High Working Potential Research Articles

NaF-rich interphase and high initial coulombic efficiency of red phosphorus anode for sodium-ion batteries by chemical presodiation.

Red phosphorus/carbon (P/C) materials have been extensively studied as promising anodes for sodium-ion batteries (SIBs) owing to their high capacities and moderate working potentials. However, the low initial Coulombic efficiency (ICE) and unstable solid-electrolyte interphase (SEI) of P/C composites limit their widespread applications. In this study, we develop an effective presodiation method to compensate for the irreversible sodium loss of the S-doped P/C (P/C@S) anode and yield a thin, uniform, and NaF-rich SEI layer on the presodiated P/C@S (pNa-P/C@S) anode during cycling. Consequently, the pNa-P/C@S anode exhibits a remarkable ICE of 98.7% as well as superior cycling performance and rate capability in the half cell. When pNa-P/C@S anode is coupled with conventional Na3V2(PO4)2F3, Na3V2(PO4)3, and NaCu0.12Ni0.23Fe0.33Mn0.33 cathodes, all the full cells demonstrate desirable ICEs (>98%), high energy densities, and excellent cycling performance. The proposed method has been extended to another anode (SnO2) to demonstrate its applicability in fabricating anodes with a high ICE and stable NaF-rich SEI layer.

Enhanced electrochemical performance of LiVPO4F/C composite with in-situ generated Li3V2(PO4)3 for lithium-ion batteries

The vanadium-containing phosphate polyanion LiVPO4F has been attractive as a novel 4 V cathode for lithium-ion batteries. Herein, a hybrid cathode containing two active components of LiVPO4F and Li3V2(PO4)3 was successfully obtained by single-step solid-state reaction. The crystalline grains are coated by an amorphous carbon layer of about 8 nm thick. The composite presents reversible capacities of 102.8 and 98.2 mAh g−1 at the rates of 10C and 20C, respectively. Even at an ultrahigh rate of 100C (14.5 A g−1), it remains a discharge capacity of 70.1 mAh g−1 with a high average working potential of 3.5 V. After cycled 500 times at 10C, the obtained sample shows a capacity retention of 78.6%, implying outstanding cycling performance. The electrochemical impendence spectroscopy demonstrates that the hybrid cathode delivers higher lithium-ion diffusion coefficient. It is believed that the electrochemical performance is enhanced synergistically by the in-situ generated ionic conductor of Li3V2(PO4)3. Finally, when charged and discharged at around 4.1 V, the intermediate phase of LixVPO4F is clearly revealed by CV tests, which likely derives from a symmetry phase transform mechanism.

A Ternary Additive Mixture for Suppressed Electrolyte Decomposition and Mitigated Gassing in 5V Lnmo‖Graphite Li-Ion Cells

