Oxygen Reduction Reaction/oxygen Evolution Reaction Research Articles

Exploring the synergistic effect of palladium nanoparticles and highly dispersed transition metals on carbon nitride/super-activated carbon composites for boosting electrocatalytic activity

In the present work, multifunctional electrocatalysts formed by palladium nanoparticles (Pd NPs) loaded on Fe or Cu-containing composite supports, based on carbon nitride (C3N4) and super-activated carbon with a high porosity development (SBET 3180 m2/g, VDR 1.57 cm3/g, and VT 1.65 cm3/g), were synthesised. The presence of Fe or Cu sites favoured the formation of Pd NPs with small average particle size and a very narrow size distribution, which agreed with Density Functional Theory (DFT) calculations showing that the interaction of Pd clusters with C3N4 flakes is weaker than with Cu- or Fe-C3N4 sites. The electroactivity was also dependent on the composition and, as suggested by preliminary DFT calculations, the Pd-Cu catalyst showed lower overpotential for hydrogen evolution reaction (HER) while bifunctional oxygen reduction reaction/ oxygen evolution reaction (ORR/OER) behaviour was superior in Pd-Fe sample. The Pd-Fe electrocatalyst was studied in a zinc-air battery (ZAB) for 10 h, showing a performance similar to a commercial Pt/C + RuO2 catalyst with a high content of precious metal. This study demonstrates the synergistic effect between Pd species and transition metals and shows that transition metals anchored on C3N4-based composite materials promote the electroactivity of Pd NPs in HER, ORR and OER due to the interaction between both species.

Increasing the bifunctional OER/ORR activity of 3d transition metals doped g-C3N3 by controlling the charge states

Pursuing efficient bifunctional oxygen reduction reaction/ oxygen evolution reaction (OER/ORR) electrocatalysts is crucial for realizing sustainable and renewable clean energy, yet it remains a formidable challenge. In this study, we employ density functional theory and machine learning (ML) predictions to systematically investigate the bifunctional OER/ORR activity of 3d transition metal (TM) atom-doped g-C3N3. Our findings reveal that N-rich and C-poor growth conditions can facilitate 3d TM doping into g-C3N3. The Ni occupation N in 0 (Ni×N@C54N53, including 54 C and 53 N atoms), Ni occupation N in +1 (Ni•N@C54N53) and Ni interstitial sites in +1 charge state (Ni•int@C54N54, including 54 C and 54 N atoms) meet the requirements of bifunctional OER/ORR electrocatalysts, which because they (1) have lower formation energies, and (2) lower overpotentials (smaller than 0.47V), (3) can maintain stability under 300K and (4) their band gaps are decreased, which leads to facilitating electron transfer. ML predictions identify the 3d band center (εd) and the number of 3d electrons (Ne) as the most effective descriptors for overpotentials of OER and ORR, respectively. This work can pave the way for understanding the origin of bifunctional OER/ORR activity of 3d-TM doped g-C3N3 and benefit the rational design of novel electrocatalysts for other catalytic reactions by considering the charge states.

The chemical state of iron species influence on the performance of Fe–N–C bifunctional electrocatalyst for Zn–air batteries

Fe–N–C materials have emerged as promising alternatives to precious metals for oxygen reduction reaction/oxygen evolution reaction (ORR/OER). In this study, a strategy is presented to investigate the influence of different chemical states of iron species in Fe–N–C materials on their electrocatalytic performance. Three Fe–N–C catalysts, containing either zero-valent Fe or Fe3O4 nanoparticles, are synthesized using acid pickling, high-speed centrifugation and ultrasound-assisted hydrothermal methods, respectively. The findings manifest that the chemical state of iron significantly affects the electrocatalytic activity of Fe–NX active sites, namely zero-valent Fe enhancing Fe–NX activity while Fe3O4 weakening its activity. Notably, the Fe@FeNC catalyst containing only zero-valent iron, demonstrates the only 0.621 V potential difference between the ORR half-wave potential and the OER potential at 10 mA cm−2. Furthermore, the rechargeable Zn–air battery assembled with Fe@FeNC as the air cathode exhibits a remarkable peak power density of 179.0 mW cm−2, excellent cycling stability over 210 h (with a cycle frequency of one every 10 min), and the minimal voltage gap of 0.710 V. These results reveal the significance of different chemical states of metal-based nanoparticles in Fe–NX activity of Fe–N–C catalysts and offer insights into the rational design of electrocatalysts with exceptional activity and versatile applications.

