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Most copper current collectors for commercial lithium-ion batteries (LIBs) are smooth copper foils, which cannot form a stable and effective combination with electrode slurry. They are likely to deform or fall off after long-term operation, resulting in a sharp decline in battery performance. What is worse is that this condition inevitably causes internal short circuits and thus brings about security risks. In this study, a process route of fabricating the functional surface structures on the surface of a copper collector for LIBs by twice-crisscross micro-plowing (TCMP) is proposed, which provides a new idea and an efficient method to solve the above problems from the perspective of manufacturing. The finite element simulation of TCMP combined with the cutting force test and morphological characterization is conducted to verify the forming mechanism of the surface structures on a copper sheet and its relationship with the processing parameters. The influence of several key processing parameters on the surface characteristics of the copper sheet is comprehensively explored. A series of functions is tested to obtain the optimal parameters for performance improvement of the current collector. Results show that the structured copper sheet with the cutting distance of 250 μm, cutting depth of 80 μm, and cutting crossing angle of 90° enables the best surface features of the current collector; the contact angle reaches 0°, the slurry retention rate is up to 89.2%, and the friction coefficient reaches 0.074. The battery using the as-prepared structured copper sheet as the current collector produces a specific capacity of 318.6 mAh/g after 50 cycles at a current density of 0.2 C, which is 132.7% higher than the one based on a smooth surface. The capacity reversibility of the sample with the new current collector is much better than that of the traditional samples, yielding a lower impedance.

Over the past several decades, the design of highly active and cost-effective catalysts and electrocatalyst has been the subject of intense research efforts.to However, there has been significantly less deliberate emphasis on rationally designing a catalyst system with a prolonged stability. A major obstacle comes from the ambiguity behind how catalyst degrades. Several degradation mechanisms have been proposed in literature, such as catalyst particles detachment of the substrate, metal atom dissolution, agglomeration, Ostwald ripening, or corrosion of the carbon support, but with a lack of systematic studies, the causal relations between degradation and these proposed mechanisms remain ambiguous. Here, we report a systematic study of a catalyst system comprising of small particles and single atoms of Pt sandwiched between graphene layers, GR/Pt/GR where Pt-specific catalysis occurs through “chemically transparent” outer Gr layer(s). Experimental and computational analyses unravel the degradation mechanism of the studied electrocatalyst architecture for oxygen reduction reaction in acidic medium. Catalyst suffers from atomic dissolution under ORR harsh acidic and oxidizing operation voltages. Single atoms trapped in point defects within the top graphene layer on their way hopping through towards the surface of GR/Pt/GR architecture. Trapping mechanism renders individual Pt atoms as single atom catalyst sites catalyzing ORR for thousands of cycles before washed away in the electrolyte. The GR/Pt/GR catalysts also compare favorably to state-of-the-art commercial Pt/C catalysts and demonstrates a rational design of a hybrid nanoarchitecture with a prolonged stability for thousands of operation cycles. The proposed Gr/metal/Gr architecture is not only applicable to other electrocatalytic reactions but can have several applications in sensors and biomedical fields.

Layer-structured Ca0.5CoO2 nanofibers were synthesized using an electrospinning process, and the mass activity and intrinsic activity are dramatically enhanced with iron doping.

Ammonia protonic ceramic fuel cells (PCFCs) have potential to be a highly efficient power source of high energy density. However, the inadequate catalytic activity of the existing anodes for utilization of ammonia greatly limits the performance of PCFCs. Here we report a Fe-modified state-of-the-art Ni cermet anode with greatly enhanced activity and durability toward utilization of ammonia. Cells with a Fe-decorated Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3 (Ni-BZCYYb) anode demonstrate an excellent performance, achieving peak power densities of 0.360, 0.723, 1.257, and 1.609 Wcm−2 at 550, 600, 650, and 700 oC, respectively, which are the highest performance of solid oxide fuel cells fueled on ammonia. In addition, the cells show an excellent durability when operated at a constant current density of 0.5 A cm−2 (or power density of ~0.435 Wcm−2) at 650 oC. The superior activity and durability of the Fe-modified Ni/BZCYYb anode is attributed to the alternation of NH3 adsorption strength and N2 desorption barrier heights, as confirmed by first-principles based mechanistic and microkinetic modeling. Our research provides a valuable guidance for the development of efficient electro-catalysts for ammonia PCFCs.