The cobalt-free spinel LiNi0.5Mn1.5O4 (LNMO) represents a promising candidate for more sustainable high-energy lithium-ion cathodes due to its high operating voltage (4.7 V vs. Li+/Li), low cost and environmental impact, especially when processed in aqueous suspension with water-soluble binders.[1,2] Although the intrinsic properties of the material are already studied extensively and understood quite well, the high working potential still poses challenges for LNMO-comprising lithium-ion battery cells, which need to be addressed before the material can be successfully commercialised. This specifically includes the decomposition of the electrolyte at high potentials and the dissolution of transition metal (TM) ions from the positive electrode and their migration to the negative electrode.[1,3] The latter leads to accelerated electrolyte decomposition also on the anode side and an overall increased gas formation inside the cell.[4] Besides the modification of the material and its surface itself, one of the most promising approaches is the use of electrolyte additives, since this is easy to implement and, therefore, also cost effective. Such additives can be designed to extend the electrochemical stability window, to stabilise the electrode|electrolyte interphases and/or to scavenge harmful species inside the electrolyte.[5–7] The ternary mixture introduced herein decomposes preferentially on both electrodes leading to improved interfacial stability, which is directly reflected in an increased cycling performance of true 5V LNMO‖graphite Li-ion cells – also at elevated temperatures. An in-depth XPS analysis unveiled the growth and composition of a stable interphase layer and showed that this limits the amount of TM deposits on the anode. Finally, in order to demonstrate the beneficial impact also in terms of commercial applicability, the gassing behaviour was investigated qualitatively by differential electrochemical mass spectrometry (DEMS) and quantitatively by exploiting Archimedes’ principle to determine the gas volume formed operando during the cycling of LNMO‖graphite pouch cells.[1] G. Liang, V. K. Peterson, K. W. See, Z. Guo, W. K. Pang, J. Mater. Chem. A 2020, 8, 15373–15398.[2] M. Kuenzel, D. Bresser, T. Diemant, D. V. Carvalho, G. T. Kim, R. J. Behm, S. Passerini, ChemSusChem 2018, 11, 562–573.[3] J. H. Kim, N. P. W. Pieczonka, L. Yang, ChemPhysChem 2014, 15, 1940–1954.[4] B. Michalak, B. B. Berkes, H. Sommer, T. Brezesinski, J. Janek, J. Phys. Chem. C 2017, 121, 211–216.[5] M. Y. Abeywardana, N. Laszczynski, M. Kuenzel, D. Bresser, S. Passerini, B. Lucht, Int. J. Electrochem. 2019, 2019, 1–7.[6] M. S. Milien, H. Beyer, W. Beichel, P. Klose, H. A. Gasteiger, B. L. Lucht, I. Krossing, J. Electrochem. Soc. 2018, 165, A2569–A2576.[7] A. Kazzazi, D. Bresser, M. Kuenzel, M. Hekmatfar, J. Schnaidt, Z. Jusys, T. Diemant, R. J. Behm, M. Copley, K. Maranski, J. Cookson, I. de Meatza, P. Axmann, M. Wohlfahrt-Mehrens, S. Passerini, J. Power Sources 2021, 482, 228975.

Metal (Cu/Fe/Mn)-Doped Silicon/Graphite Composite as a Cost-Effective Anode for Li-Ion Batteries.

Silicon is a worthy substitute anode material for lithium-ion batteries because it offers high theoretical capacity and low working potentials vs. Li+/Li. However, immense volume changes and the low intrinsic conductivity of Si hampers its practical applications. In this study, nano/micro silicon particles are achieved by ball milling silicon mesh powder as a scalable process. Subsequent metal (Cu/Fe/Mn) doping into nano/micro silicon by low-temperature annealing, followed by high-temperature annealing with graphite, gives a metal-doped silicon/graphite composite. The obtained composites were studied as anodes for Li-ion batteries, and they delivered high reversible capacities of more than 1000 mAh g−1 with improved Li+ diffusion properties. The full cells from these composite anodes vs. LiCoO2 cathodes delivered suitable energy densities for Li+ storage applications. The enhanced electrochemical properties are accredited to the synergistic effect of metal doping and graphite addition to silicon and exhibit potential for suitable Li+ energy storage applications.

A comprehensive review study on pure titanium niobium oxide as the anode material for Li-ion batteries

Li-ion batteries (LIBs) are in increasing demand due to their application in a large variety of fields such as portable electronic devices and electric vehicles. However, the development of high-performance electrode materials with a long lifetime, excellent rate capability, and high safety is considered as a significant challenge in the advancement of LIBs. Recently, titanium niobium oxide (TNO) compounds have been considered as one of the most promising intercalation-type anode materials and highly potential alternatives to commercial graphite and Li4Ti5O12 anodes. This family of materials possess high theoretical capacities (377–402 mAh/g) resulting from their multiple redox couples (Ti4+/Ti3+, Nb5+/Nb4+, Nb4+/Nb3+), high safety, low volume changes during cycling, high working potential, and excellent cyclic stability. However, their low electronic/ionic conductivities would result in their poor rate performance. Various strategies such as ion doping, composite preparation with conductive materials, dimensional/morphological controlling, and defective structure engineering design have been proposed to improve the rate performance of TNO materials. In this review study, dimensional/morphological controlling, and defective structure engineering approaches are reviewed for enhancing the electrochemical properties of pure TNO anodes. In this context, the detailed findings of the most important recent literature on TNO anode materials are reviewed, from their optimal synthesis parameters, and the obtained morphological/structural features to their electrochemical properties. Furthermore, the challenges to the practical use of TNO anodes in full-cell LIBs are presented. Finally, the research gaps and the future perspective are proposed.

