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Miniaturized microfluidic electrochemical energy devices can produce power without the need for a separator reducing a considerable amount of fabrication complications. Enzymatic biofuel cells, with glucose as a fuel, are capable of producing energy from biological fluids in the presence of biocatalysts. The tedious fabrication procedures can be avoided by making electrodes and microchannel using laser ablation technique on polyimide substrates. In this work, a microfluidic enzymatic biofuel cell (MEBFC) has been presented with CO2 laser-ablated microchannel and bioelectrodes using a mediatorless approach. Multiwalled carbon nanotubes (MWCNT) have been used as a promoter to enhance the electron transfer rate. The fabricated MEBFC shows good power performance supplying 4.7 μW/cm2 with a maximum open-circuit voltage of 260 mV.

Environmental degradation has promoted the exploitation of novel energy-storage devices. Electrochemical energy technologies, including supercapacitors and aqueous batteries, are highly desirable for energy storage applications. Among them, aqueous zinc-based batteries (AZBs) are highly valued because of their inherent safety and low cost. One class of emerging materials favorably employed in these devices are organic cathodes, featuring resource renewability, cost-effectiveness, and adjustable electrochemical properties via facile structural modification compared to the conventional inorganic cathodes. To date, various types of organic compounds have been developed and applied to AZIBs. This paper comprehensively reviews the mechanisms involved in organic electrode material reactions, highlighting the structural modifications, including morphological, molecular, functional group, crystal, and electronic structures, affecting the final device performance. Conclusively, the prospects of practical applications of zinc/organic aqueous battery are delineated.

In order to fully replace the traditional fossil energy supply system, the efficiency of electrochemical energy conversion and storage of new energy technology needs to be continuously improved to enhance its market competitiveness. The structural design of energy devices can achieve satisfactory energy conversion and storage performance. To achieve lightweight design, improve mechanical support, enhance electrochemical performance, and adapt to the special shape of the device, the structural energy devices develop very quickly. To help researchers analyze the development and get clear on developing trend, this review is prepared. This review summarizes the latest developments in structural energy devices, including special attention to fuel cells, lithium-ion batteries, lithium metal batteries, and supercapacitors. Finally, the existing problems of structural energy devices are discussed, and the current challenges and future opportunities are summarized and prospected. Structural energy devices can undoubtedly overcome the performance bottlenecks of traditional energy devices, break the limitations of existing materials and structures, and provide a guidance for the development of equipment with high performance, light weight and low cost in the future.

Design of advanced carbon nanomaterials with high-efficiency oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities is still imperative yet challenging for searching green and renewable energies. Herein, we synthesized ultrafine FeNi/(FeNi)9S8 nanoclusters encapsulated in nitrogen, sulfur-codoped graphitic carbon nanosheets (FeNi/(FeNi)9S8/N,S-CNS) by coordination regulated pyrolyzing the mixture of the metal precursors, dithizone and g-C3N4 at 800 °C. The as-prepared FeNi/(FeNi)9S8/N,S-CNS exhibited distinct electrocatalytic activity and stability for the ORR with positive onset (Eonset) and half-wave (E1/2) potentials (Eonset = 0.97 V; E1/2 = 0.86 V) and OER with the small overpotential (η = 283 mV) at 10 mA cm-2 in the alkaline media, outperforming commercial Pt/C and RuO2 catalysts. This research provides some constructive guidelines for preparing efficient, low-cost and stable nanocatalysts for electrochemical energy devices.

The retarded kinetics of oxygen evolution on electrodes is a bottleneck for electrochemical energy conversion and storage systems. NiFe-based electrocatalysts provide a cost-effective choice to confront this challenge. However, there is a lack of facile techniques for depositing compact catalytic films of high coverage and possessing a state-of-the-art performance, which is especially desired in photoelectrochemical (PEC) systems. Herein, we demonstrate a spray pyrolysis (SP) route to address this issue, featuring the kinetic selective preparation towards the desired catalytic-active material. Differing from reported SP protocols which only produce inactive oxides, this approach directly generates a unique composite film consisting of NiFe layered oxyhydroxides and amorphous oxides, exhibiting an overpotential as small as 255 mV (10 mA cm−2) and a turnover frequency of ∼0.4 s−1 per metal atom. By using such a facile protocol, the surface rate-limiting issue of BiVO4 photoanodes can be effectively resolved, resulting in a charge injection efficiency of over 90%. Considering this deposition directly start from simple nitrates but only takes several seconds to complete, we believe it can be developed as a widely applicable and welcomed functionalization technique for diverse electrochemical devices.

Efficient electrocatalytic reduction of CO2 to value-added chemicals and fuels is a promising technology for mitigating energy shortage and pollution issues yet highly relay on the development of high-performance electrocatalysts. Herein, we develop an effective strategy to fabricate carbonized wood membrane (CW) decorated with AuPd alloy nanoparticles with tunable composition (termed as AuPd@CW) as self-supported electrodes for efficient electrocatalytic CO2 reduction. The uniformly distributed AuPd nanoparticles on wood matrix are first achieved through the in-situ reduction of metal cations by the lignin content in wood. Subsequently, two-step carbonization was employed to promote the alloying of AuPd nanoparticles and the formation of CW. The AuPd@CW membrane electrode features an integrated macroscopic structure with numerous open and aligned channels for rapid electron transfer and mass diffusion and well-dispersed AuPd alloy nanoparticles as active sites for the CO2 reduction. The optimal Au95Pd5@CW electrode affords a high selectivity for CO2 electroreduction with a maximum CO faradaic efficiency (FECO) of 82% at an overpotential of 0.49 V, much higher than those obtained on Au@CW and Pd@CW electrodes. The CO current density and FECO remain relatively stable during a 12 h electrolysis reaction. In addition, density functional theory (DFT) calculations reveal that alloying Au with Pd enables a balance between the formation of intermediate COOH* and the desorption of CO on the surface of AuPd nanoparticles, thus enhancing the selectivity of CO production. This work offers an effective strategy for the fabrication of bimetallic alloys supported on wood-based carbon membrane as a practical electrode for electrochemical energy conversion.

