Electrochemical Energy Conversion Systems Research Articles

(Invited) Ceramic-Based Electrochemical Systems for Sustainable Transition to Zero-Carbon Energy

Realizing a sustainable energy future pose multiple challenges, especially with respect to our heavy dependence on fossil fuels. In that regard, electrochemical energy conversion systems based on ionically and mixed conducting ceramics offer unique opportunities for clean energy production from fossil fuels by abandoning the undesired air-based combustion that emits CO2 into the atmosphere and replacing it with oxygen-based electrochemical conversion processes, which produce capture-ready CO2 instead and avoid emissions. In the context of climate change, this distinction is critically important as processes that release CO2 unabatedly into the atmosphere must be avoided entirely. But that does not necessarily require that we should rush to abandon fossil fuels prematurely before we can replace them at-scale with clean energy alternatives.After framing the global energy landscape and threats to climate change, this presentation will discuss the opportunities and technical challenges of converting fossil fuels in solid oxide-base fuel cells with focus on solid fuels including coal. It will also introduce the new concept of electrochemical gasification to produce ‘blue’ hydrogen from fossil fuels without release of CO2 into the atmosphere. These technologies can help avoid major disruptions to energy supply and offer a smooth transition into a zero-carbon energy economy.

Modification of Fuel Electrode Microstructure for Protonic Ceramic Cells by the Infiltration of Various Metal Nanoparticles

Proton ceramic cells (PCCs) are promising eco-energy electrochemical energy conversion systems. Proton conducting perovskite oxide electrolytes of PCCs have high ion conductivity at intermediate and low temperatures because of their low activation energy. Most of electrode infiltration studies for fuel electrode supported PCCs were carried out on a thin air electrode layer rather than a thick fuel electrode. In the present study, various metallic nanoparticles (such as Ni, Pd and Pt) were infiltrated in fuel electrode scaffolds to increase the thriple phase boundary (TPB, electrode-electrolyte-gas phase). The fabricated fuel electrode supported PCC consisted of Ni-BaCe0.7Zr0.1Y0.1Yb0.1O3-ẟ cermet fuel electrode, BaCe0.7Zr0.1Y0.1Yb0.1O3-ẟ (BCZYYb) electrolyte, and BCZYYb-La0.6Sr0.4Co0.2Fe0.8O3-ẟ composite air electrode. SEM analysis results revealed that metallic nanoparticles can be infiltrated up to the fuel electrode functional layer and their distribution was uniform through the layer. The PCC with metal nanoparticle infiltrated fuel electrode exhibited higher power density and lower polarization resistance than that with bare fuel electrode. This study shows the electrochemical performance of fuel electrode supported PCCs can be further improved by the facile infiltration method.

Oxygen vacancies and tailored redox activity encountered with NiCo2O4 nanostructures for promising applications in supercapacitor and water oxidation

It is well known that transition metal oxides play a significant role in the development of efficient electrochemical energy storage and conversion systems. However, their application is limited by low electrical conductivity, a limited number of electroactive sites, and limited stability. In this study, nickel‑cobalt bimetallic oxide (NiCo2O4) nanostructures were prepared using orange peel extract and its fruit juice during hydrothermal method. The use of green chemical components from orange peel extract and its fruit juice was to demonstrate their ability to manipulate NiCo2O4's structural and functional properties. For this reason, the optimized 1 mL of orange peel extract and its fruit juice was found highly active for improving the electrochemical properties of NiCo2O4 nanostructures. The electrochemical supercapacitor performance of optimized NiCo2O4 nanostructures showed a specific capacitance of 997.50 Fg−1 with a cycling stability of more than thirty thousand cycles, resulting in a capacitance retention rate of almost 100 % at 1.5 Ag−1. In addition, during the oxygen evolution reaction (OER), the overpotential was 120 mV at 20 mA/cm2 and the Tafel slope was 110 mVdec−1, with a prolonged stability exceeding 45 h were observed for optimized NiCo2O4 nanostructures. With an electrode material comprising NiCo2O4 nanostructures and an orange peel extract, outstanding electrochemical performance was obtained. This could be explained by several factors, including high electroactive site exposure, rapid charge transfer kinetics, high hydroxide adsorption, oxygen vacancies on the surface, and abundance of Co(III). The approach described here can be used for the facile synthesis of a wide range of nanostructured functional materials that exhibit impressive electrochemical properties, particularly for energy storage and conversion applications.