The development of anode materials with high-rate capability is critical to high-power lithium batteries. T-Nb2O5 has been widely reported to exhibit pseudocapacitive behavior and fast lithium storage capability. However, the other polymorphs of Nb2O5 prepared at higher temperatures have the potential to achieve even higher specific capacity and tap density than T-Nb2O5, offering higher volumetric power and energy density. Here, micrometer-sized H-Nb2O5 with rich Wadsley planar defects (denoted as d-H-Nb2O5) is designed for fast lithium storage. The performance of H-Nb2O5 with local rearrangements of [NbO6] octahedra blocks surpasses that of T-Nb2O5 in terms of specific capacity, rate capability, and stability. A wide range variation in valence of niobium ions upon lithiation was observed for defective H-Nb2O5 via operando X-ray absorption spectroscopy. Operando extended X-ray absorption fine structure and ex-situ Raman spectroscopy reveals a large and reversible distortion of the structure in the two-phase region. Computation and ex-situ X-ray diffraction analysis reveals that the shear structure expands along major lithium diffusion pathways and contracts in the direction perpendicular to the shear plane. Planar defects relieve strain through perpendicular arrangements of blocks, minimizing volume change and enhancing structural stability. In addition, strong Li adsorption on planar defects enlarges intercalation capacity. Different from nanostructure engineering, our strategy to modify the planar defects in the bulk phase can effectively improve the intrinsic property. The findings in this work offer new insights into designing fast Li-ion storage materials in micrometer sizes through defect engineering, and the strategy is applicable to the material discovery for other energy-related applications.

Utilizing ionic liquids (ILs) with low flammability as the precursor component for a gel polymer electrolyte is a smart strategy out of safety concerns. Solvate ionic liquids (SILs) consist of equimolar lithium bis(trifluoromethylsulfonyl)imide and tetraglyme, alleviating the main problems of high viscosity and low Li

Ti2Nb10O29 (TNO) is a suitable electrode for high-performance lithium-ion batteries and capacitors because of its large lithium storage capacity and high Li+ diffusivity. Currently, the rate or power capability of TNO-based systems is limited by the poor electronic conductivity of the material. Here we report our findings in design, synthesis, and characterization of a hierarchical N-rich carbon conductive layer wrapped TNO structure (TNO@NC) using a novel polypyrrole-chemical vapor deposition (PPy-CVD) process. It was found that carbon coating with PPy–carbon partially reduces Ti and Nb cations, forms TiN, and creates oxygen vacancies in the TNO@NC structure that further increase overall electronic and ionic conductivity. Various defect models and density functional theory (DFT) calculations are used to show how oxygen vacancies influence the electronic structure and Li-ion diffusion energy of the TNO@NC composite. The optimized TNO@NC sample shows notable rate capability in half-cells with a reversible capacity of 300 mAh g−1 at 1 C rate and maintains 211 mAh g−1 at a rate of 100 C, which is superior to that of most MxNbyOz materials. Full cell LiNi0.5Mn1.5O4 (LNMO)||TNO@NC lithium-ion batteries (LIB) and active carbon (AC)||TNO@NC hybrid lithium-ion capacitors (LIC) exhibited notable volumetric and gravimetric energy and power densities.

Reversible protonic ceramic electrochemical cells (R-PCECs) are a promising option for efficient and low-cost generation of electricity and hydrogen. Commercialization of R-PCECs, however, hinges o...