Research Progress of Perovskite-Based Bifunctional Oxygen Electrocatalyst in Alkaline Conditions.

In light of the depletion of conventional energy sources, it is imperative to conduct research and development on sustainable alternative energy sources. Currently, electrochemical energy storage and conversion technologies such as fuel cells and metal-air batteries rely heavily on precious metal catalysts like Pt/C and IrO2, which hinders their sustainable commercial development. Therefore, researchers have devoted significant attention to non-precious metal-based catalysts that exhibit high efficiency, low cost, and environmental friendliness. Among them, perovskite oxides possess low-cost and abundant reserves, as well as flexible oxidation valence states and a multi-defect surface. Due to their advantageous structural characteristics and easily adjustable physicochemical properties, extensive research has been conducted on perovskite-based oxides. However, these materials also exhibit drawbacks such as poor intrinsic activity, limited specific surface area, and relatively low apparent catalytic activity compared to precious metal catalysts. To address these limitations, current research is focused on enhancing the physicochemical properties of perovskite-based oxides. The catalytic activity and stability of perovskite-based oxides in Oxygen Reduction Reaction/Oxygen Evolution Reaction (ORR/OER) can be enhanced using crystallographic structure tuning, cationic regulation, anionic regulation, and nano-processing. Furthermore, extensive research has been conducted on the composite processing of perovskite oxides with other materials, which has demonstrated enhanced catalytic performance. Based on these different ORR/OER modification strategies, the future challenges of perovskite-based bifunctional oxygen electrocatalysts are discussed alongside their development prospects.

A unique nanocomposite with FeCo nanoalloy anchored on S, N co-doped carbonaceous matrix for high bifunctional oxygen reduction reaction/oxygen evolution reaction electrocatalytic property in Zn-air battery.

A unique nanocomposite of FeCo-NSCC (means FeCo nanoalloy anchored on N, S co-doped carbonaceous composite) is obtained by one-pot pyrolysis using mixed natural wool fibers, dicyandiamide and the corresponding metal salts. The FeCo-NSCC has a higher degree of graphitization and a high specific surface area of 359m2 g-1. The FeCo-NSCC exhibits a promising bifunctional oxygen reduction reaction/oxygen evolution reaction (OER/ORR) electrocatalytic activity with onset potential and half-wave potentials of 0.980 and 0.853V vs reversible hydrogen electrode for ORR, and a low overpotential of 351mV at 10mAcm-2 for OER, superior to that of state-of-the-art commercial Pt/C and RuO2. The FeCo-NSCC presents a vigorous bifunctional OER/ORR electrocatalytic activities with the low ΔE(E1/2 - Ej=10) of 0.727V, superior to most of the reported non-noble metal-based catalysts. Besides, the FeCo-NSCC shows remarkable durability and methanol resistance. The FeCo-NSCC based battery works at an open circuit voltage of 1.52V and has a maximum power density of 161 mW cm-2 at current density of 246mAcm-2, better than those of Pt/C-RuO2 based battery (1.47V; 106 mW cm-2, 145mAcm-2). The FeCo-NSCC based battery is stable with no obvious increased voltage gap after 60h cycles.

RuO2-Incorporated Co3O4 Nanoneedles Grown on Carbon Cloth as Binder-Free Integrated Cathodes for Tuning Favorable Li2O2 Formation.

Developing ideal Li-O2 batteries (LOBs) requires the discharge product to have a large quantity, have large contact area with the cathode, and not passivate the porous surface after discharge, which put forward high requirement for the design of cathodes. Herein, combining the rational structural design and high activity catalyst selection, minor amounts of RuO2-incorporated Co3O4 nanoneedles grown on carbon cloth are successfully synthesized as binder-free integrated cathodes for LOBs. With this unique design, plenty of electron-ion-oxygen tri-phase reaction interface is created, the side reaction from carbon is isolated, and oxygen reduction reaction/oxygen evolution reaction (OER) kinetics are significantly facilitated. Upon discharge, film-like Li2O2 is observed growing on the needle surface first and eventually ball-like Li2O2 particles form at each tip of the needle. The cathode surface remains porous after discharge, which is beneficial to the OER and is rare in the previous reports. The battery exhibits a high specific discharge capacity (7.64 mAh cm-2) and a long lifespan (500 h at 0.1 mA cm-2). Even with a high current of 0.3 mA cm-2, the battery achieves a cycling life of 200 h. In addition, punch-type LOBs are fabricated and successfully operated, suggesting that the cathode material can be utilized in ultralight, flexible electronic devices.