Construction of Core-Shelled Covalent/Metal-Organic Frameworks for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) is the half-reaction in zinc-air batteries and water splitting. Developing highly efficient catalysts toward OER is a challenge due to the difficulty of removing four electrons from two water molecules. Covalent organic frameworks (COFs) provide the new chance to construct the highly active catalysts for OER, because they have controlled skeletons, porosities, and well-defined catalytic sites. In this work, core-shell hybrids of COF and metal-organic frameworks (MOFs) have first demonstrated to catalyze the OER. The synergetic effects between the COF-shell and MOF-core render the catalyst with higher activity than those from the COF and MOF. And the catalyst achieved an overpotential of 328mV, with a Tafel slope of 43.23mV dec-1 in 1m KOH. The theoretical calculation revealed that the high activity is from the Fe sites in the catalyst, which has suitable binding ability of reactant intermediate (OOH*), and thus contributed high activity. This work gives a new insight to designing COFs in electrochemical energy storage and conversion systems.

Metal-Organic-Framework-Based Nanoarrays for Oxygen Evolution Electrocatalysis.

The development of highly active and stable electrode materials for the oxygen evolution reaction (OER) is essential for the widespread application of electrochemical energy conversion systems. In recent years, various metal-organic frameworks (MOFs) with self-supporting array structures have been extensively studied because of their high porosity, abundant metal sites, and flexible and adjustable structures. This review provides an overview of the recent progress in the design, preparation, and applications of MOF-based nanoarrays for the OER, beginning with the introduction of the architectural advantages of the nanoarrays and the characteristics of MOFs. Subsequently, the design principles of robust and efficient MOF-based nanoarrays as OER electrodes are highlighted. Furthermore, detailed discussions focus on the composition, structure, and performance of pristine MOF nanoarrays (MOFNAs) and MOF-based composite nanoarrays. On the one hand, the effects of the two components of MOFs and several modification methods are discussed in detail for MOFNAs. On the other hand, the review emphasizes the use of MOF-based composite nanoarrays composed of MOFs and other nanomaterials, such as oxides, hydroxides, oxyhydroxides, chalcogenides, MOFs, and metal nanoparticles, to guide the rational design of efficient OER electrodes. Finally, perspectives on current challenges, opportunities, and future directions in this research field are provided.

Experimental and Theoretical Analysis of Immersion Cooling of a Li-Ion Battery Module

Abstract Overheating of Li-ion cells and battery packs is an ongoing technological challenge for electrochemical energy conversion and storage, including in electric vehicles. Immersion cooling is a promising thermal management technique to address these challenges. This work presents experimental and theoretical analysis of the thermal and electrochemical impact of immersion cooling of a small module of Li-ion cells. Significant reduction in both surface and core temperature due to immersion cooling is observed, consistent with theoretical and simulation models developed here. However, immersion cooling is also found to result in a small but non-negligible increase in capacity fade of the cells. A number of hypotheses are formed and systematically tested through a comparison of experimental measurements with theoretical modeling and simulations. Electrochemical Impedance Spectroscopy measurements indicate that the accelerated cell aging due to immersion cooling is likely to be due to enhanced lithium plating. Therefore, careful consideration of the impact of immersion cooling on long-term performance may be necessary. The results presented in this work quantify both thermal and electrochemical impacts of a promising thermal management technique for Li-ion cells. These results may be of relevance for design and optimization of electrochemical energy conversion and storage systems.

Breaking the Activity and Stability Bottlenecks of Electrocatalysts for Oxygen Evolution Reactions in Acids.