Fe-N-C single-atom catalysts (SACs) are emerging as a promising class of electrocatalysts for the oxygen reduction reaction (ORR) to replace Pt-based catalysts. However, due to the limited loading of Fe for SACs and the inaccessibility of internal active sites, only a small portion of the sites near the external surface are able to contribute to the ORR activity. Here, this work reports a metal-organic framework-derived Fe-N-C SAC with a hierarchically porous and concave nanoarchitecture prepared through a facile but effective strategy, which exhibits superior electrocatalytic ORR activity with a half-wave potential of 0.926 V (vs RHE) in alkaline media and 0.8 V (vs RHE) in acidic media while maintaining excellent stability. The superior ORR activity of the as-designed catalyst stems from the unique architecture, where the hierarchically porous architecture contains micropores as Fe SAC anchoring sites, meso-/macro-pores as accessible channels, and concave shell for increasing external surface area. The unique architecture has dramatically enhanced the utilization of previously blocked internal active sites, as confirmed by a high turnover frequency of 3.37 s

Highly efficient air electrodes are a key component of reversible fuel cells for energy storage and conversion; however, the development of efficient electrodes that are stable against water vapor remains a grand challenge. Here we report an air–electrode, composed of double perovskite material PrBa0.8Ca0.2Co2O5+δ (PBCC) backbone coated with nanoparticles (NPs) of BaCoO3−δ (BCO), that exhibits remarkable electrocatalytic activity for oxygen reduction reaction (ORR) while maintaining excellent tolerance to water vapor. When tested in a symmetrical cell exposed to wet air with 3 vol% H2O at 750 °C, the electrode shows an area specific resistance of ∼0.03 Ω cm2 in an extended period of time. The performance enhancement is attributed mainly to the electrocatalytic activity of the BCO NPs dispersed on the surface of the porous PBCC electrode. Moreover, in situ Raman spectroscopy is used to probe reaction intermediates (e.g., oxygen species) on electrode surfaces, as the electrochemical properties of the electrodes are characterized under the same conditions. The direct correlation between surface chemistry and electrochemical behavior of an electrode is vital to gaining insight into the mechanisms of the electrocatalytic processes in fuel cells and electrolysers.

While numerous oxygen electrocatalysts have been reported to enhance zinc-air battery (ZAB) performance, highly efficient electrocatalysts for the oxygen electrocatalysis need to be developed for broader commercialization of ZABs. Furthermore, areal (instead of volumetric) power density has been used to benchmark the performance of ZABs, often causing ambiguities or confusions. Here, we propose a methodology for evaluating the performance of a ZAB using the volumetric (rather than the areal) power density by taking into consideration the air electrode thickness. A nitrogen and sulfur co-doped metal-free oxygen reduction electrocatalyst (N-S-PC) is used as a model catalyst for this new metric. The electrocatalyst exhibited a half-wave potential of 0.88 V, which is similar to that of the Pt/C electrocatalyst (0.89 V) due to the effects of co-doping and a highly mesoporous structure. In addition, the use of volumetric activity allows fair comparison among different types of air electrodes. The N-S-PC-loaded air electrode demonstrated a higher peak power density (5 W cm-3) than the carbon felt or paper electrode in the ZAB test under the same testing conditions.

High-power energy storage devices are required for many emerging technologies. The rate capability of existing energy storage devices is inadequate to fulfill the requirements of fast charging and ...