Non-aqueous rechargeable calcium-ion batteries based on high voltage zirconium-doped ammonium vanadium oxide cathode

Calcium-ion batteries heed the research attention as a energy storage system due to the merits of natural abundance, low-cost, reduction potential (−2.87 V vs. SHE) similar to lithium (−3.04 V vs. SHE) and high theoretical working potential of calcium. However, the practical realization experiences a barrier due to the lack of suitable high-voltage positive electrodes to accommodate the large Ca 2+ with sufficiently fast ionic conduction. Herein, we investigate the zirconium-doped ammonium vanadium oxide (Zr–NH 4 V 4 O 10) as a high-voltage cathode for the rechargeable calcium-ion batteries for the first time at room temperature. It exhibited an initial discharge capacity of 78 mAh g −1 with an average discharge voltage of ∼3.0 V vs. Ca 2+ |Ca and delivered an initial energy density of 231 W h kg −1 in calcium triflate [Ca(CF 3 SO 3) 2 ] added in propylene carbonate electrolyte. Moreover, the Zr–NH 4 V 4 O 10 host presents a high-rate capability, excellent cycling stability (0.021% capacity decay per cycle) for 500 cycles with ∼89% capacity retention, maintaining ∼100% Coulombic efficiency. This is one of the first demonstrations of reversible Ca-ion storage with a high voltage (∼3.0 V) using a conventional electrolyte.

One-step multiple structure modulations on sodium vanadyl phosphate@carbon towards ultra-stable high rate sodium storage

• A template-assisted sol–gel strategy is proposed for multi-structure engineering of NVP@C cathode material. • Simultaneous realizations of pore constructing, nanosizing and carbon compositing can be achieved in one step. • Pore structure of NVP@C can be tuned by adjusting the diameter of PS nanospheres. • A novel mesoporous-macroporous structure can be realized due to the demulsification of PS emulsion. • The mesoporous-macroporous NVP@C exhibits extraordinary rate capability and cycling stability at high rate. Na 3 V 2 (PO 4 ) 3 (NVP) is recognized as a promising sodium ion battery (SIB) cathode material due to its high working potential and robust three-dimensional framework. However, the poor intrinsic electronic conductivity and huge volume change during sodium ion insertion/desertion process hinder its further applications, which makes its structure modulations highly desirable. Herein, a facile template-assisted sol–gel strategy is developed to realize multiple structure modulations of NVP@C in one-step. With citric acid as chelating agent and polystyrene (PS) nanospheres as template, the realization of nanosizing NVP particles, hybridizing NVP particle with carbon material and constructing pore structure on NVP@C can be facially achieved. More importantly, the pore structure can be tuned by the diameter of used PS nanospheres. When the diameter of PS nanospheres is down to 70 nm, the corresponding 70-PS NVP possesses a hierarchically mesoporous-macroporous structure due to the demulsification effect, which can shorten the ion diffusion pathway, increase the contact surface area between the electrolyte and active material, improve the diffusion kinetics and buffer the volume change. Benefiting from the above superiority, the sample exhibits an extraordinary rate capability and a prominent cycling stability at high rate (104 mAh g −1 after 5000 cycles at 50C), which surpass most of the recently reported SIB cathode materials. This work opens a facile revenue for boosting the electrochemical performance of electrode materials through characteristic pore construction, nanosizing and integration with carbonaceous materials.

3D LiMn2 O4 Thin Film Deposited by ALD: A Road toward High-Capacity Electrode for 3D Li-Ion Microbatteries.

Miniaturized electronics suffer from a lack of energy autonomy. In that context, the fabrication of lithium-ion solid-state microbatteries with high performance is mandatory for powering the next generation of portable electronic devices. Here, the fabrication of a thin film positive electrode for 3D Li-ion microbatteries made by the atomic layer deposition (ALD) method and in situ lithiation step is demonstrated. The 3D electrodes based on spinel LiMn2 O4 films operate at high working potential (4.1 V vs Li/Li+ ) and are capable of delivering a remarkable surface capacity (≈180 μAh cm-2 ) at low C-rate while maintaining more than 40 μAh cm-2 at C/2 (time constant = 2 h). Both the thickness of the electrode material and the 3D gain of the template are carefully tuned to maximize the electrode performance. Advanced characterization techniques such as transmission electron and X-ray transmission microscopies are proposed as perfect tools to study the conformality of the deposited films and the interfaces between each layer: no interdiffusion or segregation are observed. This work represents a major issue towards the fabrication of 3D-lithiated electrode by ALD-without any prelithiation step by electrochemical technique-making it an attractive solution for the fabrication of 3D Li-ion solid-state microbatteries with semiconductor processing methods.