Enhancing the Reaction Kinetics and Reversibility of Li–O2 Batteries by Multifunctional Polymer Additive

AbstractAs a potential candidate for next‐generation energy storage systems, Li–O2 batteries (LOBs) with their attractive theoretical energy density have triggered great interest. However, tough issues of sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics, poor rechargeability, superoxide‐derived side reactions, and Li‐metal corrosion in LOBs limit their practical applications. Herein, a poly(2,2,2‐trifluoroethyl methacrylate) (PTFEMA) additive is introduced into the typical electrolyte, giving superior cycling performance to LOBs. Enabling strong solvation of Li+, PTFEMA regulates a uniform Li+ flow at the cathode and anode sides of LOBs. Induced by homogeneous Li+ flux and favorable adsorption with superoxide species, PTFEMA promotes superoxide transformation in the ORR and inhibits superoxide‐induced parasitic reactions. Uniform Li+ flux gives evenly‐distributed Li2O2 that can be completely decomposed during OER. In addition, PTFEMA protects Li‐metal against corrosion from O2, superoxide, and byproducts shuttle. Hence, accelerated ORR/OER kinetics, facilitated rechargeability, suppressed superoxide‐derived side reactions, and well‐protected Li‐metal can be simultaneously realized with PTFEMA, resulting in significantly enhanced electrochemical performance of LOBs. This electrolyte engineering involving facile multifunctional polymer additives provides a practical alternative to complex componential optimization toward commercial LOBs and gives insight to the understanding of uniform Li+ flux on reaction kinetics and reversibility.

Pyrochlores for Advanced Oxygen Electrocatalysis.

Fuel cells (FCs), water electrolyzers (WEs), unitized regenerative fuel cells (URFCs), and metal-air batteries (MABs) are among the emerging electrochemical technologies for energy storage, fuel (H2), oxidant (O2), and clean energy production. Their commercial applications are hindered by the low oxygen reduction reaction/oxygen evolution reaction (ORR/OER) bifunctional activity (for URFCs and MABs), OER selectivity (brine electrolysis in seawater and Martian environments), and high cost of the benchmark electrocatalysts (OER: RuO2, IrO2 and ORR: Pt/C) which affects the performance and affordability of the devices. Low-cost electrocatalysts with highly symmetric ORR/OER bifunctional activity and high OER selectivity are crucial for large-scale FC, WE, URFC, and MAB application. Recent studies have revealed that tuning the structure of pyrochlore oxides provides a pathway to enhancing OER and ORR activity over a wide range of pH. Pyrochlore oxides commonly contain a cubic A2B2O7-x structure with two types of tetrahedrally coordinated O atoms containing (1) A-O-A and (2) A-O-B types with a cationic radii mismatch of rA/rB > 1.5 and propensity toward oxygen vacancy formation. The variety of pyrochlore oxides and their tunable properties make them attractive for a wide spectrum of applications. Among all the metal oxides, Ru-based pyrochlores (e.g., Pb2Ru2O7-x) exhibit the best bifunctional oxygen electrocatalytic activity, i.e., low bifunctionality index (BI), in alkaline medium. Furthermore, pyrochlores exhibit high OER selectivity in brine electrolytes due to the presence of surface oxygen vacancies, making them suitable for space applications (brine electrolysis on Mars) and coastal hydrogen generation. Their bifunctional activity and selectivity can be further amplified by (1) substituting "A" and "B" sites of pyrochlores (AA'BB'O7-x), (2) tuning metal oxidation states of A and B by varying synthesis conditions, and (3) modulating oxygen vacancy concentration, each of which yield favorable structural and electronic variations. In recent years, research on the synthesis and understanding of pyrochlores has significantly enhanced their viability, offering a new horizon in the quest for economical and active electrocatalysts. However, an account that focuses on critical developments in this field is still lacking.In this Account, we focus on the recent development of a variety of pyrochlore electrocatalysts to understand intrinsic structure-activity-selectivity-stability relationships in these materials. Recent developments and applications of pyrochlore-based electrocatalysts are discussed under the following headings: (1) modulation of crystal and electronic structure of pyrochlores, (2) structure-activity-stability relationships of different pyrochlores for OER and ORR, (3) development of OER-selective pyrochlores for brine electrolysis, and (4) the application of pyrochlores in electrochemical devices. Finally, we highlight some unaddressed issues such as the precise identification of active sites, which can be addressed in the future through advanced in situ and ex situ characterization techniques coupled with the density functional theory-based analyses. This Account provides foundational understanding to guide the comprehensive development of highly active, selective, stable and low-cost structurally engineered pyrochlores for high performance electrochemical devices.