Oxygen evolution reaction (OER) is a cornerstone reaction for a variety of electrochemical energy conversion and storage systems such as water splitting, CO2 /N2 reduction, reversible fuel cells, and metal-air batteries. However, OER catalysis in acids suffers from extra sluggish kinetics due to the additional step of water dissociation along with its multiple electron transfer processes. Furthermore, OER catalysts often suffer from poor stability in harsh acidic electrolytes due to the severe dissolution/corrosion processes. The development of active and stable OER catalysts in acids is highly demanded. Here, we review the recent advances in OER electrocatalysis in acids and summarise the key strategies to overcome the bottlenecks of activity and stability for both noble-metal-based and noble metal-free catalysts, including i) morphology engineering, ii) composition engineering, and iii) defect engineering. Recent achievements in operando characterization and theoretical calculations are summarised which provide an unprecedented understanding of the OER mechanisms regarding active site identification, surface reconstruction, and degradation/dissolution pathways. Finally, we offer our views on the current challenges and opportunities to break the activity-stability relationships for acidic OER in mechanism understanding, catalyst design, as well as standardised stability and activity evaluation for industrial applications such as proton exchange membrane water electrolysers and beyond. This article is protected by copyright. All rights reserved.

Theoretical and experimental studies on the electrodeposited nanocrystalline Ag coatings from a novel Ag2O-based non-cyanide electrolyte

Functional silver coatings have been widely applied in fields of electrochemical energy conversion systems, electronics industry and antibacterial materials, and exploiting new non-cyanide silver electroplating bath system is of great significance for promoting the application. In this work, a new type of cyanide-free electrodeposited silver (Ag) system was developed with Ag2O as the main salt, 5,5-dimethyl hydantoin (DMH) as the silver ion complexing agent and potassium carbonate as the conductive salt. Comprehensive quantum chemical calculations demonstrate that the new silver-based system has the solvation structure of [Ag(C5H7N2O2)2]−(5N(2)-Ag). To further, roles of additives combination (L-cysteine and 2,2-bipyridine) and their fundamental mechanism on the silver electrodeposition process was further investigated by electrochemical tests and theoretical calculations. First-Principles calculation and simulation of molecular dynamics reveal that this additive couple have coordination interactions with Ag+, while strong adsorption on the Ag (111) surface. SEM and XRD analyses showed that the combination of L-cysteine and 2,2-bipyridine achieved an ideal silver coating with good morphology and a low grain size of 22.1 nm, verifying the great potential of the novel system to prepare high-quality silver coatings.

Progress in the Synthesis Process and Electrocatalytic Application of MXene Materials.

With their rich surface chemistry, high electrical conductivity, variable bandgap, and thermal stability, 2D materials have been developed for effective electrochemical energy conversion systems over the past decade. Due to the diversity brought about by the use of transition metals and C/N pairings, the 2D material MXene has found excellent applications in many fields. Among the various applications, many breakthroughs have been made in electrocatalytic applications. Nevertheless, related studies on topics such as the factors affecting the material properties and safer and greener preparation methods have not been reported in detail. Therefore, in this paper, we review the relevant preparation methods of MXene and the safer, more environmentally friendly preparation techniques in detail, and summarize the progress of research on MXene-based materials as highly efficient electrocatalysts in the electrocatalytic field of hydrogen precipitation reaction, nitrogen reduction reaction, oxygen precipitation reaction, oxygen reduction reaction, and carbon dioxide reduction reaction. We also discuss the technology related to MXene materials for hydrogen storage. The main challenges and opportunities for MXene-based materials, which constitute a platform for next-generation electrocatalysis in basic research and practical applications, are highlighted. This paper aims to promote the further development of MXenes and related materials for electrocatalytic applications.