WO3-x@W2N heterogeneous nanorods cross-linked in carbon nanosheets for electrochemical potassium storage

Potassium-ion batteries (PIBs) are highly desirable as large-scale sustainable battery systems due to the high working potential and low-cost potassium resources. However, the large radius of potassium ion inevitably causes huge volume expansions and rapid capacity decay of electrodes, so the development of long-life anodes still remains at its infancy. Herein, the nonstoichiometric heterostructures with bimetallic characteristics (WO3-x@W2N) are rationally constructed on mono-faceted nanorods and in-situ cross-linked in nitrogen-doped carbon nanosheets (WO3-x@W2N/CNSs). The mono-faceted WO3-x nanorods endow oxygen vacancies with abundant unsaturated active sites and dangling bonds in their directional charge-transfer paths. The heterostructures with rich self-built electric fields can regulate electronic structures of oxygen-vacancy/metallic WO3-x and metallic W2N, and notably enhance the efficiency of charge transfer and storage under the protection of highly conductive CNSs. Utilizing the vacancy, phase and interface engineering, the WO3-x@W2N/CNSs deliver a large reversible capacity (366.6 mAh g−1 at 0.1 A g−1), with high-rate capacity and ultralong lifespan (113.2 mAh g−1 after 12,000 cycles at 10.0 A g−1). These findings, storage mechanisms and kinetics behaviors are elucidated in detail via the advanced techniques and first-principles calculations, demonstrating that the nonstoichiometric and metallic heterostructures have promising potentials in high-performance metal ion batteries.

Knitting a sweater with UV-induced in situ polymerization of poly(pyrrole-co-citral nitrile) on Ni-rich layer oxide cathode materials for lithium ion batteries

Ni-rich layered oxide (LiNi0.8Co0.1Mn0.1O2) has become popular commercial cathode material for lithium ion batteries, due to its high working potential and high specific capacity. It is still a challenge, however, to maintain the structure and performance under extreme conditions, such as at high charging cutoff (≥4.5 V), high temperature (≥60 °C) and higher charge-discharge rate (≥3 C). Herein, Poly (pyrrole-co-citral nitrile) (PPC) optimized interfacial layer is designed and constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by an in situ photopolymerization self-assembly technology. The sweater-like co-polymer coating provides an integral protection from side reaction, particle rupture and irreversible phase transition during cycling under the extreme conditions. Furthermore, the delocalized π bonds and cross-linked network structure of the co-polymer coating ensure the efficient and stable interface between electrolyte and electrode. This work offers a novel and useful strategy to enhance the electrochemical performance of Ni-rich cathode materials for high-energy lithium ion batteries at extreme conditions.

Ultrastable dihydrophenazine-based polymer from industrial waste as a sustainable lithium-ion battery cathode material

An industrial-waste-derived polymer, PBMEP, was effectively synthesized as a superior sustainable LIB cathode material with robust cycling stability, high working potentials, and excellent rate capability.

Accelerating Anode Reaction with Electro-oxidation of Alcohols over Ru Nanoparticles to Reduce the Potential for Water Splitting.

Generating hydrogen by water electrolysis is a promising and sustainable approach to the production of a green energy carrier, but the sluggish kinetics of the oxygen evolution reaction (OER) at anode leads to a high working potential. Replacing OER with electro-oxidation of organics driven at a low potential offers an effective way to accelerate the sluggish anode reaction, and thus increase hydrogen evolution in water-splitting. Herein, we have prepared a Ru nanoparticles on N-doped carbon nanotubes (Ru-NPs@NCNTs) to implement electro-oxidation of benzyl alcohol toward reducing the anodic potential in watersplitting. The potential of the anode reaction is remarkably decreased from 1.76 to 1.19 V vs RHE at a current density of 10 mA cm-2 with the assistance of a Ru-NPs catalyst. Furthermore, 100% selectivity and 95% yield of valuable benzaldehyde were achieved simultaneously. The Ru-NPs also exhibits good durability and wide applicability to other alcohols. The high performance of Ru-NPs is mainly attributed to the unique horizontal adsorption configuration of benzyl alcohol with surface atoms of the catalyst, shortening the distance between the •OH group and Ru atoms, and increasing the activation rate of the •OH group. This work presents a feasible strategy to boost water-splitting performance and concurrently produce value-added organics under mild conditions.