A novel efficient electrocatalyst for oxygen reduction and oxygen evolution reaction in Li-O2 batteries: Co/CoSe embedded N, Se co-doped carbon

The research of highly efficient and large-capacity energy storage systems is the focus of the research community and the market. Lithium-oxygen (Li-O2) batteries have shown great potential as next generation secondary batteries since their energy density is comparable to that of gasoline. Herein, we report a three dimensional (3D) self-supporting Co-CoSe@NSeC/bioC cathode fabricated through growing cobalt based metal organic framework (ZIF-67) on biomass and subsequent high-temperature selenization. The as synthesized Co-CoSe@NSeC/bioC cathode, benefiting from the 3D porous structure, the active defects derived from the doping of N, Se heteroatoms in carbon skeleton, and the highly-active of Co/CoSe heterojunction, shows excellent oxygen reduction reaction/oxygen evolution reaction (ORR/OER) electrocatalytic activity. It delivers a high specific capacity of 9.1 mAh·cm−2 at a current density of 0.05 mA·cm−2 and maintains 78 stable cycles. The good performance of Co-CoSe@NSeC/bioC proves its potential as cathode for Li-O2 batteries.

Heterogeneous Bimetallic Organic Coordination Polymer-Derived Co/Fe@NC Bifunctional Catalysts for Rechargeable Li-O2 Batteries.

The Li-O2 battery has attracted substantial attention due to its high theoretical energy density. In particular, high-efficiency oxygen catalysts are very important for the design of practical Li-O2 batteries. Herein, we have synthesized heterogeneous crystalline-coated partially crystalline bimetallic organic coordination polymers (PC@C-BMOCPs), which are further pyrolyzed to obtain Co- and Fe-based nanoparticles embedded within rodlike N-doped carbon (Co/Fe@NC) as a bifunctional oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst used in the Li-O2 battery. Owing to excellent ORR/OER catalytic ability, the Co/Fe@NC bifunctional catalyst exhibits an efficient reversible reaction between O2 and Li2O2. Additionally, a large number of mesoporous channels are present in the core-shell Co/Fe@NC nanoparticles. These channels not only promote the diffusion of Li+ and O2, but also create ample room to store insoluble discharge product Li2O2. The Li-O2 batteries utilizing the bifunctional Co/Fe@NC oxygen electrode exhibit a large capacity of 17,326 mAh g-1, a long cycling life of more than 250 cycles, and excellent reversibility. This work provides a universally applicable strategy for designing nonnoble metal ORR/OER catalysts with excellent electrochemical performance for metal-air batteries.

Designing of Efficient Bifunctional ORR/OER Pt Single-Atom Catalysts Based on O-Terminated MXenes by First-Principles Calculations.

MXenes have been used as substrate materials for single-atom catalysts (SACs) due to their unique two-dimensional (2D) structure, high surface area, and high electronic conductivity. Oxygen is the primary terminating group of MXenes; however, all of the reported Pt SACs till now are fabricated with F-terminated MXenes. According to the first-principles calculations of this work, the failure of using O-terminated MXenes as substrates is due to the low charge density around Pt and C, which weakens the catalytic activity of Pt. By adjusting the electronic structure of M2C using a second submetal with a lower work function than M, 18 potential bifunctional Pt SACs are constructed based on O-terminated bimetal MXenes. After further consideration of some important practical application factors such as overpotential, solvation effect, and reaction barriers, only four of them, i.e., Cr2Nb2C3O2-VO-Pt, Cr2Ta2C3O2-VO-Pt, Cr2NbC2O2-VO-Pt, and Cr2TaC2O2-VO-Pt, are screened as bifunctional oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalysts. All of these screened SACs are originated from Cr-based MXenes, implying the significance of Cr-based MXenes in designing bifunctional Pt SACs.