Exploring cost-efficient electrocatalysts for oxygen evolution reaction (OER) is still a huge challenge in the electrochemical energy conversion technology. In this work, Gallium (Ga)-doped Ni3S2 nanosheet arrays grown on Ti3C2-MXene/nickel foam (Ga–Ni3S2/Ti3C2/NF) have been synthesized by a successive hydrothermal and sulfidization process. The Ga doping modulates the electronic structure of Ni3S2, so tuning the adsorption energies of oxygen intermediate (∗OOH). The Ga–Ni3S2/Ti3C2/NF delivers outstanding catalytic activities toward OER with an overpotential of 340 mV at 100 mA cm−2, and exhibits superior electrochemical durability. The excellent OER performance of Ga–Ni3S2/Ti3C2/NF can be ascribed to the 3D sheet arrays morphology and optimized electronic structure. Density functional theory (DFT) calculations also demonstrate that electronic disturbance attributed to Ga doping effectively improves the activity of Ni sites, leading to stronger binding strength of ∗OOH intermediate at Ni sites nearby Ga. This study provides insights into the fabrication of advanced electrocatalysts for application.

Electrochemical energy conversion technologies involving processes such as water splitting and O2/CO2 reduction, provide promising solutions for addressing global energy scarcity and minimizing adverse environmental impact. However, due to a lack of an in-depth understanding of the reaction mechanisms and the nature of the active sites, further advancement of these techniques has been limited by the development of efficient and robust catalysts. Therefore, in situ characterization of these electrocatalytic processes under working conditions is essential. In this review, recent applications of in situ Raman spectroscopy and X-ray absorption spectroscopy for various nano- and single-atom catalysts in energy-related reactions are summarized. Notable cases are highlighted, including the capture of oxygen-containing intermediate species formed during the reduction of oxygen and oxidation of hydrogen, and the detection of catalyst structural transformations occurring with the change in potential during the evolution of oxygen and reduction of CO2. Finally, the challenges and outlook for advancing in situ spectroscopic technologies to gain a deeper fundamental understanding of these energy-related electrocatalytic processes are discussed.

The development of nonprecious metal-based electrocatalysts for oxygen reduction reaction (ORR) is a central task in renewable electrochemical energy conversion and storage technologies. Iron-nitrogen doped carbon-based (Fe−N/C) materials are promising alternatives to Pt-based ORR electrocatalysts. Owing to large specific surface area and outstanding electrical conductivity, carbon black is an inborn support for electrocatalysts. Unfortunately, the direct incorporation of Fe−Nx moieties onto the surface of carbon black has not been realized to date. Herein, Fe−Nx moieties are directly incorporated onto the surface of carbon black through surface modification and the following Fe and N co-doping. The obtained Fe and N co-doped carbon back (Fe−N/CB) catalyst has very large specific surface area and abundant accessible Fe−Nx moieties. As a result, Fe−N/CB electrocatalyst exhibits a more positive half-wave potential (0.86 V) than Pt/C. The Fe−N/CB catalyst also displays better stability and methanol resistance than Pt/C. The Zn-air battery with Fe−N/CB as cathodic catalyst shows a maximum power density of 68 mW cm−2 and a specific capacity of 676 mAh gZn-1. Our finding provides a convenient and low-cost approach to fabricating efficient M−N/C-based catalysts and will be helpful to the development of renewable electrochemical energy conversion and storage technologies.

In past two decades electro chemical machining (ECM) and electric discharge machining (EDM) processes have been widely explored for machining of different grades of steel (including AISI 304). Although there is difference in material removal mechanism of EDM (localized heating and vaporization being thermal process) and ECM (ionic dissolution being electrochemical energy based process), yet the user needs broad data base for comparison and selection of particular process. But hitherto little has been reported on relative comparison of EDM and ECM processed AISI steel surface from surface roughness (Ra), surface hardness (HV) and morphological characteristics view point. This paper reports the comparison of AISI 304 steel machined surface by EDM and ECM. The comparison has been made after process optimization of EDM and ECM separately (using Taguchi approach). The results of study suggest that ECM is better process than EDM from Ra view point (3.10 µm for ECM and 6.41 µm for EDM) and porosity% view point, whereas from HV viewpoint no significant difference was observed.

Electrocatalysts play a crucial role in the development of renewable energy conversion and storage nanotechnologies. The unique advantages of heteroatom-doped porous carbon-supported single-atom electrocatalysts (SAC-HDPCs) are clear. These SAC-HDPCs exhibit outstanding activity, selectivity and stability due to their distinct electronic structure, satisfactory conductivity, controllable porosity and heteroatom-doping effect. Rapid and significant developments involving the synthesis, characterization, and structure-property-function relationship of SAC-HDPCs have been made in recent years. In this review, we describe recent research efforts involving advanced (in situ) characterization techniques, innovative synthetic strategies, and electrochemical energy conversion examples of SAC-HDPCs. The electrocatalytic performance of SAC-HDPCs is further considered at an atomic level, and the mechanisms underlying this performance are also discussed in detail. We expect that these analyses and deductions will be useful for the design of new materials and may help to establish a foundation for the design of future SAC-HDPCs.

Graphdiyne(GDY), which is composed of sp2-/sp-hybridized carbon atoms, has attracted increasing attention. In the structure of GDY, the existence of large triangular-like pores, well dispersed electron-rich cavities as well as a large π-conjugated structure endows GDY with a natural bandgap, fast electron/ion transport, and tunable electronic properties. These unique features make GDY competitive in areas of gas separation and capture, electronics, detectors, catalysts, biomedicine and therapy, and energy-related fields. Benefiting from the facile synthesis method, various GDY structures and GDY-based composites have been successfully prepared and show great potential in the practical application of energy storage and catalysis areas. Here, this review aims at providing a timely and comprehensive update on the preparation and application of GDY materials. The current development of GDY materials in various electrochemical fields especially in energy conversion, energy storage, and catalysis is mainly summarized. Moreover, the potential development prospects are also discussed.