Reversible anion intercalation into graphite from aluminum perchlorate “water‐in‐salt” electrolyte

Anion intercalated graphite has achieved tremendous attention for the application as cathode materials in dual-ion batteries due to their high working potentials, reversibility, and low cost. However, the process of anion intercalation into graphite requires high oxidative stability of the electrolytes and high reaction potentials above 1.4 V vs. Ag/AgCl (4.5 V vs. Li+). Reaching such high potentials is difficult with conventional aqueous electrolytes due to their limited electrochemical window. Here, we demonstrate a highly concentrated “water-in-salt” electrolyte of aluminum perchlorate that demonstrates a wide electrochemical stability window of 4.0 V. The “water-in-salt” electrolyte suppresses the dissociation of water at high potentials, facilitating a stable and reversible perchlorate (ClO4−) anion intercalation into the graphite with a Coulombic efficiency of over 95% for more than 2000 cycles. The structural and chemical changes of the anion-intercalated graphite are studied by Operando Raman, Operando X-ray diffraction, and X-ray photoelectron spectroscopy. Our study provides an insight into ClO4− anion intercalation into graphite in the supersaturated aluminum perchlorate “water-in-salt” electrolyte, demonstrating a suitable platform for future high-voltage aqueous energy storage systems.

Sputtering Coating of Lithium Fluoride Film on Lithium Cobalt Oxide Electrodes for Reducing the Polarization of Lithium-Ion Batteries.

Lithium cobalt oxide (LCO) is the most widely used cathode materials in electronic devices due to the high working potential and dense tap density, but the performance is limited by the unstable interfaces at high potential. Herein, LiF thin film is sputtered on the surface of LCO electrodes for enhancing the electrochemical performance and reducing the voltage polarization. The polarization components are discussed and quantified by analyzing the relationship between electrochemical polarization and charger transfer resistance, as well as that between concentration polarization and Li-ion diffusion coefficients. In addition, the decreased charge transfer resistance, increased lithium-ion diffusion coefficients, and stabilized crystal structure of LiF-coated LCO are confirmed by various electrochemical tests and in-situ XRD experiments. Compared to that of pristine LCO, the capacity and cycling performance of LiF-coated LCO is improved, and the overpotential is reduced upon cycling. This work provides reference for quantifying the various polarization components, and the strategy of coating LiF film could be applied in developing other analogous cathode materials.

Nano Silicon Composite with Gelatin/Melamine Derived N-doped Carbon as an Efficient Anode Material for Li-ion Batteries

Silicon (Si) has a high theoretical capacity and low working potential vs. Li/Li<sup>+</sup>, and has been investigated as the most capable negative electrode material for lithium-ion batteries (LIBs). However, Si undergoes significant volume changes during the Li<sup>+ </sup>alloying/ dealloying processes, leading to unstable cycle life and limiting its practical applicability in anodes. Introducing carbon into the Si anodes can effectively address the Si drawbacks, while providing advantages of improved conductivity and structural stability. In this study we choose gelatin/ melamine combination as an eco-friendly and cost-effective source for nitrogendoped carbon to make a Si composite. The prepared composite was studied as an anode material for LIBs, and it delivered excellent cyclability with 2175 mAh g<sup>-1</sup> capacity after 50 cycles with 86% capacity retention at 200 mA g<sup>-1</sup>. The composite exhibited superior rate capability and improved Li<sup>+</sup> diffusion properties compared with bare Si nanoparticles (Si NP). The significant enhancement could be attributed to the structural stability and conductivity provided by the nitrogen-doped carbon matrix. This work promotes emerging batteries with low-cost materials as a promising solution for increasing energy storage requirements.

In situ polyaniline coating of Prussian blue as cathode material for sodium-ion battery.