Bifunctional Pt-IrO2 Catalysts for the Oxygen Evolution and Oxygen Reduction Reactions: Alloy Nanoparticles versus Nanocomposite Catalysts

In the present study, different concepts for the development of bifunctional oxygen reduction reaction/oxygen evolution reaction (ORR/OER) electrocatalysts are explored and compared. Bifunctional O...

Modular Design of Highly Active Unitized Reversible Fuel Cell Electrocatalysts

A modular, multicomponent catalyst design principle is introduced and exemplified using a three-component, oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst designed for the ox...

Influence of Additives on the Reversible Oxygen Reduction Reaction/Oxygen Evolution Reaction in the Mg2+ -Containing Ionic Liquid N-Butyl-N-Methylpyrrolidinium Bis(Trifluoromethanesulfonyl)imide.

The influence of different additives on the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) in magnesium‐containing N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([BMP][TFSI]) on a glassy carbon electrode was investigated to gain a better understanding of the electrochemical processes in Mg–air batteries. 18‐Crown‐6 was used as a complexing agent for Mg ions to hinder the passivation caused by their reaction with ORR products such as superoxide and peroxide anions. Furthermore, borane dimethylamine complex (NBH) was used as a potential water‐removing agent to inhibit electrode passivation by reacting with trace impurities of water. The electrochemical processes were characterized by differential electrochemical mass spectrometry to monitor the consumed and evolved O2 in the ORR/OER and determine the number of transferred electrons. Crown ether and NBH efficiently masked Mg2+. A stochiometric excess of crown ether resulted in reduced formation of a passivation layer, whereas at too high concentrations the reversibility of the ORR/OER was diminished.

Cobalt Nanoparticles Embedded Nitrogen-Doped Carbon Nanotubes as Bifunctional Catalysts for Flexible Solid-State Zn-Air Battery

Reasonable designing bifunctional catalyst based on non-precious metal materials for the durable oxygen reduction reaction/oxygen evolution reaction (ORR/OER) with high efficiency and sustainable economy is an attractive research topic toward flexible and rechargeable solid-state Zn-air batteries. In this paper, a novel one-dimensional cobalt nanoparticles embedded nitrogen-doped carbon nanotubes nanocomposite (Co-NC CNTs) was successfully prepared via a simple and inexpensive method to achieve the electrocatalyst containing Co nanoparticles with abundant reaction activated sites. The Co-NC CNTs directly function as a bifunctional and flexible catalyst with a remarkable electrochemical performance, including the relatively positive half-wave potential (0.82 V vs RHE) compared to the commercial platinum carbon (Pt/C) (0.84 V vs RHE) for ORR and the lower overpotential (0.46 V) compared to ruthenium oxide (RuO2) (0.4 V) for OER. Impressively, the assembled liquid rechargeable Zn-air batteries (ZABs) attain a peak power density of 115 mW cm−2 at the current density 194 mA cm−2 and a large special capacity (786.7 mAh g−1) as well as a better cycling stability of 150 cycles/50 h at 10 mA cm−2. A flexible solid-state Zn-air battery produced from Co-NC CNTs catalyst demonstrates the superior flexibility under bent condition at any angle and maintains the excellent stability.

Co-Ni Alloy Encapsulated by N-doped Graphene as a Cathode Catalyst for Rechargeable Hybrid Li-Air Batteries.

A hybrid Li-air battery uses a protected lithium anode and a porous air cathode in an aqueous electrolyte, based on a 4-e oxygen reduction reaction/oxygen evolution reaction (ORR/OER). It avoids the insoluble and insulating Li2O2 product in a typical nonaqueous Li-air battery, and it owns unique advantages. A bifunctional cathode catalyst is crucial to battery performance. Here, we synthesize an ultrathin N-doped graphene-encapsulated nanosphere Co-Ni alloy (Co-Ni@NG). It has hierarchical architecture consisting of a uniform Co-Ni nanoalloy coated with a thin layer of N-doped graphene, showing high activity, high stability, and lower overpotential between the ORR and OER (0.55 V between onset potentials). It exhibited a discharge/charge voltage gap of 0.55 V at a current density of 1.4 mA cm-2, which is much smaller than the commercial Pt/C catalyst. It delivered an energy density of 3158 Wh kg-1 and a power density as high as 134.2 W m-2 at a current density of 7 mA cm-2. The graphene shells protect the alloy catalyst and improve the durability of the catalyst. One hundred cycles were demonstrated without significant deterioration. It was testified as a promising energy storage system with high energy density, efficiency, reliability, and durability.

