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Abstract Cobalt oxyhydroxide (CoOOH) is a promising catalytic material for oxygen evolution reaction (OER). In the traditional CoOOH structure, Co3+ exhibits a low-spin state configuration ( $${t}_{2{{{{{\rm{g}}}}}}}^{6}{e}_{{{{{{\rm{g}}}}}}}^{0}$$ t 2 g 6 e g 0 ), with electron transfer occurring in face-to-face $${t}_{2{{{{{\rm{g}}}}}}}^{*}$$ t 2 g * orbitals. In this work, we report the successful synthesis of high-spin state Co3+ CoOOH structure, by introducing coordinatively unsaturated Co atoms. As compared to the low-spin state CoOOH, electron transfer in the high-spin state CoOOH occurs in apex-to-apex $${e}_{{{{{{\rm{g}}}}}}}^{*}$$ e g * orbitals, which exhibits faster electron transfer ability. As a result, the high-spin state CoOOH performs superior OER activity with an overpotential of 226 mV at 10 mA cm−2, which is 148 mV lower than that of the low-spin state CoOOH. This work emphasizes the effect of the spin state of Co3+ on OER activity of CoOOH based electrocatalysts for water splitting, and thus provides a new strategy for designing highly efficient electrocatalysts.

Abstract A coupled oxygen evolution mechanism (COM) during oxygen evolution reaction (OER) has been reported in nickel oxyhydroxides (NiOOH)-based materials by realizing e g * band (3d electron states with e g symmetry) broadening and light irradiation. However, the link between the e g * band broadening extent and COM-based OER activities remains unclear. Here, Ni1-xFexOOH (x = 0, 0.05, 0,2) are prepared to investigate the underlying mechanism governing COM-based activities. It is revealed that in low potential region, realizing stronger e g * band broadening could facilitate the *OH deprotonation. Meanwhile, in high potential region where the photon utilization is the rate-determining step, a stronger e g * band broadening would widen the non-overlapping region between d z 2 and a 1g * orbitals, thereby enhancing photon utilization efficiency. Consequently, a stronger e g * band broadening could effectuate more efficient OER activities. Moreover, we demonstrate the universality of this concept by extending it to reconstruction-derived X-NiOOH (X = NiS2, NiSe2, Ni4P5) with varying extent of e g * band broadening. Such an understanding of the COM would provide valuable guidance for the future development of highly efficient OER electrocatalysts.

Summary: Despite their widespread study, lithium metal anodes still face the bottleneck problem of low average Coulombic efficiency. Herein, we adopt an electroless plating method and introduce additive (vanillin) to develop nanoscale silver hosts. The uniform nanoscale silver layer is conducive to seamless Li/Ag alloying process, thereby enabling flat lithium deposition. Since the Li/Ag alloying process occurs after the formation of solid electrolyte interphase (SEI), the seamless alloying process stabilizes the SEI, which improves the reversibility of the lithium metal anode. On this basis, a 3D-printed copper host-coated dense nanoscale silver layer is constructed, which reduces the effective current density and hence lowers the polarization of lithium deposition or stripping. Moreover, the 3D structure induces the epitaxial growth of lithium and thus alleviates the volume change of lithium metal. As a result, an average Coulombic efficiency of 99.61% is achieved in the Li/3D Ag half-cell.

Cobalt oxyhydroxide (CoOOH) is a promising catalytic material for oxygen evolution reaction (OER). In the traditional CoOOH structure, Co3+ exhibits a low-spin state configuration ( t 2 g 6 e g 0 ), with electron transfer occurring in face-to-face t 2 g * orbitals. In this work, we report the successful synthesis of high-spin state Co3+ CoOOH structure, by introducing coordinatively unsaturated Co atoms. As compared to the low-spin state CoOOH, electron transfer in the high-spin state CoOOH occurs in apex-to-apex e g * orbitals, which exhibits faster electron transfer ability. As a result, the high-spin state CoOOH performs superior OER activity with an overpotential of 226 mV at 10 mA cm−2, which is 148 mV lower than that of the low-spin state CoOOH. This work emphasizes the effect of the spin state of Co3+ on OER activity of CoOOH based electrocatalysts for water splitting, and thus provides a new strategy for designing highly efficient electrocatalysts. Regulating spin state of metal cations in catalysts is recognized as a strategy to improve water oxidation. Herein, the authors constructed high-spin cobalt ions in cobalt oxyhydroxides, experimentally demonstrating accelerated electron transfer ability and thereby superior water oxidation performance. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting to generate hydrogen energy fills a gap in the intermittency issues for wind and sunlight power. Transition metal (TM) oxides have attracted significant interest in water oxidation due to their availability and excellent activity. Typically, the transitional metal oxyhydroxides species derived from these metal oxides are often acknowledged as the real catalytic species, due to the irreversible structural reconstruction. Hence, in order to innovatively design new catalyst, it is necessary to provide a comprehensive understanding for the origin of surface reconstruction. In this review, the most recent developments in the reconstruction of transition metal‐based oxygen evolution reaction electrocatalysts were introduced, and various chemical driving forces behind the reconstruction mechanism were discussed. At the same time, specific strategies for modulating pre‐catalysts to achieve controllable reconfiguration, such as metal substituting, increase of structural defect sites, were summarized. At last, the issues for the further understanding and optimization of transition metal oxides compositions based on structural reconstruction were provided. [ABSTRACT FROM AUTHOR]