Prussian blue (PB) has great potential for use as a sodium cathode material owing to its high working potential and cube frame structure. Herein, this work reports a two-step method to synthesize PB with ascorbic acid as the ball-milling additive, which improves the electrochemical rate performance of PB during the traditional co-precipitation method. The obtained PB sample exhibited a superior specific capability (113.3 mAh g−1 even at 20 C, 1 C = 170 mA g−1) and a specific capacity retention of 84.8% after 100 cycles at 1 C rate. In order to enhance the cycling performance of the PB, an in situ polyaniline coating strategy was employed in which aniline was added into the electrolyte and polymerized under electrochemical conditions. The coated anode exhibited a high specific capacity retention of 62.7% after 500 cycles, which is significantly higher than that of the non-coated sample, which only remains 40.1% after 500 cycles. This development has shown a great potential as a low-cost, high-performance and environment-friendly technology for large-scale industrial application of PB.

Utilization of the V5+/V4 + Redox Reaction in Nasicon-Structured Cathode Materials for Sodium-Ion Batteries

The energy problem has become a critical issue worldwide, and renewable energy will dominate the energy system in the near future. Electrochemical storage devices are widely used as the energy storage devices of renewable energy, and the most intuitive feeling is that electric vehicles driven by lithium-ion batteries (LIBs) have become a new generation of transportation. Nevertheless, the worrisome side though was the high cost of LIBs and the scarcity of lithium. Considering that high crustal abundances of sodium and large-scale energy storage devices are almost not restricted by the size of the device, sodium-ion batteries (SIBs) were considered as a promising alternative to the LIBs.1 Cathode materials, as the highest cost proportion of SIBs (32.4 %), have always been the bottleneck of development and high-performance cathode materials are actively being explored by researchers. Sodium super ionic conductor (NASICON)-structured materials, as a member among the most investigated cathode materials for SIBs, are a promising candidate due to the excellent stability of long-term cycling.Na3V2(PO4)3 is the most classical cathode material in NASICON-structures with the high working potential (3.4 V, corresponding to the V4+/V3+ redox reaction) and high specific capacity (117.6 mAh g-1). Recently, many studies have shown that the V5+/V4+ redox reaction can be accessed through partial substitution of V3+.2 However, two phenomena needed deep consideration: (1) the potential of the V5+/V4+ redox reaction in Na3V2(PO4)3 is different from its derivatives, and (2) the utilization of the V5+/V4+ redox reaction is very limited. In one of our work, Na3VAl(PO4)3 and Na3VGa(PO4)3 cathode materials were selected as contrasting systems to explain these two phenomena because Al and Ga are in the same group. Combining experimental tests and density functional theory (DFT) calculations, sodium ions are extracted/inserted from/into different sodium sites, causing a different potential of the V5+/V4+ redox reaction; and the full use of the V5+/V4+ redox reaction was restricted by the excessive diffusion energy barrier.3 Therefore, we proposed two possible approaches to promote the V5+/V4+ redox reaction: (1) substitution of V3+ with smaller ions and (2) utilizing the x = 2.0-3.0 region.As described previously, the access of V5+/V4+ redox reaction is difficult. Reducing the amount of substitution is an effective method to fully use of the V5+/V4+ redox reaction. We have studied successively the electrochemical properties of Na3V1+x Cr1-x (PO4)3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5),4 Na3V1+x Al1-x (PO4)3 (x = 0.3, 0.5 and 0.7) and Na3V1+x Ga1-x (PO4)3 (x = 0.5 and 0.8). To sum up, Na3V1.7Al0.3(PO4)3 has a good trade-off in utilization of the V5+/V4+ redox reaction and the V4+/V3+ redox reaction. The reversible specific capacity of Na3V1.7Al0.3(PO4)3 is 105.8 mAh g-1 in the first cycle and the specific capacity retention is 95.6 % after 50 cycles at 20 mA g-1.References Goikolea, E.; Palomares, V.; Wang, S.; Larramendi, I. R.; Guo, X.; Wang, G.; Rojo, T., Na‐Ion Batteries—Approaching Old and New Challenges. Advanced Energy Materials 2020, 10 (44), 2002055. Gao, H.; Seymour, I. D.; Xin, S.; Xue, L.; Henkelman, G.; Goodenough, J. B., Na3MnZr(PO4)3: A High-Voltage Cathode for Sodium Batteries. J. Am. Chem. Soc. 2018, 140 (51), 18192-18199. Wang, Q.; Gao, H.; Li, J.; Liu, G. B.; Jin, H., Importance of Crystallographic Sites on Sodium-Ion Extraction from NASICON-Structured Cathodes for Sodium-Ion Batteries. ACS Appl Mater Interfaces 2021, 13 (12), 14312-14320. Wang, Q.; Zhao, Y.; Gao, J.; Geng, H.; Li, J.; Jin, H., Triggering the Reversible Reaction of V3+/V4+/V5+ in Na3V2(PO4)3 by Cr3+ Substitution. ACS Appl Mater Interfaces 2020, 12 (45), 50315-50323. Figure 1