The ORR and OER Performances of Bismuth Ruthenate As the Cathode of Air Battey Using KOH Solution

Electrochemical power sources that use oxygen as a reactant may play an essential role in the future energy needs of the society. Fuel cells, aqueous metal-air batteries, and metal hydride (MH)/air batteries hold promise as the power sources. Especially, for rechargeable batteries, an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) are the cathode reactions during charge and discharge. Therefore, the development of highly active catalysts (i.e., low activation overpotential) for the reactions is required and remains challenging. Then, we attempted to develop the electrode catalysts which decrease in the overpotential for ORR and OER in an alkaline aqueous solution. Especially, we focus on the pyrochlore type metal oxide including bismuth and ruthenium ions as Bi2Ru2O7 (BRO) and evaluated the overpotential and Tafel slopes for both ORR and OER by using the rotating ring-disk electrode (RRDE) technique as well as a half-cell test. We also have investigated the effect of aluminum ion addition to BRO, which is called as ABRO, by the addition of aluminium nitrate [Al(NO3)3] during the synthesis of BRO. BRO and ABRO were prepared by a precipitation method. In order to prepare BRO, the method is denoted bellow. At first, Bi(NO3)3 and RuCl3 aqueous solutions were separately prepared and well mixed in a 1 : 1 molar ratio. The mixture solution was heated up to 75 oC and stirred for 1 hour. Then, NaOH aqueous solution was added to the mixed solution to produce a precipitate and stirred for 72 hour. After that, the precipitate was made for calcination under atmospheric air at 500 and 600oC for 3 hours and then it was washed with pure water and dried at 120 oC for 3 hours. On the other hand, Al(NO3)3 was also added to the mixture solution during the synthesis to investigate an effect of aluminum ion on the ORR and OER of BRO. These products were obtained after the calcination at the desired temperatures as 500 and 600oC in air. X-ray diffraction (XRD) and Field emission scanning electron microscope (FE-SEM) observation were performed for characterization. The catalytic behavior was investigated by a RRDE. The disk and ring electrodes were made by titanium (Ti) and Pt, respectively. BRO or ABRO powder was loaded on Ti disk. Hg|HgO reference electrode and a Ni mesh counter electrode were used. The electrochemical cell was made of polytetrafluoroethylene (PFA). The electrolyte was 0.1 mol dm-3 KOH aqueous solution. We also measured constant current charge-discharge measurements to evaluate BRO as the cathode catalyst for the air-battery. In this test, 6.0 mol dm-3 KOH aqueous solution was used as the electrolyte. The peaks in the XRD patterns of BRO were assigned to Bi2Ru2O7, when the calcination temperature was 500oC; on the other hand, the peaks were assigned to Bi1.87Ru2O6.903 when the calcination temperature was 600oC. In addition to these, tiny diffraction peaks of Bi2O3 were also confirmed. These results indicated that both of oxygen and bismuth were decreased between 500oC and 600oC due to the elimination of oxygen from BRO. In the case of ABRO, the peaks were assigned to Bi1.87Ru2O6.903 at 500oC and to Bi1.88Ru2O6.906 at 600oC and simultaneously, Al2O3 was also confirmed in both cases. Table 1 shows the overpotentials and Tafel slopes for ORR and OER of BRO and ABRO. The overpotentials and Tafel slopes for OER of BRO@500oC were around 0.14 V and 70 mV dec.-1, respectively. The overpotential was increased when the calcination temperature was at 600oC, but the Tafel slope was unchanged. The overpotential of ABRO for OER was estimated at 0.11 V, which shows that the aluminium nitrate addition would be effective to decrease in the overpotential. In this presentation, we will report the catalyst performances during the constant current charge-discharge measurements as the air-battery. This work was supported by “Development of Hydrogen|Air battery”, “Advanced Low Carbon Technology Research and Development Program (ALCA)” of Japan Science and Technology Agency (JST). Table 1 The overpotentials and Tafel slopes for ORR and OER of BRO and ABRO. Sample Overpotential / V Tafel slope / mV dec.-1 ORR OER ORR OER BRO@500 0.34 0.14 -69 71 BRO@600 0.33 0.19 -64 74 ABRO@500 0.37 0.11 -51 62 ABRO@600 0.35 011 -41 41