Advances and Regulation Strategies of the Active Moiety in Dual‐Atom Site Catalysts for Efficient Electrocatalysis

AbstractDual‐atom site catalysts (DACs) have emerged as a new frontier in the heterogeneous catalysis field for electrochemical energy conversion systems. In this review, the superiority of DACs over single‐atom site catalysts is fully discussed. The origin of synergistic effects such as optimized d‐band structure, tailored spin state, and tuned charge transfer are pointed out. The merits in geometric and electronic structure render the active moiety versatile binding behavior toward adsorbed intermediate and beneficial synergistic effects to break the scaling relationships. The approaches to engineer the active moiety of DACs through modulating the central atoms, tuning the coordination environment, and engineering the metal‐support interaction are summarized. Finally, the current challenges and future research perspectives of DACs for efficient electrocatalysis are outlined.

Structure and Reactivity of Metal-Oxide-Supported Noble Metal Nanoparticles: Electrooxidation of Simple Organic Molecules

There has been growing interest in utilizing small (simple) organic molecules, as alternative fuels to hydrogen, in electrochemical energy conversion systems. In addition to ethanol (biofuel), that can be ideally oxidized to carbon dioxide thus delivering twelve electrons, recent important systems include dimethyl ether as well. But realistically the respective reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials.Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium.We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol, ethanol, formic acid and dimethyl ether. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

(Invited) Multiscale Diffusion-Reaction Heat Transfer Analysis for Predicting Thermal Runaway in Li-Ion Cells and Battery Packs

Thermal runaway in Li-ion cells and battery packs remains a topic of much importance for ensuring the safety of electrochemical energy conversion and storage systems. Thermal runaway also indirectly affects performance, as conservative overdesign to reduce the risk of thermal runaway affects system-level performance metrics such as energy storage density. Given the considerable challenges in experimental investigation of thermal runaway, theoretical models to predict thermal runaway characteristics of a cell or battery pack are critically needed. Such models can help guide the design of experiments, and ensure that practical systems are reasonably safe without being needlessly overdesigned.This talk will summarize ongoing work on theoretical analysis of multilayer diffusion-reaction heat transfer problems for predicting thermal runaway in Li-ion cells and battery packs. Following a linearization of heat generation terms, the governing energy conservation equation is solved in a multilayer geometry representative of a Li-ion cell comprising multiple electrode and separator layers, or of a battery pack containing several cells. It is mathematically shown that under certain conditions, this problem may admit a finite number of imaginary eigenvalues, which are shown to cause thermal runaway. It is shown that the occurrence of imaginary eigenvalues is governed by a delicate balance between heat generation, thermal conduction within the multilayer body and heat removal from the boundaries, based on which, an explicit threshold condition for thermal runaway is derived. This threshold condition is interpreted in the context of parameter values relevant to Li-ion cells. For example, it is shown that boundary cooling is severely limited in its role to prevent thermal runaway, whereas improving thermal transport within the cell is likely to be a lot more effective. This theoretical model is also extended to a two-layer problem comprising a finite layer adjoined by a semi-infinite body that may model immersion cooling of a Li-ion cell or battery pack. It is shown that while this diffusion-reaction problem is, in principle, unconditionally unstable, the finite time period of any discharge process may allow the temperature field to still remain within a safe envelope, if designed appropriately. Based on this mathematical model, scenarios related to immersion cooling of pouch cells are investigated.The theoretical work described in this talk is broadly relevant to several diffusion-reaction systems. In the particular context of Li-ion cells, these results may form the foundation of techniques to proactively predict and prevent thermal runaway in Li-ion cells and battery packs.

Surface-Engineered Zn-Based Alloys Anodes for Aqueous Zn Batteries

Safety and durability concerns caused by surface and interface instabilities of high-surface-activity energy materials are challenging modern electrochemical energy conversion and storage systems. In this presentation, I will present our most recent representative works on the surface engineering of functional materials for aqueous batteries. In this work, we designed an in-situ visualized protocol that can exactly mimic the actual electrochemical environments used in aqueous batteries. Using this novel protocol, we observed the dynamic processes of metal plating/stripping on the alloys in aqueous batteries. Comprehensive and systematic studies based on experimental, theoretical, spectroscopic, and microscopic approaches prove that absolute reversibility can be achieved by using the proposed 3D alloys because of the significantly improved Zn diffusion and successfully suppressed dendrite growth. As a proof-of-concept, the novel alloy structures deliver unprecedented stability with nearly 100% Coulombic efficiency over thousands of cycles even under harsh electrochemical conditions, including testing in seawater-based aqueous electrolytes and using a high current density of 80 mA cm-2.