On the Durability of Iridium‐Based Electrocatalysts toward the Oxygen Evolution Reaction under Acid Environment

AbstractProton exchange membrane water electrolyzers (PEMWEs) driven by renewable electricity provide a facile path toward green hydrogen production, which is critical for establishing a sustainable hydrogen society. The high working potential and the corrosive environment pose severe challenges for developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER). To date, iridium (Ir)‐based materials, largely metallic Ir and Ir‐based oxides, are the most suitable OER electrocatalysts for PEMWEs due to their balanced activity and durability. Tremendous efforts have been devoted to improving the specific activity of Ir species to reduce the cost; however, advances in enhancing the durability of Ir‐based electrocatalysts are rather limited. In this review, the recent research progress on tackling the stability issues of Ir‐based OER electrocatalysts in acid media is summarized, aiming to provide inspiration for designing highly active and stable Ir‐based electrocatalysts. The OER mechanism and the associated failure modes of active Ir species are summarized. Then, mechanistic studies on the dissolution behavior of Ir species and experimental attempts on enhancing the durability of Ir‐based electrocatalysts are discussed. The personal perspectives for future studies on Ir‐based OER electrocatalysts are also provided.

Electronic configuration of single ruthenium atom immobilized in urchin-like tungsten trioxide towards hydrazine oxidation-assisted hydrogen evolution under wide pH media

Replacing sluggish oxygen evolution reaction (OER) by hydrazine oxidation reaction (HzOR) is an energy-saving approach to assist alkaline overall water splitting (OWS). However, it is still at the infant stage as the unsatisfactory of the design strategies for bifunctional catalysts toward both HzOR and hydrogen evolution, which leads to high working potential compared to the theoretical value. Here, for the first time, we report a galvanostatic immobilization of ruthenium single atoms (Ru SAs) into the oxygen vacancy of urchin-like tungsten trioxide (Vo-WO3) and show low overpotentials of 17, 34, and 64 mV at –10 mA cm–2 under acid, alkaline, and neutral H2 evolution, respectively. As an efficient bifunctional catalyst, the Vo-WO3/Ru SAs is firstly introduced to HzOR and achieves low working potential of –58 mV at 10 mA cm–2. The HzOR-assisted OWS also delivers an ultralow cell voltage of only 25 mV at 10 mA cm–2 in alkaline medium, which is far beyond the platinum and most of the state-of-the-art catalysts. Additionally, this coupled system can also be well performed under neutral condition, realizing a cell voltage of only 137 mV at 10 mA cm–2. The excellent pH-universal HzOR-assisted OWS activity is attributed to the particular electronic configuration between Ru SAs and WO3, the immobilization of Ru SAs in WO3 could induce electron redistribution and optimize free energy of hydrogen adsorption in hydrogen evolution, while the isolation of Ru SAs also leads to the electropositivity of W sites and tends to accelerate the oxidation of hydrazine.

Revealing the Dynamics and Roles of Iron Incorporation in Nickel Hydroxide Water Oxidation Catalysts.

The surface of an electrocatalyst undergoes dynamic chemical and structural transformations under electrochemical operating conditions. There is a dynamic exchange of metal cations between the electrocatalyst and electrolyte. Understanding how iron in the electrolyte gets incorporated in the nickel hydroxide electrocatalyst is critical for pinpointing the roles of Fe during water oxidation. Here, we report that iron incorporation and oxygen evolution reaction (OER) are highly coupled, especially at high working potentials. The iron incorporation rate is much higher at OER potentials than that at the OER dormant state (low potentials). At OER potentials, iron incorporation favors electrochemically more reactive edge sites, as visualized by synchrotron X-ray fluorescence microscopy. Using X-ray absorption spectroscopy and density functional theory calculations, we show that Fe incorporation can suppress the oxidation of Ni and enhance the Ni reducibility, leading to improved OER catalytic activity. Our findings provide a holistic approach to understanding and tailoring Fe incorporation dynamics across the electrocatalyst-electrolyte interface, thus controlling catalytic processes.