As a crucial component of redox flow batteries (RFBs), porous electrode provides active sites for redox reaction to realize electrochemical energy conversion. The coupling reaction kinetics and mas...

Lithium-sulfur (Li-S) batteries constitute promising next-generation energy storage devices due to the ultrahigh theoretical energy density of 2600 Wh kg-1. However, the multiphase sulfur redox reactions with sophisticated homogeneous and heterogeneous electrochemical processes are sluggish in kinetics, thus requiring targeted and high-efficient electrocatalysts. Herein, a semi-immobilized molecular electrocatalyst is designed to tailor the characters of the sulfur redox reactions in working Li-S batteries. Specifically, porphyrin active sites are covalently grafted onto conductive and flexible polypyrrole linkers on graphene current collectors. The electrocatalyst with the semi-immobilized active sites exhibits homogeneous and heterogeneous functions simultaneously, performing enhanced redox kinetics and a regulated phase transition mode. The efficiency of the semi-immobilizing strategy is further verified in practical Li-S batteries that realize superior rate performances and long lifespan as well as a 343 Wh kg-1 high-energy-density Li-S pouch cell. This contribution not only proposes an efficient semi-immobilizing electrocatalyst design strategy to promote the Li-S battery performances but also inspires electrocatalyst development facing analogous multiphase electrochemical energy processes.

Pillararene/calixarene-based functional materials have garnered significant attention for their unique topological/chemical structures and physicochemical properties, and their extended applications in electrochemistry have given rise to a promising area of research. This review details current advance in developing electrochemical energy materials based on pillararene/calixarene systems from the viewpoint of both fundamental theoretical simulations and research on practical applications. First, we discuss the underlying mechanisms of applying pillararene/calixarene-based systems for electrochemical energy applications. Second, we summarize simulation studies on pillarquinone and calixquinone with intrinsic structures for applications in batteries. In addition, state-of-the-art applications of pillararene/calixarene-based systems in electrochemical energy storage devices such as lithium/sodium-ion batteries and supercapacitors are highlighted. The diverse roles they play and the various design strategies that have been investigated for high-performance pillararene/calixarene-based batteries are analyzed. Finally, we discuss the prospects for further developments in this emerging field. This review not only describes recent advances in pillararene/calixarene-based batteries and supercapacitors but also lays a firm groundwork for their further application in electrochemical energy engineering.

Nowadays, hydrogen technologies like fuel cells (FC) and electrolyzers, as well as rechargeable batteries (RBs) are receiving much attention at the top world economies, with public funding and private investments of multi-billion Euros over the next 10 years. Along with these technologies, electrochemical capacitors (ECs) are expanding rapidly in the energy storage market. Electrolyzers, RBs, FCs and ECs are electrochemical energy conversion and storage devices offering environmental and sustainable advantages over fossil fuel-based system. This overview discusses current trends in these electrochemical systems. It also examines recent advances on the CO2 reduction reaction, which has gained attention because of the capability of producing value-added chemical products at high efficiencies from the main greenhouse gas in the USA and the European Union. It is expected that these green systems will play a key role in the imminent implementation of a global sustainable energy scenario.

Supercapacitors possessing fast-charging characteristics and long lifespan are becoming increasingly important for powering portable and smart energy storage devices, and combining capacitive and battery-type materials into an integrated device is an effective method for increasing the overall performance of capacitors. Silicene is being designed as a cathode for the development of enhanced capacitance and ultra-cycle stable zinc-ion hybrid capacitors. Possessing a maximum areal capacity of 14 mF cm-2, a maximum power density of 9 mW cm-2, capacitance retention of 112% even after 10 000 cycles, and an unexpectedly high energy density of 23 mJ cm-2, this achievement of the zinc-ion hybrid capacitor would be superior to that of previously reported silicon-based supercapacitors. The DFT calculations further reveal that Zn ions dominate the capacitive behavior of the silicene electrode. The support association between silicene and zinc-ion hybrid capacitors so that they can take advantage of each other's strengths, which takes electrochemical energy technology to a stage, offering a straightforward proposal for integration and implementation of silicon-based materials.

The solution to the problem of negative impact on the ecology of fossil fuel consumption is the use of electrochemical energy sources. The special attractiveness has shown of lithium power sources is highlighted and the need to develop new cheap electrode materials and electrolytes with unique properties. The peculiarities of the behavior of lithium and the formation of a layer of reaction products on its surface upon contact with a liquid organic electrolyte have considered. The analysis of the main problems and ways of their solution at use of conversion electrodes of the II type for lithium-ion batteries has carried out. Emphasis is placed on the need to use in the development of new electrode materials of such parameters as capacity loading and accumulated irreversible capacity of the electrodes. The triad “electrode – solid electrolyte interphase – electrolyte” is considered as a basis of a systematic approach to the creation of new generations of lithium power sources. The optimal scenarios have proposed for the formation of an effective solid electrolyte interphase on the surface of the electrodes. The advantages of electrolytes based on fluoroethylene carbonate with synergistic acting additives of vinylene carbonate and ethylene sulfite are described. A new strategy for the use of “secondary” silicon nanomaterials to prevent direct contact of its surface with the electrolyte has considered. It has shown that the solid electrolyte interphase is a dynamic system that self-organizes from the unstable state into a stable one. The electrochemical behavior of electrodes with silicon nanocomposites with high capacity loading and low accumulated irreversible capacity has described.

Interfacial atomic configuration between dual-metal active species and nitrogen-carbon substrates is of great importance for improving the intrinsic activity of catalysts toward oxygen reduction reaction (ORR). Thus, from the atomic-scale engineering we develop a high intrinsic activity ORR catalyst in terms of incorporating atomically dispersed dual Fe centers (single Fe atoms and ultra-small Fe atomic clusters) into bamboo-like N-doped carbon nanotubes. Benefiting from atomically dispersed dual-Fe centers on the atomic interface of Fe-Nx/carbon nanotubes, the fabricated dual Fe centers catalyst exhibits an extremely high ORR activity (Eonset = 1.006 V; E1/2 = 0.90 V), beyond state-of-the-art Pt/C. Remarkably, this catalyst also shows a superior kinetic current density of 19.690 mA·cm−2, which is 7 times that of state-of-the-art Pt/C. Additionally, based on the excellent catalyst, the primary Zn-air battery reveals a high power density up to 137 mW·cm−2 and sufficient potential cycling stability (at least 25 h). Undoubtedly, given the unique structure-activity relationship of dual-Fe active species and metal-nitrogen-carbon substrates, the catalyst will show great prospects in highly efficient electrochemical energy conversion devices.