(Invited) 2D Nitride Mxenes with Unusual Chemistries for Carbon-Neutral Energy

The large-scale shift towards renewable energy technology requires the ability to reliably convert and store electrochemical energy. This technology is still limited in terms of performance, cost, and/or ease of utilization. In recent years, two-dimensional (2D) materials have been explored as low-cost, high-performing catalysts and electrodes for the reliable conversion and storage of electrochemical energy. Of these 2D materials, a special class of carbides and nitrides, known as MXenes, have gained popularity due to their high tunability, conductivity, and high surface area-to-volume ratio. From these carbide and nitride MXenes, the nitrides have received less attention due to a lack of reliable synthesis methods, despite being theorized to outperform their carbide counterparts. In this presentation, I will present on the oxygen-assisted molten salt fluoride synthesis method developed in my group to produce phase-pure nitride MXenes. Along with this, I will provide evidence of the enhanced capabilities of the nitride family of MXenes compared to carbides, sulfides, and oxides, when applied in the nitrogen reduction reaction (NRR), hydrogen evolution reaction (HER), and supercapacitor applications. In each of these fields, the enhanced performance is investigated using in-situ/operando spectroelectrochemical techniques. I will wrap up by discussing the future directions in the field of MXenes that require further attention for the full exploitation of their properties in electrochemical energy storage and conversion systems to attain carbon-neutral energy.

Transient Solid Oxide Cell Reactor Model Used in rSOC Mode-Switching Analysis and Power Split Control of an SOFC-Battery Hybrid

Defossilization of the global energy system requires a transition towards intermittent renewable energy sources and approaches that enable efficient conversion of primary energy sources into electrical energy. Due to their high efficiency in converting chemical into electrical energy and vice versa, solid oxide cell (SOC) systems provide solutions for both of these aspects. Within this contribution, two researched cases utilizing SOC's are presented, based on simulation studies and experiments.Characteristically, SOC reactors produce hydrogen from steam in solid oxide electrolysis (SOE) mode, or electricity from reformates in solid oxide fuel cell (SOFC) mode. An application of both modes as reversible solid oxide cell (rSOC) is to balance a renewable power supply with storage and power production, leading to high utilization of the same equipment. An application in SOFC mode is the maritime transportation powertrain. In both cases, transient operation is needed whenever mode transitions occur. In particular, switching between rSOC modes implies transitioning exothermal SOFC, endothermal, thermoneutral and exothermal SOE operation. Similarly, supplying the power demand of a maritime drivetrain in SOFC mode leads to various exothermic levels, as pertinent to part or full load operation. Operating strategies are needed to suppress potentially damaging thermal stresses during these transitions in the electrochemical SOC reactors. In order to identify such operating strategies, experiments have been carried out and a transient model has been developed for the analysis of rSOC mode-switching and SOFC drivetrain power supply, which are presented in this study. The 1D+1D SOC dynamic multi-reactor model includes the individual SOC reactors, piping and insulation, and is implemented in the in-house developed transient energy process system simulation framework TEMPEST [1,2]. The model couples the transient balances of mass and energy with electrochemistry, internal reforming kinetics, heat transfer, and flow distribution. As a result, temperature and voltage characteristics at cell, stack, and module levels are obtained to analyze for e.g. unwanted thermal stress. In the EU project SWITCH [3], experiments were performed at DLR with a Large Stack Module (LSM) from SolydEra (formerly SOLIDpower) to validate the model in transient 75 kW electrolysis mode, 25 kW fuel cell mode and mode-switching operation between electrolysis and polygeneration mode. The so called polygeneration mode refers to simultaneous generation of hydrogen and electricity at partial fuel utilization with natural gas, biogas or e-methane. Simulative studies of mode-switching procedures from SOE to SOFC-mode polygeneration show that drawing fuel cell current soon after reaching open circuit voltage and sufficiently in advance of the methane ramp completion leads to a reduced temperature decrease at the inlet of the cell without reaching oxygen to carbon ratios low enough to favor carbon deposition. In the EU project NAUTILUS [4], the mismatch between the transient response possibilities of SOFC systems and the power demand of a ship is addressed by connecting Li-ion batteries to the powertrain. Batteries respond to highly transient ship load demand changes, while the SOFC’s provide base part load to full load, according to a power split control strategy. A battery model developed and parametrized by the Chair for Electrochemical Energy Conversion and Storage Systems of RWTH Aachen University [5] was added to TEMPEST and validated using DLR experiments with a 40 kWh Li-ion battery. Simulation results of the SOFC-battery hybrid in Figure 1 show that a rule-based power split control strategy [6] ensures that the power demand of the ship is met at all times while the battery state of charge (SoC) remains within specified range, and the SOFC power is drawn at one of three fixed power levels for reduced thermal stress. An experimental campaign to test this and other control strategies with a 32 kW LSM from SolydEra and the 40 kWh battery is in progress at DLR. Acknowledgements Project SWITCH has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No 875148. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research. Project NAUTILUS has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 861647.

