A sodium-ion-conducted asymmetric electrolyzer to lower the operation voltage for direct seawater electrolysis.

Hydrogen produced from neutral seawater electrolysis faces many challenges including high energy consumption, the corrosion/side reactions caused by Cl-, and the blockage of active sites by Ca2+/Mg2+ precipitates. Herein, we design a pH-asymmetric electrolyzer with a Na+ exchange membrane for direct seawater electrolysis, which can simultaneously prevent Cl- corrosion and Ca2+/Mg2+ precipitation and harvest the chemical potentials between the different electrolytes to reduce the required voltage. In-situ Raman spectroscopy and density functional theory calculations reveal that water dissociation can be promoted with a catalyst based on atomically dispersed Pt anchored to Ni-Fe-P nanowires with a reduced energy barrier (by 0.26 eV), thus accelerating the hydrogen evolution kinetics in seawater. Consequently, the asymmetric electrolyzer exhibits current densities of 10 mA cm-2 and 100 mA cm-2 at voltages of 1.31 V and 1.46 V, respectively. It can also reach 400 mA cm-2 at a low voltage of 1.66 V at 80 °C, corresponding to the electricity cost of US$1.36 per kg of H2 ($0.031/kW h for the electricity bill), lower than the United States Department of Energy 2025 target (US$1.4 per kg of H2).

Inducing Covalent Atomic Interaction in Intermetallic Pt Alloy Nanocatalysts for High-Performance Fuel Cells.

The harsh working environments of proton exchange membrane fuel cells (PEMFCs) pose huge challenges to the stability of Pt-based alloy catalysts. The widespread presence of metallic bonds with significantly delocalized electron distribution often lead to component segregation and rapid performance decay. Here we report L10 -Pt2 CuGa intermetallic nanoparticles with a unique covalent atomic interaction between Pt-Ga as high-performance PEMFC cathode catalysts. The L10 -Pt2 CuGa/C catalyst shows superb oxygen reduction reaction (ORR) activity and stability in fuel cell cathode (mass activity=0.57 A mgPt -1 at 0.9 V, peak power density=2.60/1.24 W cm-2 in H2 -O2 /air, 28 mV voltage loss at 0.8 A cm-2 after 30 000 cycles). Theoretical calculations reveal the optimized adsorption of oxygen intermediates via the formed biaxial strain on L10 -Pt2 CuGa surface, and the durability enhancement stems from the stronger Pt-M bonds than those in L11 -PtCu resulted from Pt-Ga covalent interactions.

Si Doping Enables Activity and Stability Enhancement on Atomically Dispersed Fe-Nx /C Electrocatalysts for Oxygen Reduction in Acid.

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-Nx /C active sites but also elevated the content of graphitic carbon through catalytic graphitization. The best-performing Si/Fe-N-C exhibited a half-wave potential of 0.817 V vs. reversible hydrogen electrode in 0.5 m H2 SO4 , outperforming that of undoped Fe-N-C and most of the reported Fe-N-C catalysts. It also exhibited significantly enhanced stability at elevated temperature (≥60 °C). This work provides a new way to develop non-precious metal ORR catalysts with improved activity and stability in acidic media.

Rationally Designing Efficient Electrocatalysts for Direct Seawater Splitting: Challenges, Achievements, and Promises.

Directly splitting seawater to produce hydrogen provides a promising pathway for energy and environmental sustainability. However, current seawater splitting faces many challenges because of the sluggish kinetics, the presence of impurities, membrane contamination, and the competitive chloride oxidation reaction at the anode, which makes it more difficult than freshwater splitting. This Review firstly introduces the basic mechanisms of the anode and cathode reactions during seawater splitting. We critically analyze the primary principles for designing catalysts for seawater splitting in terms of both the hydrogen and oxygen evolution reactions, including with noble metal, noble metal free, and metal-free catalysts. Strategies to design effective catalysts, such as active site population, synergistic effect regulation, and surface engineering, are discussed. Furthermore, promises, perspectives, and challenges in developing seawater splitting technologies for clean hydrogen generation are summarized.

Protrusion-Rich Cu@NiRu Core@shell Nanotubes for Efficient Alkaline Hydrogen Evolution Electrocatalysis.

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-2 in 1.0 m KOH with an overpotential of only 22 mV and show excellent stability after 5000 cycles, which is superior to most reported Ru-based catalysts. Density functional theory calculations illustrate that the weakened hydrogen adsorption on Ru sites induced by the alloying with Ni and active electron transfer between Ru and Ni/Cu are the keys to the much improved HER activity.

Effective Approaches for Designing Stable M-Nx /C Oxygen-Reduction Catalysts for Proton-Exchange-Membrane Fuel Cells.

The large-scale commercialization of proton-exchange-membrane fuel cells (PEMFCs) is extremely limited by their costly platinum-group metals (PGMs) catalysts, which are used for catalyzing the sluggish oxygen reduction reaction (ORR) kinetics at the cathode. Among the reported PGM-free catalysts so far, metal-nitrogen-carbon (M-Nx /C) catalysts hold a great potential to replace PGMs catalysts for the ORR due to their excellent initial activity and low cost. However, despite tremendous progress in this field in the past decade, their further applications are restricted by fast degradation under practical conditions. Herein, the theoretical fundamentals of the stability of the M-Nx /C catalysts are first introduced in terms of thermodynamics and kinetics. The primary degradation mechanisms of M-Nx /C catalysts and the corresponding mitigating strategies are discussed in detail. Finally, the current challenges and the prospects for designing highly stable M-Nx /C catalysts are outlined.