Metal sulfide arrays can store electrochemical energy owing to their high theoretical capacity, shortened diffusion routes, and rich electrochemical sites. However, their sluggish redox reaction has limited further application in high power density devices. Herein, a novel hybrid and hierarchical nanostructure with a thin layer of NiO deposited on the surface of walnut-like CoS particles is constructed and the NiO layer can greatly improve the capacitive properties of cobalt sulfide. In this hybrid nanostructure, the amount of NiO on the surface of CoS is precisely tuned to boost the electrochemical performance. Consequently, NiO/CoS exhibits a higher capacitance/capacity of 1749 F g−1/243.9 mAh g−1 fueled by the excellent electrical conductivity and appropriate surface structures. When assembled into a hybrid supercapacitor, the NiO/CoS//AC devices deliver a maximum capacitance of 60 C g−1 at 1.0 A g−1. Energy density reaches 45 Wh kg−1 when the power density is at 750 W kg−1. Additionally, the fabricated supercapacitor has good cycling stability with a capacity retention rate of 74% after 5000 cycles.

The electrochemical reduction of oxygen to water and the evolution of oxygen from water are two important electrode reactions extensively studied for the development of electrochemical energy conversion and storage technologies based on oxygen electrocatalysis. The development of an inexpensive, highly active, and durable nonprecious-metal-based oxygen electrocatalyst is indispensable for emerging energy technologies, including anion exchange membrane fuel cells, metal-air batteries (MABs), water electrolyzers, etc. The activity of an oxygen electrocatalyst largely decides the overall energy storage performance of these devices. Although the catalytic activities of Pt and Ru/Ir-based catalysts toward an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) are known, the high cost and lack of durability limit their extensive use for practical applications. This review article highlights the oxygen electrocatalytic activity of the emerging non-Pt and non-Ru/Ir oxygen electrocatalysts including transition-metal-based random alloys, intermetallics, metal-coordinated nitrogen-doped carbon (M-N-C), and transition metal phosphides, nitrides, etc., for the development of an air-breathing electrode for aqueous primary and secondary zinc-air batteries (ZABs). Rational surface and chemical engineering of these electrocatalysts is required to achieve the desired oxygen electrocatalytic activity. The surface engineering increases the number of active sites, whereas the chemical engineering enhances the intrinsic activity of the catalyst. The encapsulation or integration of the active catalyst with undoped or heteroatom-doped carbon nanostructures affords an enhanced durability to the active catalyst. In many cases, the synergistic effect between the heteroatom-doped carbon matrix and the active catalyst plays an important role in controlling the catalytic activity. The ORR activity of these catalysts is evaluated in terms of onset potential, number of electrons transferred, limiting current density, and durability. The bifunctional oxygen electrocatalytic activity and ZAB performance, on the other hand, are measured in terms of potential gap between the ORR and OER, ΔE = Ej10OER - E1/2ORR, specific capacity, peak power density, open circuit voltage, voltaic efficiency, and charge-discharge cycling stability. The nonprecious metal electrocatalyst-based ZABs are very promising and they deliver high power density, specific capacity, and round-trip efficiency. The active site for oxygen electrocatalysis and challenges associated with carbon support is briefly addressed. Despite the considerable progress made with the emerging electrocatalysts in recent years, several issues are yet to be addressed to achieve the commercial potential of rechargeable ZAB for practical applications.

Owing to their high energy density, lithium-oxygen batteries (LOBs) have been drawn great attention as one of the promising electrochemical energy sources. However, the sluggish kinetics of oxygen reduction/evolution reaction (ORR/OER) hamper the widespread application of LOBs. Herein, an elaborate designed catalysts which are constructed by FeNx moieties dispersed on the network-like hollow dodecahedral carbon and then decorated with Ru nanoparticles (FeNx-HDC@Ru). Since the homogeneously dispersed FeNx moieties could promote ORR performance, and the Ru nanoparticles could facilitate OER capability, the FeNx-HDC@Ru nanocomposites used as cathode catalysts can significantly improve LOBs performance. A lower discharge and charge overpotentials of 0.15 V and 0.78 V can be detected in the first cycle, respectively, and an excellent cycle performance of 90 cycles at 200 mA g−1 and 89 cycles at 500 mA g−1 can be demonstrated. Herein, the charge transfer kinetics has been enhanced with the internal network-like hollow structure and a low impedance Li2O2/catalysts contact interface could be earned by the constructed Ru nanoparticles, these factors would lead to an efficient acceleration to the formation and decomposition of Li2O2 during discharge and charge process.

Electrospinning has been proven as a highly versatile fabrication method for producing nano-structured fibres with controllable morphology, of both the fibres themselves and the void structure of the mats. Additionally, it is possible to use heteroatom doped polymers or to include catalytic precursors in the electrospinning solution to control the surface properties of the fibres. These factors make it an ideal method for the production of electrodes and flow media for a variety of electrochemical devices, enabling reduction in mass transport and activation overpotentials and therefore increasing efficiency. Moreover, the use of biomass as a polymer source has recently gained attention for the ability to embed sustainable principles in the materials of electrochemical devices, complementing their ability to allow an increase in the use of renewable electricity via their application. In this review, the historical and recent developments of electrospun materials for application in redox flow batteries, fuel cells, metal air batteries and supercapacitors are thoroughly reviewed, including an overview of the electrospinning process and a guide to best practice. Finally, we provide an outlook for the emerging use of this process in the field of electrochemical energy devices with the hope that the combination of tailored microstructure, surface functionality and computer modelling will herald a new era of bespoke functional materials that can significantly improve the performance of the devices in which they are used.