Ultrafine Pt NanoparticlesAnchored on 2D Metal-Organic Frameworks as Multifunctional Electrocatalysts for Water Electrolysis and Zinc-Air Batteries.

Multifunctional electrocatalysts are crucial to cost-effective electrochemical energy conversion and storage systems requiring mutual enhancement of disparate reactions. Embedding noble metal nanoparticles in 2D metal-organic frameworks (MOFs) are proposed as an effective strategy, however, the hybrids usually suffer from poor electrochemical performance and electrical conductivity in operating conditions. Herein, ultrafine Pt nanoparticles strongly anchored on thiophenedicarboxylate acid based 2D Fe-MOF nanobelt arrays (Pt@Fe-MOF) are fabricated, allowing sufficient exposure of active sites with superior trifunctional electrocatalytic activity for hydrogen evolution, oxygen evolution, and oxygen reduction reactions. The interfacial Fe─O─Pt bonds can induce the charge redistribution of metal centers, leading to the optimization of adsorption energy for reaction intermediates, while the dispersibility of ultrafine Pt nanoparticles contributes to the high mass activity. When Pt@Fe-MOF is used as bifunctional catalysts for water-splitting, a low voltage of 1.65V is required at 100mA cm-2 with long-term stability for 20h at temperatures (65°C) relevant for industrial applications, outperforming commercial benchmarks. Furthermore, liquid Zn-air batteries with Pt@Fe-MOF in cathodes deliver high open-circuit voltages (1.397V) and decent cycling stability, which motivates the fabrication of flexible quasisolid-state rechargeable Zn-air batteries with remarkable performance.

Coordination Engineering of Dual Co, Ni Active Sites in N-Doped Carbon Fostering Reversible Oxygen Electrocatalysis.

The development of affordable and non-noble-metal-based reversible oxygen electrocatalysts is required for renewable energy conversion and storage systems like metal-air batteries (MABs). However, the nonbifunctionality of most of the catalysts impedes their use in rechargeable MAB applications. Moreover, the loss of active sites also affects the long-term performance of the electrocatalyst toward oxygen electrocatalysis. In this work, we report a simplistic yet controllable chemical approach for the synthesis of dual transitional metals such as cobalt, nickel, and nitrogen-doped carbon (CoNi-NC) as bifunctional electrode materials for rechargeable zinc-air batteries (ZABs). The spatially isolated Ni-N4 and Co-N4 active units were rendered for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. The individual efficacy of both reversible reactions enables an ΔE value of ∼0.72 V, which outperforms several bifunctional electrocatalysts reported in the literature. The half-wave potential (E1/2) and overpotential were achieved at 0.83 V and 330 mV (vs RHE) for ORR and OER, respectively. The peak power density of ZAB equipped with the CoNi-NC catalyst was calculated to be 194 mW cm-2. The present strategy for the synthesis of bifunctional electrocatalysts with dual active sites offers prospects for developing electrochemical energy storage and conversion systems.