An effective dual-modification strategy to enhance the performance of LiNi0.6Co0.2Mn0.2O2 cathode for Li-ion batteries.

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.

Engineering the atomic arrangement of bimetallic catalysts for electrochemical CO2 reduction.

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.

Hydrochloric acid corrosion induced bifunctional free-standing NiFe hydroxide nanosheets towards high-performance alkaline seawater splitting.

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.

Bifunctional Atomically Dispersed Mo-N2/C Nanosheets Boost Lithium Sulfide Deposition/Decomposition for Stable Lithium-Sulfur Batteries.

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.

Core@shell Sb@Sb2O3 nanoparticles anchored on 3D nitrogen-doped carbon nanosheets as advanced anode materials for Li-ion batteries.

Antimony (Sb) based materials are regarded as promising anode materials for Li-ion batteries (LIBs) because of the high capacity, appropriate working potential, and earth abundance of antimony. However, the quick capacity decay due to the huge volume expansion during the cycling process seriously hinders its practical applications. Here, a nanocomposite of core@shell Sb@Sb2O3 particles anchored on 3D porous nitrogen-doped carbon (3DNC) nanosheets is synthesized by freeze drying and sintering in a reducing atmosphere. Structural characterization shows that the developed Sb@Sb2O3/3DNC electrode has a high surface area (839.8 m2 g-1) and unique Sb-O-C bonding, both contributing to the excellent electrochemical performance. The initial charge and discharge specific capacities of the Sb@ Sb2O3/3DNC anode in LIB tests are 1109 mA h g-1 and 1810 mA h g-1, respectively. Also, it shows a charge capacity of 696.9 mA h g-1 after 500 cycles at 1 A g-1 and 458 mA h g-1 at a current density of 5 A g-1. Moreover, the assembled Sb@Sb2O3/3DNC‖LiNi0.6Co0.2Mn0.2O2 battery exhibits a discharge capacity of more than 100 mA h g-1 after 25 cycles at 100 mA g-1. The synthetic method can be extended to obtain other nanocomposites of metal and carbon materials for high-performance energy storage devices.

Accelerated polysulfide conversion on hierarchical porous vanadium-nitrogen-carbon for advanced lithium-sulfur batteries.

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.

Elemental selenium enables enhanced water oxidation electrocatalysis of NiFe layered double hydroxides.

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.

Tungsten-Doped L10 -PtCo Ultrasmall Nanoparticles as a High-Performance Fuel Cell Cathode.

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.

Boosting Tunable Syngas Formation via Electrochemical CO2 Reduction on Cu/In2O3 Core/Shell Nanoparticles.

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 binding of *COOH on the Cu/In2O3 NP surface, leading to the enhanced CO generation relative to Cu and In2O3 catalysts. This report demonstrates a new strategy to realize efficient and tunable syngas formation via rationally designed core/shell catalyst configuration.

NiFe (Oxy) Hydroxides Derived from NiFe Disulfides as an Efficient Oxygen Evolution Catalyst for Rechargeable Zn-Air Batteries: The Effect of Surface S Residues.

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.

Efficient entrapment and catalytic conversion of lithium polysulfides on hollow metal oxide submicro-spheres as lithium-sulfur battery cathodes.

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.

Electrodeposited Mo3S13 Films from (NH4)2Mo3S13·2H2O for Electrocatalysis of Hydrogen Evolution Reaction.

Molybdenum sulfides are considered to be one kind of the promising candidates as cheap and efficient electrocatalysts for hydrogen evolution reaction (HER). But this is still a gap on electrocatalytic performance toward Pt. To further enhance electrocatalytic activity of molybdenum sulfides, in this work, we prepared Mo3S13 films with high ratio of sulfur to molybdenum by electrodeposition. The Mo3S13 films exhibit highly efficient electrocatalytic activity for HER and achieve a current density of 10 mA/cm2 at an overpotential of 200 mV with an onset potential of 130 mV vs RHE and a Tafel slope of 37 mV/dec, which is superior to other reported MoS2 films. The highly electrocatalytic activity is attributed to high percentage of bridging S22- and apical S2- as well as good conductivity. This study provides an avenue for designing new molybdenum sulfides electrocatalysts.

Tuning Sn-Catalysis for Electrochemical Reduction of CO2 to CO via the Core/Shell Cu/SnO2 Structure.

Tin (Sn) is known to be a good catalyst for electrochemical reduction of CO2 to formate in 0.5 M KHCO3. But when a thin layer of SnO2 is coated over Cu nanoparticles, the reduction becomes Sn-thickness dependent: the thicker (1.8 nm) shell shows Sn-like activity to generate formate whereas the thinner (0.8 nm) shell is selective to the formation of CO with the conversion Faradaic efficiency (FE) reaching 93% at -0.7 V (vs reversible hydrogen electrode (RHE)). Theoretical calculations suggest that the 0.8 nm SnO2 shell likely alloys with trace of Cu, causing the SnO2 lattice to be uniaxially compressed and favors the production of CO over formate. The report demonstrates a new strategy to tune NP catalyst selectivity for the electrochemical reduction of CO2 via the tunable core/shell structure.