The economical, efficient and durable oxygen reduction catalysts facilitate the enhancement of electrochemical energy devices competitiveness towards widespread applications. In view of this, we provide an innovative sulfuration inducing method for the synthesis of ZnS and cobalt nanoparticles decorated N, S co-doped CNTs (ZnS/Co-NSCNTs) catalyst. S introduced into the zinc-based zeolitic imidazolate frameworks (ZIF-8) and cobalt-based zeolitic imidazolate frameworks (ZIF-67) precursors via pyrolysis, and induced the generation of ZnS/Co-NSCNTs have been confirmed by XRD, SEM, TEM, and XPS techniques. The key features including activity sites, transfer channels and adsorption energy back up the excellent electrocatalytic activity of the as-prepared ZnS/Co-NSCNTs towards oxygen reduction reactions (ORR). ZnS/Co-NSCNTs additionally exhibited a positive half-wave potential of 0.871 V (vs. RHE) with improved current density towards ORR. In alkaline medium, ZnS/Co-NSCNTs catalyst displayed a high tolerance towards methanol and an excellent long-term cycling stability. The observed onset potential for our prepared ZnS/Co-NSCNTs catalyst is analogous with the commercially available noble metal catalysts. Also, ZnS/Co-NSCNTs catalyst as a cathode in zinc-air battery displayed an enhanced electrochemical performance with a highly specific capacity of 750.1 mAh g−1, outstanding cycling stability, and high rate behavior. This work provides a new approach for the construction of stable low-cost alternative air-cathode catalysts for other energy conversion and storage applications.

Oxygen evolution and oxygen reduction are considered as essential processes in the energy conversion devices. The progress of cost-effective bifunctional catalysts has become a critical issue to be solved. Here, we report that Co(OH)2 @N-doped carbon (NC) was facilely synthesized through the impregnation strategy of metal-organic frameworks derived carbon and cobalt ions. N-doped carbon with porous structure and cobalt hydroxide nanosheets play a synergistic effect role, representing excellent catalytic performance toward oxygen evolution and reduction reactions. The obtained Co(OH)2@NC exhibits remarkable activity in terms of a lower overpotential of 330 mV@10 mA cm−2 for OER and a more positive half-wave potential (E1/2 = 0.84 V) for ORR in alkaline medium, outperforming IrO2 and Pt/C. Due to its superior bifunctional catalytic performance, Co(OH)2@NC catalyst is applied into a promising air electrode of Zn-air battery. This presented strategy of impregnation synthesis in this work provides a new design direction for practical electrochemical energy devices.

Electromagnetic pollution and electrochemical energy consumption have driven enormous endeavors in electromagnetic wave absorption materials and energy storage devices, however, designing versatile composites for addressing the issue remains a huge challenge. Herein, a versatile honeycomb-like N-doped carbon/bimetallic sulfide and oxide (N–CoFe2O4-CoxSy/FexSy@C) composites aerogel was designed via a simple mechanical mixing, freeze-drying and heat treatment method. As-prepared N–CoFe2O4-CoxSy/FexSy@C composites exhibited excellent electromagnetic wave absorption and electrochemical performances. The minimum RL can reach −51.9 dB at 15.5 GHz, with an effective frequency bandwidth (RL

The oxygen evolution reaction (OER) plays a paramount role in a variety of electrochemical energy conversion devices, and the exploration of highly active, stable, and low-cost electrocatalysts is one of the most important topics in this field. The exfoliated black phosphorus (EBP) nanosheet with a two-dimensional (2D) layered structure has high carrier mobility but is limited by excessive oxygen-containing intermediate absorption and fast deterioration in air. We here report the fabrication of nanohybrids of amorphous CoFeB nanosheets on EBP nanosheets (EBP/CoFeB). The 2D/2D heterostructure, thanks to the electronic interactions and oxygen affinity difference between EBP and CoFeB nanosheets, is capable of balancing the oxygen-containing intermediate absorption to an optimal status for facilitating the OER process. While the crystalline EBP contributes to the improved conductivity, the amorphous coating protects EBP and thus ensures the catalytic stability. The EBP/CoFeB electrocatalyst shows excellent OER performance with an ultralow overpotential of 227 mV at 10 mA cm-2 with an ultrasmall Tafel slope of 36.7 mV dec-1 with excellent stability. This study may inspire more researches to develop heterostructured nanohybrid electrocatalysts for a diversity of electrochemical reactions.

Reversible Solid Oxide Cells (r-SOCs) are an attractive electrochemical energy conversion technology that can act as both a Solid Oxide Fuel Cell (SOFC) for power generation, and a Solid Oxide Electrolysis Cell (SOEC) for steam electrolysis. Unfortunately, Ni-zirconia cermet, which is widely used in SOFCs, has the problem that the electronically conductive phases, Ni, agglomerates due to redox reactions and breaks the conductive path, resulting in performance degradation. In this study, we fabricated an alternative fuel electrode with a stable conductive structure using both an ionic conductor Ce0.9Gd0.1O2 (GDC) and an electronic conductor Sr0.9La0.1TiO3 (LST), and we co-impregnate Ni and GDC to the fuel electrode using only Ni as an electrocatalyst. The durability of the conventional fuel electrode and our alternative fuel electrode was compared and evaluated, and the potential of the alternative fuel electrode material was demonstrated.

The hybrid battery integrating a typical Zn redox battery and a Zn-air battery is a promising green technology for energy storage, and the cathode integrating the redox reaction and electrocatalytic oxygen reduction is a key point for efficient electrochemical energy conversion. Herein, we report a scalable strategy to fabricate nanoporous Ag2Al intermetallic compound as a self-standing cathode for the hybrid Zn battery. The abundant surface oxygen species, the Ag-Al intermetallic interaction and the np-Ag2Al@AgAlOx interface cooperatively contributed to the catalytic ORR activity. The electrode endows efficient catalytic oxygen reduction (a Tafel slope of 38.0 mV/dec and an onset potential of 0.998 V) and regulated redox activity as compared with Ag. The nanoporous channels allow efficient ion transport, interface charge exchange and gas molecular diffusion. Significantly, the assembled hybrid Zn-Ag2Al/air battery delivers a high capacity of 3.23 mAh/cm2 as compared with recent reports. As far as we know, this is the first exploration for the electrochemical property of Ag2Al, and it would inspire more exploration in developing multifunctional materials and robust hybrid batteries for practical applications.