The functional microporous layer, acting as a mass-transfer control medium with a rational structure and surface morphology as well as high electrical conductivity, significantly affects the performance of micro-direct methanol fuel cells (μDMFCs). Bioinspired by the architecture and multi-functional properties of mangrove roots, this study develops a simple and versatile strategy based on magnetron sputtering and chemical vapor deposition to fabricate a mangrove root-inspired carbon nanotube film (MR-CNTF) as the functional interface in μDMFCs. It has features such as ultralightweight, high porosity, and good electrical conductivity. During the synthesis process, an apex-growth model of CNTF is identified. The results indicate that the MR-CNTF used as a cathodic microporous layer can remarkably facilitate the oxygen transport and water management. Because of its multi-functional structure and excellent material characteristics, the passive μDMFC displays a peak power density of 14.9 mW cm

Reversible protonic ceramic electrochemical cells (R-PCECs) are ideally suited for efficient energy storage and conversion; however, one of the limiting factors to high performance is the poor stability and insufficient electrocatalytic activity for oxygen reduction and evolution of the air electrode exposed to the high concentration of steam. Here we report our findings in enhancing the electrochemical activity and durability of a perovskite-type air electrode, Ba0.9Co0.7Fe0.2Nb0.1O3-δ (BCFN), via a water-promoted surface restructuring process. Under properly-controlled operating conditions, the BCFN electrode is naturally restructured to an Nb-rich BCFN electrode covered with Nb-deficient BCFN nanoparticles. When used as the air electrode for a fuel-electrode-supported R-PCEC, good performances are demonstrated at 650 °C, achieving a peak power density of 1.70 W cm−2 in the fuel cell mode and a current density of 2.8 A cm−2 at 1.3 V in the electrolysis mode while maintaining reasonable Faradaic efficiencies and promising durability.

One of the key challenges that hinders broad commercialization of proton exchange membrane fuel cells is the high cost and inadequate performance of the catalysts for the oxygen reduction reaction (ORR). Here we report a composite ORR catalyst consisting of ordered intermetallic Pt-alloy nanoparticles attached to an N-doped carbon substrate with atomically dispersed Fe–N–C sites, demonstrating substantially enhanced catalytic activity and durability, achieving a half-wave potential of 0.923 V (vs. RHE) and negligible activity loss after 5000 cycles of an accelerated durability test. The composite catalyst is prepared by deposition of Pt nanoparticles on an N-doped carbon substrate with atomically dispersed Fe–N–C sites derived from a metal–organic framework and subsequent thermal treatment. The latter results in the formation of core–shell structured Pt-alloy nanoparticles with ordered intermetallic Pt3M (M = Fe and Zn) as the core and Pt atoms on the shell surface, which is beneficial to both the ORR activity and stability. The presence of Fe in the porous Fe–N–C substrate not only provides more active sites for the ORR but also effectively enhances the durability of the composite catalyst. The observed enhancement in performance is attributed mainly to the unique structure of the composite catalyst, as confirmed by experimental measurements and computational analyses. Furthermore, a fuel cell constructed using the as-developed ORR catalyst demonstrates a peak power density of 1.31 W cm−2. The strategy developed in this work is applicable to the development of composite catalysts for other electrocatalytic reactions.

Ge is considered a promising anode candidate for Li-ion batteries (LIBs); however, its practical applicability is hindered by the relatively slow Li-ion diffusion owing to the stiffness of the diamond-like structure. Inspired by little difference in electronegativity between Ge and P, we have designed a novel layered GeP anode for LIBs, which can be readily synthesized using a mechano-chemical method and a subsequent low-temperature annealing. In particular, GeP demonstrates the best performances among all Ge-based anode materials studied, attributed to its fast Li-ion diffusion compared to Ge counterpart and a unique Li-storage mechanism that involves intercalation, conversion, and alloying, as confirmed by XRD, TEM, XPS, and Raman spectroscopy. Specially, the initial layered crystal structure of GeP can be reconstructed during charging due to its low formation energy, thus offering remarkable reversibility during cycling. Further, this study implies that the formation energy of crystal structures could be an important parameter for strategic design of large-capacity anode materials for LIBs.