Optimized oxygen deficient mesoporous barium doped cobalt oxide: A wonder material for green energy generation and storage

Electrochemical energy conversion and storage systems are presently playing a lead role in the global energy platform. This study reports the fabrication of a Hydroelectric Cell (HEC) via the synthesis of oxygen-deficient barium-doped Co3O4 multifunctional material using a solid-state method for green electrical energy generation and storage applications. Different analytical methods were used to characterize the material. The Transmission and Scanning Electron micrographs of pure Co3O4 and Ba- Co3O4 revealed that doping with Barium metal into Co3O4 causes a change in morphology from a spherical shape to a sheet-like structure. The UV–vis spectroscopy indicates that the doping enhanced the band gap of Co3O4 from 1.65 to 2.52 eV and Brunauer Emmett Teller's investigation shows an increase in specific surface area from 8 m2/g to 13 m2/g. Further, an increase in oxygen deficiency due to Ba doping was confirmed with Photoluminescence spectroscopy, Electron Paramagnetic Resonance, and X-ray photoelectron spectroscope. The short circuit current of barium-doped HEC increased by 13 folds as compared to the undoped cell from 1.7 mA/cm2 to 21.6 mA/cm2, and its peak power increased by 18 times from 12.5 W/m2 to 227 W/m2. The power obtained from Ba-doped HEC is higher than typical solar panels of the same area and HEC has an edge over solar cells that it needs no light to produce energy therefore it can be used in the dark also. The specific capacitance of pure Co3O4 was 282.01 F/g which increased to 451.83 F/g after Ba doping. Moreover, the charge–discharge stability studies have established that the Ba- Co3O4 has a remarkable specific capacitance retention capability of 95% even after 2000 continuous charge-discharge cycles. Since this process involves water splitting, therefore hydrogen gas is produced as a byproduct that can be used for further energy generation. Thus, this material has enormous potential for application in the field of electrical energy generation, storage, and hydrogen gas production.

Nickel as a key element in the future energy

The review discusses the complex properties of nickel and its role as a critical element for ensuring a confident transition to a new technological paradigm from fossil fuels in favor of using advanced electrochemical storage and energy conversion systems. The main classes of nickel-containing materials of the positive electrode (cathode) for metal-ion batteries are discussed, the place of nickel among other 3<i>d</i>-metals used in the industry of electrochemical energy storage is determined. The main methods and approaches for the synthesis of state-of-the-art and next generation cathode materials based on layered Ni-containing oxides are presented. The crystal and electronic structures of these materials, including their evolution in the process of (de)intercalation of alkali metal cations, are considered in the context of their electrochemical properties. The most acute problems facing modern materials science on the way to commercialization and industrial production of new generation highenergy density cathode materials are determined. At the end of the review, promising directions for the further development of nickelcontaining cathode materials are outlined.<br> The bibliography includes 252 references.

Bimetallic MoO3/Ni-N-C Nanoalloys Derived from MOFs for Electrocatalytic Urea Oxidation Reaction

In electrochemical energy storage and conversion systems, urea oxidation reaction (UOR) can produce hydrogen and mitigate pollution from urea-rich wastewater in a low-energy manner, whereas the development of this technique was limited via a lack of economical and cost-effective UOR catalysts. Herein, a unique electrocatalyst of MoO3/Ni-N-C was synthesized from a Mo element-incorporated Ni-MOF by heating under an inert atmosphere. The prepared MoO3/Ni-N-C electrode shows superior activity toward UOR, which only needs a low potential of 1.42 V (vs RHE) at 50 mA cm–2 in 1.0 M KOH with 0.5 M urea. The excellent performance for UOR is attributed to the synergistic effect between molybdenum and nickel, the modulation of the electronic structure for the nickel site by MoO3, accelerating the charge transfer, and tuning the reaction interface adsorption energy to enhance electrocatalytic activity. This work provides strategies and directions for exploring other advanced UOR electrode material designs.