The development of non-precious metal catalysts to replace scarce and costly Pt-based catalysts is crucial for oxygen reduction reaction (ORR), which involves various electrochemical energy conversions, such as fuel cells and metal-air batteries. However, it is still a challenge to devise a simpler method to obtain high-performance non-noble metal catalyst, which can be used for large-scale production. Herein, Cu and N co-doped mesocellular carbon foam (n-Cu/NC) has been developed by strong electrostatic adsorption (SEA) method, which inherits the original morphology of carbon foam, exhibiting high ORR performance with a half-wave potential of 0.825 V vs. RHE and excellent long-term durability. The outstanding performance of n-Cu/NC is attributed to the high specific surface area, hierarchical porous carbon matrix doped by multiple N atoms and uniform Cu2O/CuO active sites induced by the SEA method. The strategy of SEA method is applied to the preparation of carbon-supported catalysts, which shows great potential in the design and large-scale production of M and N co-doped carbon materials.

The oxygen reduction/evolution reactions (ORR/OER) are a key electrode process in the development of electrochemical energy conversion and storage devices, such as metal-air batteries and reversible fuel cells. The search for low-cost high-performance nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER alternatives to the widely-used noble metal-based catalysts is a research focus. This review aims to outline the opportunities and available options for these nanocarbon-based bifunctional electrocatalysts. Through discussion of some current scientific issues, we summarize the development and breakthroughs of these electrocatalysts. Then we provide our perspectives on these issues and suggestions for some areas in the further work. We hope that this review can improve the interest in nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER.

Characterization and electrochemical evaluation of novel metal-free electrocatalysts obtained by solar pyrolysis is reported. Carbon-based electrocatalysts were prepared from agave bagasse waste, using a sustainable process based on concentrated solar energy as heat source. Agave was processed in a spherical borosilicate glass solar reactor using a heating rate of 30 °C min−1 to a target of 500, 700, or 900 °C, and maintaining temperature for 1 h under inert atmosphere. The structure and composition of the prepared electrocatalysts were influenced by pyrolysis temperature. In addition, electrocatalytic activity towards the oxygen reduction reaction in 0.1 M KOH solution was explored. The electrocatalyst obtained at 500 °C showed the highest activity among all pyrolyzed samples due to its moderate surface area, but mostly due to its higher oxygen content. The metal-free electrocatalysts reported in this work are promising eco-friendly alternative as cathode materials for anion-exchange membrane fuel cells. This study provides a sustainable approach to use agricultural biomass waste to produce valuable materials for electrochemical energy devices.

Electrochemical energy technologies such as fuel cells, supercapacitors, and batteries are some of the most suitable energy storage and conversion devices to meet our needs proving the future generation’s equitable opportunity to meet their own needs. For this purpose, an earth-abundant precursor such as biomass is the best candidate for the synthesis of the next generation of low-cost and green electrode materials. This review summarizes the most recent progress in biomass-derived carbons for use in fuel cells, supercapacitors and lithium-ion batteries, the physical-chemical properties, desired features, performances, and limitations for electrochemical energy technologies. Several thermochemical treatments such as chemical activation, template methods, doping and hydrothermal treatments have been reviewed. Finally, we provide the reader with comprehensive information of the challenges, future research efforts, advantages, limitations and opportunities which will be a fundamental insight for the future design of biomass-derived carbon electrode materials for electrochemical storage and conversion systems.

The synthesis of nonprecious electrocatalysts for oxygen electrocatalysis is of considerable interest for the development of electrochemical energy devices. Herein, we demonstrate a facile approach for the synthesis of bamboo-like nitrogen-doped carbon nanotube-encapsulated Co0.25Ni0.75 alloy electrocatalyst (Co0.25Ni0.75@NCNT) and its bifunctional oxygen electrocatalytic performance toward oxygen reduction and oxygen evolution reactions. The Co0.25Ni0.75 alloy wrapped with NCNT is obtained by a one-step carbothermal reduction approach using dicyandiamide and NiCo-MOF precursors. Dicyandiamide acts as a nitrogen source, and the in situ generated Co0.25Ni0.75 alloy nanoparticles catalyze the growth of bamboo-like NCNTs. The hollow NiCo-MOF plays a sacrificial role in providing a suitable environment for the controlled growth of Co0.25Ni0.75 alloy and NCNT. Co0.25Ni0.75@NCNT efficiently catalyzes both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) at a favorable overpotential. It shows a low potential gap (ΔE) of ∼0.8 V between the two reactions, and it qualifies for the development of air cathode in metal-air batteries. The enhanced bifunctional activity and excellent durability stem from the chemical composition and the synergistic effect between Co0.25Ni0.75 alloy and encapsulating NCNT. The original phase and morphology of the catalyst is preserved after an extensive durability test. Aqueous rechargeable Zn-air battery (ZAB) is fabricated using a Co0.25Ni0.75@NCNT-based air cathode. The battery has high open-circuit voltage (1.53 V) and a maximum peak power density of 167 mW cm-2 with only 1.6% loss in the voltaic efficiency after 36 h charge-discharge cycles. As a proof-of-concept demonstration, the as-fabricated ZAB is successfully used for the electrochemical water splitting in alkaline solution.