Ge-based anodes for Na-ion batteries (NIB) usually suffer from sluggish reaction kinetics, low initial Coulombic efficiency, poor reversible capacity, and short cycling life due mainly to its rigid diamond-like structure. Here we report our findings in characterization and application of a GeP anode with a flexible layered structure, synthesized by a simple mechanochemical method. When tested as the anode for NIBs, the GeP undergoes a self-healing Na-storage process that involves intercalation, conversion, and alloying, as co-revealed by ex-situ X-ray diffraction, HRTEM, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis. The peculiar self-healing phenomenon derives from its ultra-low formation energy (−0.19 eV) for reconstruction of the original layered structure, as confirmed by first-principle calculations. The low formation energy also enables the formation of chemical bonding between layered GeP and graphite, thus achieving unprecedented performances among all reported anode materials based on Group IVA- and Group VA elements. The structural design strategy guided by formation energy of desirable phases is also applicable to the development of other energy-storage materials.

Efficient electrocatalysts for oxygen reduction reaction (ORR) are critical to high-performance energy conversion and storage devices. As an important family of functional materials, alkaline earth...

Metal–organic frameworks (MOFs) hold great potential in the development of electrode materials for next-generation supercapacitors because of their versatile porous architectures. Here we report ou...

Organic polysulfanes are new type of attractive organosulfur electrode materials for next generation lithium-sulfur (Li-S) batteries because of their high sulfur content, low cost, and desirable energy density. However, conventional organic polysulfanes usually suffer from poor reversibility due to structure variation and irreversible conversion during cycling. Here we report the synthesis and characterization of a novel two-dimensional (2D) organic polysulfane with a unique molecular structure of polycyclic sulfur directly substituting the carboxyls of poly(acrylic acid) and grafted on the carbon chain through a coupling reaction with KI as a catalyst and KCl as a template. The obtained organic polysulfane nanosheets with 72 wt% sulfur (OPNS-72) exhibit high initial capacity of 891 mAh/g (based on whole composite), excellent cycling stability (0.014% capacity fading per cycle over 620 cycles at 1 C rate), superior rate capability (562 mAh/g at 10 C) and high mass loading of 9.7 mg/cm2. The remarkable cycling stability of the Li-S battery is attributed to the structural stability and highly reversible electrochemical reaction of the OPNS-72 electrode, as confirmed by the TEM image after cycling and operando Raman spectroscopy measurements under battery operating conditions. Further, the developed synthesis approach is applicable for the preparation of other organic polysulfane nanosheets as highly reversible electrodes for Li-S batteries.

Electrification of transportation has spurred the development of fast-charge energy storage devices. High-power lithium-ion batteries require electrode materials that can store lithium quickly and reversibly. Herein, the design and construction of a Nb

The development of low-cost, high-performance anode materials for Li-ion batteries (LIBs) is imperative to meet the ever-increasing demands for advanced power sources. Here we report our findings on the design, synthesis, and characterization of a new cation-disordered ZnSiP2 anode. When tested in LIBs, the disordered phase of ZnSiP2 demonstrates faster reaction kinetics and higher energy efficiency than the cation-ordered phase of ZnSiP2. The superior performance is attributed to the greater electronic and ionic conductivity and better tolerance against volume variation during cycling, as confirmed by theoretical calculations and experimental measurements. Moreover, the cation-disordered ZnSiP2/C composite exhibits excellent cycle stability and superior rate capability. The performance surpasses all reported multi-phase anodes studied. Further, a number of the cation-disordered phases in the Zn(Cu)–Si–P family with a wide range of cation ratios show similar performance, achieving large specific capacities and high first-cycle coulombic efficiency while maintaining desirable working potentials for enhanced safety.