High-performing rechargeable/flexible zinc-air batteries by coordinated hierarchical Bi-metallic electrocatalyst and heterostructure anion exchange membrane

Due to the lack of highly efficient and low-cost oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst and alkaline anion exchange membrane (AEM), advanced rechargeable zinc-air batteries are largely hindered in many applications from wearable electronics to electric vehicles. Herein, a hybrid of porous Co3O4 anchoring on MnO2, then interpenetrating with CNTs (Co3O4/MnO2-CNTs) is synthesized via facile hydrothermal process, and an AEM (CS/EMImC-Co-EP/GO) employing semi-interpenetrating network structure is fabricated with a simple solution-casting method. The porous nanoparticles and chrysalis-like hybrid as well as strong bi-metallic coupling effect build highways and buffer zones for reactant and electrons transfer for ORR/OER. In addition, due to the competition of bottom Co atoms, the density functional theory (DFT) proves that the neighbor Mn sites (Mn1 and Mn2) of the MnO2(110) surface are evidently activated, which prompts the catalytic activity of hybrids by making the Mn1, Mn2 3d density of states move forward lower energy entirely. As a result, Co3O4/MnO2-CNTs exhibit superior ORR/OER activities with the low potential difference (ΔE) of 0.85 V and impressive performances in rechargeable aqueous zinc-air batteries (power density: 534 mW cm−2). Moreover, combining AEM integrated into rechargeable flexible all-solid-state zinc-air batteries and stack, the enhancement natures of wearable devices are achieved even under different bending angles benefiting from high hydroxyl anion conductivity and remarkable flexibility of AEM semi-interpenetrating network, which accelerates ion transport by the synergy of hopping and vehicle mechanisms. Furthermore, the flexible all-solid-state zinc-air batteries show excellent tolerance toxicity of CO2.

The electronic structure underlying electrocatalysis of two‐dimensional materials

AbstractThe understanding and development of advanced electrochemical catalysts have attracted intensive studies and achieved tremendous progress in the past decades. Two‐dimensional (2D) materials, such as doped graphene and atomically‐thin transition metal compounds, have shown great promise as electrocatalysts for various renewable energy conversion and storage reactions. Their further developments require improved understanding of the catalytic mechanisms at atomic level. Currently, most of the understandings are based on the formation free energies of the intermediates, which are determined by their binding strengths with the catalyst, usually calculated from density functional theory (DFT). These energies/binding strengths have been used as descriptor to describe the activity of many catalysts. However, it remains less explored why different catalysts have different binding strengths and what are the underlying factors controlling them, requiring studies going beyond atomic level to electronic level. This review aims to provide such links, focusing on 2D electrocatalysts for hydrogen evolution reaction (HER), oxygen reduction reaction/oxygen evolution reaction (ORR/OER), CO2 reduction reaction (CO2R) and nitrogen reduction reaction (NRR). We also discuss some of the significant issues that need to be addressed in DFT calculations, including the effects of varying charge and fixed potential of the catalyst, the passivation of active sites, and the solvation effects.This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis Structure and Mechanism > Computational Materials Science

Novel and highly efficient cathodes for Li-O2 batteries: 3D self-standing NiFe@NC-functionalized N-doped carbon nanonet derived from Prussian blue analogues/biomass composites

Traditional 3D self-standing electrodes for lithium-oxygen (Li-O2) batteries require a high cost and complex preparation process that restrict their development. Herein, discarded biomass (pomelo peel, PP) is used as raw material and in-situ grew NiFe-Prussian blue analogues on its surface. Then a novel 3D binder-free and self-standing NiFe@NC/PPC electrode is obtained through the carbonization process and directly used as a cathode in Li-O2 batteries.Compared with PPC (carbonized pomelo peel) and NiFe@NC/CP (NiFe@NC catalysts coated on carbon paper), NiFe@NC/PPC gathered the advantageous characteristics of i) efficient diffusion rates for O2/electrolyte and ii) good catalytic activity for oxygen reduction reaction/oxygen evolution reaction (ORR/OER). The as fabricated Li-O2 batteries, with NiFe@NC/PPC as cathode, are performed a relatively high specific capacity (13.79 mAh cm−2), a long cycle life (290 cycles) at a current density of 0.1 mA cm−2. Therefore, considering the convenience of synthesis method and the inexpensive raw materials, this is a feasible way to prepare high performance and low cost cathodes for Li-O2 batteries.