Bipolar membranes (BPMs) are gaining interest in energy conversion technologies. These membranes are composed of cation- and anion-exchange layers, with an interfacial layer in between. This gives the freedom to operate in different conditions (pH, concentration, composition) at both sides. Such membranes are used in two operational modes, forward and reverse bias. BPMs have been implemented in various electrochemical applications, like water and CO2 electrolyzers, fuel cells, and flow batteries, while BPMs are historically designed for acid/base production. Therefore, current commercial BPMs are not optimized, as the conditions change per application. Although the ideal BPM has highly conductive layers, high water dissociation kinetics, long lifetime, and low ion crossover, each application has its own priorities to be competitive in its field. We describe the challenges and requirements for future BPMs, and identify existing developments that can be leveraged to develop BPMs toward the scale of practical applications.

Oxygen evolution reaction (OER), as the primary anodic reaction, plays a critical role in many electrochemical energy conversion processes. As the state-of-the-art OER catalysts, iridium-based materials are largely hindered from practical applications mainly due to the extreme scarcity of iridium. Here we demonstrate the successful fabrication of boron-doped amorphous iridium oxide (IrOx-B) via a facile boric acid-assisted method, which realizes an ultrahigh OER mass activity of 2779 A g Ir −1 at 300 mV overpotential, representing one of the best acidic OER catalysts reported so far. It is found that boric acid can not only facilitate the exposure of Ir, but also dope the amorphous IrOx with a form of metaborate, which could further modify the electronic and local ligand structure of Ir for the improved intrinsic activity. Interestingly, the reported strategy is universal that can be applied to improve other metal oxide OER catalysts, highlighting a versatile strategy for creating high-performance electro-catalysts with ultrahigh mass activity for OER and beyond.

Hierarchical 3-dimensional (3D) carbon nanostructures have potential applicability in several electrochemical energy applications own to their sizeable effective surface, specific energy density, cycling stability and flexibility. Herein, combining electrospinning with in situ chemical vapor deposition (CVD) technologies as an efficient and secure procedure is applied for constructing 3D carbon nanostructure-based on carbon fibers (CFs) and electrospun carbon nanofibers (ECNFs). Affect the catalysis type, immersion solution, carbon sources and treat temperature are experimentally demonstrated. Cactus-like 3D carbon nanomaterials are constructed via growth forest-like carbon nanofibers (CNFs) directly on both CNFs and CFs at 900 °C using Ni as a catalyst, cellulose acetate (CA) as carbon source and ethanol-urea as an immersions solution. The Ni/CNFs/ECNFs mat exhibits a large surface area of 342.3 m2 g−1, while just 19.3 m2 g−1 is recorded to Ni/CNFs/CFs. Based on the nano-nonwoven structure and forest-like grown CNFs nanostructure, Ni/CNFs/ECNFs exhibit a favorable hydrogen evolution reaction (HER) performance in an alkaline medium with a low overpotential of 88 mV to deliver 10 mV cm−2 current density and Tafel slope of 170 mV dec−1. This work proves the synthesis parameters of 3D hierarchical carbon nanostructures and their enticing to apply as an advanced substrate for electrochemical applications.

Engineering of nanostructured materials with a unique and uniform morphological design is considered to be a competent candidate for a diverse range of electrochemical energy applications. However, the construction of ball-in-ball transition metal sulfide via the vaporization process remains a big challenge of today's research community. In this work, carbon encapsulated nickel sulfide (Ni3S2@C) with a complex hollow interior was synthesized and further studied with nitrogen-doped carbon encapsulated nickel sulfide (Ni3S2@NC) for comparison basis. We used metal salt (nickel nitrate) and organic linker (trimesic acid, TMA) as a precursor to synthesize Ni-TMA via a solvothermal method. Next, the sulfidation process was done under 5% H2 balanced argon gas in a tubular furnace to convert into Ni3S2 with encapsulation of carbon. The prepared hybrid material showed ball-in-ball morphology and heazlewoodite mineral phase structure. Furthermore, the prepared materials were examined for electrochemical energy storage properties owing to their well-known faradaic dominant (battery-type) charge storage features and key positive electroactive material for today's growing hybrid electrochemical capacitor. The nitrogen-doped carbon encapsulated nickel sulfide has demonstrated good electrochemical features like a specific capacity of 442.45 F g−1 at 5 mV s−1 of scan rate and 373.52 F g−1 at 2 A g−1 of current density. Moreover, the material showed excellent capacitance retention of 81% and 70% after 5000 and 10,000 cycles run with 100% of coulombic efficiency at 8 A g−1.

Photoelectrochemical properties have been investigated for flexible photoelectrodes containing 310 nm thick ZnO film on spin-coated ITO/PET. The high crystalline structure of ZnO was studied using x-ray diffraction pattern. A value of 3.4 eV has been estimated for optical band gap from its absorption spectra. The flexible ZnO photoelectrode was demonstrated to generate photoelectrochemical current. The photocurrents are enhanced by 4% whereas flat-band potential is shifted by 8 V due to the illumination. Values of 1.022 and 0.714 AW−1 were found to be for photo switching and photoresponsivity, respectively. ZnO/ITO/PET can be used as a substrate for making flexible hybrid PEC devices to generate solar power and solar fuels.

Energy conversion and storage in a Li-ion cell involves multiple closely coupled transport processes, such as species diffusion through solid and solution phases in the electrode. Mathematical modeling of these processes is critical for fully understanding and optimizing the performance of a Li-ion cell. While a number of analytical and numerical models have been presented for solution phase diffusion, most of such work is based on the assumption of a constant current density. This paper presents analytical modeling of solution phase diffusion in a separate–electrode composite for a generalized, time-dependent current density. An analytical solution for the concentration field in a separator–electrode composite in such conditions is derived using the method of eigenfunction expansion. Good agreement with past work as well as numerical simulations is shown. Results for linear, periodic and step-function boundary conditions are discussed. The theoretical analysis presented here may help accurately model realistic processes where the applied current changes over time, for example, cyclic charge and discharge in an electric vehicle, or sudden changes in the battery load. Results presented here contribute towards the fundamental understanding of solution phase diffusion in Li-ion cells, and provide a basis for improving electrochemical energy conversion and storage processes.