Design and fabrication of supercapacitors (SCs) with high energy density, fast discharge rate, and long cycle life is of great importance; however, the performances of SCs depend critically on advances in materials development. Here we report the development of a high-performance electrode material composed of hierarchical, porous interlaced ultrathin Zn and Ni co-substituted Co carbonate hydroxides (ZnNiCo-CHs) nanosheets branched on N-doped carbon nanotube arrays (C@ZnNiCo-CHs), which were grown directly on a nickel foam current collector. The mesoporous features and large open spaces of the interlaced ultrathin ZnNiCo-CHs nanosheets provide more active sites for redox reactions and facilitate fast mass transport; the self-standing N-doped carbon nanotube arrays offer large surface area, promote fast electron transport, and enhance structure stability, resulting in outstanding rate capability and long-term stability. Density functional theory calculations suggest that the ZnNiCo-CHs nanosheets have low deprotonation energy, greatly facilitating the rate of redox reactions. Further, an asymmetric SC constructed from a C@ZnNiCo-CHs positive electrode and an N-, S-codoped rGOs negative electrode demonstrates a high energy density of 70.9 W h kg−1 at a power density of 966 W kg−1 while maintaining a capacity retention of 91% even after 20,000 cycles at 20 A g−1. The findings provide some important insight into rational design of transition metal compounds based materials for fast energy storage, which may be applicable to creating efficient and robust electrode materials for other energy-related devices.

The development of low-temperature and water-resistant heterogeneous catalysts without noble metals is vital in the effective treatment of atmospheric pollutants in practical application. Herein, we report that Cu(I)-O-Co interfaces of ultrafine CuOx on Co3O4 prepared by co-precipitation exhibit promising low-temperature activity and good water resistance. Experiment results together with density functional theory (DFT) calculations not only verify that Cu+ species are stabilized over Cu(I)-O-Co interfaces because of the strong interaction between Cu2O1 and Co3O4, but also demonstrate that the Cu(I)-O-Co interface facilitates oxygen species activation for promoting catalytic oxidation and reduces the accumulation of hydroxyl and bicarbonate species on the surface of CuOx/Co3O4. DFT calculations also reveal that the CO oxidation rate-limiting step via the dissociation pathway under dry conditions is the Co-OO-Cu species dissociation while the CO coupling with the adsorbed O2 becomes the rate determining step for CO oxidation through the direct pathway over Cu(I)-O-Co interface under humid conditions. Further, the CuOx/Co3O4 catalyst also exhibits superior and stable catalytic activity for toluene oxidation, comparable with partial supported noble metal catalysts (T90 = 190 °C). The present work gives a useful strategy for the rational design of low-temperature and water-resistant non-precious-based catalysts to be applicable in CO and toluene removal in practical applications.

The surface structure and material composition of current collectors have significant effects on the electrochemical performances of lithium-ion batteries (LIBs). In this work, a three-dimensional (3D) porous composite framework is applied as the anode current collector in LIBs. This unique 3D skeleton is composed of conductive carbon fiber/Cu core/shell fibrous structure. With an oxidation treatment upon the copper shell, the porous framework is assembled with CuO microspheres. Using mesocarbon microbead (MCMB) graphite powders as the active material, the cell with this 3D porous composite current collector shows an improved reversible discharge-charge capacity of 415 mAh g–1 at a current rate of 0.1 C after 50 cycles, which is much higher than that of the cell with a flat Cu foil (127 mAh g–1). It is demonstrated that this unique fibrous network of the 3D current collector coupled with the morphological effects of the CuO microspheres greatly improve the cell performance in terms of electrical conductivity, reversible capacity and cycling stability.

Solid oxide fuel cells (SOFCs) are potentially the most efficient technology for direct conversion of hydrocarbons to electricity. While their commercial viability is greatest at operating temperatures of 300–500 °C, it is extremely difficult to run SOFCs on methane at these temperatures, where oxygen reduction and C–H activation are notoriously sluggish. Here we report a robust SOFC that enabled direct utilization of nearly dry methane (with ~3.5% H2O) at 500 °C (achieving a peak power density of 0.37 W cm−2) with no evidence of coking after ~550 h operation. The cell consists of a PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofibre-based cathode and a BaZr0.1Ce0.7Y0.1Yb0.1O3–δ-based multifunctional anode coated with Ce0.90Ni0.05Ru0.05O2 (CNR) catalyst for reforming of CH4 to H2 and CO. The high activity and coking resistance of the CNR is attributed to a synergistic effect of cationic Ni and Ru sites anchored on the CNR surface, as confirmed by in situ/operando experiments and computations. Solid oxide fuel cells are most commercially viable when run at low temperatures, but this makes it challenging to achieve high performance with hydrocarbon fuels. Here the authors report a fuel cell running at 500 °C on nearly dry methane that incorporates a Ni–Ru–CeO2-based reforming catalyst, achieving high power densities and coking resistance.

The development of high-performance supercapacitors (SCs) often faces some contradictory and competing requirements such as excellent rate capability, long cycling life, and high energy density. One effective strategy is to explore electrode materials of high capacitance, electrode architectures of fast charge and mass transfer, and electrolytes of wide voltage window. Here we report a facile and readily scalable strategy to produce high-performance N-doped graphene with a high specific capacitance (∼390 F g −1 ). A symmetric SC device with a wide voltage window of 3.5 V is also successfully fabricated based on the N-doped graphene electrode. More importantly, the as-assembled symmetric SC delivers a high energy density of 55 Wh kg −1 at a power density of 1800 W kg −1 while maintaining superior cycling life (retaining 96.6% of the initial capacitance after 20,000 cycles). Even at a power density as high as 8800 W kg −1 , it still retains an energy density of 29 Wh kg −1 , higher than those of previously reported graphene-based symmetric SCs.

To minimize the impact of occasional fuel disruption or starvation during operation on fuel cell performance, an auxiliary power source is required, which increases the system complexity and cost. Here we report our findings in exploration of a bi-functional device that functions not only as a fuel cell to convert a chemical fuel to electricity but also as a battery to continue providing power when there is an interruption of fuel supply. The key component of this device is the bi-functional anode composed of Pt-WO3 nanowires. When hydrogen is continuously supplied to the fuel cell, it operates just like a normal fuel cell; when there is disruption of fuel supply, however, the device could deliver electric power for a longer period of time (additional 390 s) than a fuel cell with a normal Pt/C anode. Hydrogen inserts into the lattice of WO3 in the presence of Pt catalyst, as revealed by in situ Raman analysis, which can be released when there is a starvation of fuel. This work demonstrates the feasibility of a bi-functional fuel cell with energy storage capability, which may be applicable to other energy-related applications as well.

Summary This work demonstrates that a multi-phase catalyst coating (∼30 nm thick), composed of BaCoO 3−x (BCO) and PrCoO 3−x (PCO) nanoparticles (NPs) and a conformal PrBa 0.8 Ca 0.2 Co 2 O 5+δ (PBCC) thin film, has dramatically enhanced the rate of oxygen reduction reaction (ORR). When applied to a state-of-the-art La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) cathode in a solid oxide fuel cell (SOFC), the catalyst coating reduced the cathodic polarization resistance from 2.57 to 0.312 Ω cm 2 at 600°C. Oxygen molecules adsorb and dissociate rapidly on the NPs due to enriched surface oxygen vacancies and then quickly transport through the PBCC film, as confirmed by density functional theory-based computations. The synergistic combination of the distinctive properties of the two separate phases dramatically enhances the ORR kinetics, which is attractive not only for intermediate-temperature SOFCs but also for other types of energy conversion and storage systems, including electrolysis cells and membrane reactors for synthesis of clean fuels.