Nitrogen-doped carbon dots (N-CDs), derived from the biomass (anthocyanin), are the novel additive to the nanocarbon materials, which is expected to bring a wide spectrum of novel applications. Moreover, metallic oxides are emerging for their unique potential for electrocatalysis. Herein, we report the synthesis of N-CDs for the selective detection of Fe3+ with a limit of detection of 2.57 μM in the range of 5–60 μM using ethylenediamine and H2O2 by a hydrothermal method. The obtained N-CDs displayed a spherical morphology with a particle size range of 2–7 nm and emitted blue luminescence at 394 nm under excitation at 319 nm. Meanwhile, we have demonstrated the fabrication of cost-efficient electrocatalysts for oxygen evolution reaction (OER) in an alkaline medium, employing N-CDs. Owing to the successful incorporation of N-CDs into NiO nanospheres, the resulting N-CDs/NiO with large surface areas, fast charge transfer, and increased conductivity vastly improved the catalytic activity. Remarkably, the optimal of N-CDs/NiO composite requires the overpotential of only 380 mV at a current density of 10 mA cm−2 and a relatively low Tafel slope of 57.96 mV dec−1 compared with pure NiO. These results open up a facile route for the application of N-CDs and offer prospects for CD-metal hybrids as high OER catalysts in electrochemical energy devices.

The conductive metal-organic frameworks (MOFs) are suggested as the ideal electrocatalysts for hydrogen evolution reaction (HER) because of the high utilization of metal atoms. Rational design and facile synthesis of MOFs with large specific surface area, proper metals as center, and tunable chemical components is still full of challenges. Herein, we report the facile synthesis three types of porous MOFs by regulating metal center using benzene-1,3,5-tricarboxylic acid (H3BTC) as organic ligand and have successfully synthesized the rhombic octahedral Cu-BTC, rod-shaped Co-BTC and spherical Ni-BTC materials with large specific surface area ranged in 350-500 m2 g−1. These as-prepared MOFs materials exhibit high performance of HER in 0.5 M H2SO4. Ni-BTC material exhibits the lowest overpotential of 53 mV at 10 mA cm-2 and the smallest Tafel slope of 62 mV dec−1 than those of Cu-BTC (270 mV, 155 mV dec−1) and Co-BTC (123 mV, 100 mV dec−1), which are much superior to these previously reported MOFs catalysts. In addition, the fast catalytic kinetic of Ni-BTC was confirmed by the smaller charge transfer resistance (Rct) value of 0.9 Ω and larger electrochemical active surface area (ECSA) of 35.5 cm2 than those of Cu-BTC (8.2 Ω, 22.5 cm2) and Co-BTC (1.9 Ω, 27.7 cm2). Because of the structural advantage and large ECSA, the turnover frequency (TOF) value of Ni-BTC reaches up to 0.041 s−1 at 120 mV overpotential, which is 20.5 and 2.6 times greater than that of Cu-BTC (0.002 s−1) and Co-BTC (0.016 s−1). Besides, these three types of MOFs exhibited excellent durability over 12 h. This study unfolds diverse insights into the design and facile synthesis of MOFs for electrochemical energy conversion system.

Biomass-derived activated carbon has attracted much attention in electrochemical energy systems, and its great potential can be further unlocked for achieving high-performance by tuning its composi...

Strain engineering is widely employed to manipulate the intrinsic relationship of activity and the crystal structure, while the mechanism and rational strategy toward high-performance devices are still under investigation. Here straining engineering is utilized to manipulate a series of a typical perovskite structures via introducing different types of heteroions (Bi1-xMxFeO3, M = Ca2+ or Y3+ ion). The space group R3c in BiFeO3 perovskites is found to be maintained with substituting a certain amount of heteroions at Bi3+ sites ( 5%). Such a transformation is linked with the mismatched crystal strain induced by the heteroions substituted at Bi3+ sites, while the activity, stability, and energy storage capability of Bi1-xMxFeO3 have been essentially varied. The results offer a strategy for manipulating stability and activity of perovskites in electrochemical energy conversion and storage.

Herein, synthesis of graphitic carbon nitride (g-C3N4) and its nanocomposites with monometallic nickel (Ni-g-C3N4), and bimetallic zirconium-nickel (ZrNi-g-C3N4) is reported. New materials for high storage performance are investigated eagerly in electrochemical energy applications. With this aim, the electrochemical method is used for the evaluation of hydrogen storage capacity (HSC) of the samples in the present research work. Synthesis of samples were carried out using a combination of thermal and hydrothermal methods. The evaluation of electrochemical hydrogen sorption and storage capability of g-C3N4 and its nanocomposites was done after sample characterization. Characterization techniques followed were powder X-ray diffraction (XRD), Nitrogen adsorption and desorption isotherms measurements at 77 K, thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometry (EDS). Cyclic voltammetric and chronopotentiometry measurements carried out in an alkaline medium helped to calculate the HSC. The discharge capacity was measured to be 82 mAhg−1 for g-C3N4, 182 mAhg−1 for Ni-g-C3N4 and 380 mAhg−1 for ZrNi-g-C3N4 at 1 mAg−1 of current density. Catalytic properties of the metal nanoparticles augment the storage capability of the g-C3N4 nanocomposites. These nanocomposites help to store hydrogen which serves as safe carrier in fuel cell applications.

The development of efficient and low-cost electrocatalysts toward the oxygen evolution reaction (OER) is critical for improving the efficiency of several electrochemical energy conversion and storage devices. Here, we report an elaborate design and synthesis of porous Co-based trimetallic spinel oxide nanoboxes (NiCo2-x Fex O4 NBs) by a novel metal-organic framework engaged strategy, which involves chemical etching, cation exchange, and subsequent thermal oxidation processes. Owing to the structural and compositional advantages, the optimized trimetallic NiCo2-x Fex O4 NBs (x is about 0.117) deliver superior electrocatalytic performance for OER with an overpotential of 274 mV at 10 mA cm-2 , a small Tafel slope of 42 mV dec-1 , and good stability in alkaline electrolyte, which is much better than that of Co-based bi/monometallic spinel oxides and even commercial RuO2 .