The energy density and operational life of lithium-ion batteries (LIBs) depend sensitively on the properties of electrode materials. Transition metal oxide based electrodes attract much attention because of their potential to offer high energy density. In this study, we report a binder-free composite anode composed of CuO nanosheets and multi-wall carbon nanotubes for LIBs. This composite anode is fabricated by a cost-effective electrophoretic deposition process followed by facile solution immersion. When tested in a LIB, this composite anode delivers a high reversible capacity of 540 mAh g−1 and maintains its capacity retention of above 78% after 50 cycles at a current density of 100 mA g−1, which is much higher than the CuO anode without carbon nanotubes. The high capacity, enhanced rate capability, low resistance, and increased operational life are attributed to the unique architecture of the hybrid electrode. The carbon nanotubes facilitate the electron transfer, enhance the structural stability of CuO nanosheets, and improve the adhesion of the CuO nanosheets to current collector. Such highly porous cross-linked network based on CuO nanosheets and multi-wall carbon nanotubes has great potential as a binder-free anode for high-performance LIBs.

Solid oxide cells (SOCs) are considered the most efficient system for reversible conversion between chemical and electrical energy, thus having potential to be an attractive technology for a sustainable energy future. To achieve high round-trip efficiency, highly efficient and durable air electrode materials are needed to minimize energy loss associated with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Here we report a bi-functional air electrode material, PrBa0.9Co1.96Nb0.04O5+δ, demonstrating outstanding electrochemical performance (e.g., achieving peak power densities of over 1.5 and 1 W cm−2, respectively, for Gd0.1Ce0.9O1.95 and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ based fuel cells at 600 °C) while maintaining excellent stability (e.g., having a degradation rate of 40 mV per 1,000 h for H2O electrolysis cells). The excellent property of the new electrode is attributed to the improved stability from Nb doping and the enhanced electrocatalytic activity from tuning Ba deficiency, as confirmed by experimental results and computational analysis.

Developing advanced architectures using a cost-effective synthesis strategy is still a challenge for wide-spread commercial application of Nb2O5 in high-power rechargeable lithium-ion batteries (LIBs). Here we report a new two-dimensional (2D) architecture composed of oxygen-vacancy-rich T-Nb2O5 on reduced graphene oxide nanosheet and carbon (2D Nb2O5-C-rGO), which is synthesized via a one-pot hydrolysis route followed by a heat-treatment. As an anode for LIBs, the 2D Nb2O5-C-rGO architecture shows excellent rate capability (achieving a capacity of 114 mAh g−1 at 100 C or 20 A g−1) and cycling stability (maintaining a capacity of 147 mAh g−1 at 5 C for 1,500 cycles and 107 mAh g−1 at 50 C for 5,000 cycles). Experimental investigations and density functional theory (DFT)-based calculations reveal that the outstanding Li+ storage performance of the 2D Nb2O5-C-rGO electrode is attributed to the enhanced electronic conductivity facilitated by the C-rGO electronic network and fast Li+ migration within small Nb2O5 grains enhanced by in-situ formed lattice oxygen vacancies, which alter the Nb d band structure and Li+ interaction. This work results in an anode with advanced architecture for fast Li+ storage and provides more insight into the energy storage mechanism in the Nb2O5-based carbonaceous composite electrodes.

One challenge facing the development of high-performance cathodes for solid oxide fuel cells (SOFC) is the fast degradation rate of cathodes due to poisoning by contaminants commonly encountered in ambient air such as CO2. Here we report a double perovskite PrBa0.8Ca0.2Co2O5+δ (PBCC) cathode with excellent ORR activity and remarkable CO2 tolerance under realistic operation conditions. When tested in a symmetrical cell in air with ∼1 vol% CO2 at 750 °C, the PBCC electrode shows an area specific resistance of ∼0.024 Ω cm2, which increases to 0.028 Ω cm2 after 1000 h operation. The degradation rate is ∼1/24 of that of the state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode under the same conditions. Impedance spectroscopy and in situ surface enhanced Raman spectroscopy analyses indicate that the surface of the PBCC electrode is much more active for oxygen exchange and more robust against CO2 than that of LSCF, as confirmed by density functional theory calculations. The fast ORR kinetics and excellent durability of PBCC in air with CO2 highlight the potential of PBCC as a highly promising material for devices involving oxygen electrochemistry such as solid oxide fuel cells, electrolysis cells, or gas separation membranes.