Recently, due to its flexibility and ease of integration into wearable electronics, interest in fiber‐shaped batteries (FSBs) is burgeoning. While there is much research focused on improving the electrochemical performance of FSBs, little work is done to evaluate the safety and comfort of integrated FSBs for wearable electronics, which will significantly hinder the further development of high‐performance FSBs and their commercialization. In this review, the design, integration, and evaluation of FSBs incorporated in common textiles are fully discussed. Traditional textile characterization techniques and modern methods to evaluate its durability are also summarized. Finally, in view of developing commercial wearable battery textiles, a perspective toward improving the design of high‐performance FSB is presented. [ABSTRACT FROM AUTHOR]

A coupled oxygen evolution mechanism (COM) during oxygen evolution reaction (OER) has been reported in nickel oxyhydroxides (NiOOH)-based materials by realizing eg* band (3d electron states with eg symmetry) broadening and light irradiation. However, the link between the eg* band broadening extent and COM-based OER activities remains unclear. Here, Ni1-xFexOOH (x = 0, 0.05, 0,2) are prepared to investigate the underlying mechanism governing COM-based activities. It is revealed that in low potential region, realizing stronger eg* band broadening could facilitate the *OH deprotonation. Meanwhile, in high potential region where the photon utilization is the rate-determining step, a stronger eg* band broadening would widen the non-overlapping region between dz2 and a1g* orbitals, thereby enhancing photon utilization efficiency. Consequently, a stronger eg* band broadening could effectuate more efficient OER activities. Moreover, we demonstrate the universality of this concept by extending it to reconstruction-derived X-NiOOH (X = NiS2, NiSe2, Ni4P5) with varying extent of eg* band broadening. Such an understanding of the COM would provide valuable guidance for the future development of highly efficient OER electrocatalysts. Coupled oxygen evolution mechanism provides an optimized electron transfer route during oxygen evolution process, but the underlying structure-activity relationship is still unclear. Here the authors investigate the role of eg* band broadening on the coupled oxygen evolution mechanism-based activities for Fe-doped NiOOH materials. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of surface reconstruction was critical to developing high performance lattice oxygen oxidation mechanism (LOM) based perovskite electrocatalysts. Traditionally, the primary determining factor of the surface reconstruction process was believed to be the oxygen vacancy formation energy. Hence, most previous studies focused on optimizing composition to reduce the oxygen vacancy formation energy, which in turn facilitated the surface reconstruction process. Here, for the first time, we found that adding oxyanions (SO42−, CO32−, NO3−) into the electrolyte could effectively regulate the solid–liquid interface, significantly accelerating the surface reconstruction process and enhancing oxygen evolution reaction (OER) activities. Further studies indicated that the added oxyanions would adsorb onto the solid–liquid interface layer, disrupting the dynamic equilibrium between the adsorbed OH− ions and the OH− ions generated during surface reconstruction process. As such, the OH− ions generated during surface reconstruction process could be more readily released into the electrolyte, thereby leading to an acceleration of the surface reconstruction. Thus, it was expected that our finding would provide a new layer of understanding to the surface reconstruction process in LOM‐based perovskite electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of high‐performance electrode materials is crucial for the advancement of sodium ion batteries (SIBs), and NiCo2S4 has been identified as a promising anode material due to its high theoretical capacity and abundant redox centers. However, its practical application in SIBs is hampered by issues such as severe volume variations and poor cycle stability. Herein, the Mn‐doped NiCo2S4@graphene nanosheets (GNs) composite electrodes with hollow nanocages were designed using a structure engineering method to relieve the volume expansion and improve the transport kinetics and conductivity of the NiCo2S4 electrode during cycling. Physical characterization and electrochemical tests, combined with density functional theory (DFT) calculations indicate that the resulting 3 % Mn‐NCS@GNs electrode demonstrates excellent electrochemical performance (352.9 mAh g−1 at 200 mA g−1 after 200 cycles, and 315.3 mAh g−1 at 5000 mA g−1). This work provides a promising strategy for enhancing the sodium storage performance of metal sulfide electrodes. [ABSTRACT FROM AUTHOR]

Transition metal‐based oxyhydroxides (MOOH) derived from the irreversible structural reconstruction of precatalysts are often acknowledged as the real catalytic species for the oxygen evolution reaction (OER). Typically, the reconstruction‐derived MOOH would exhibit superior OER activity compared to their directly synthesized counterparts, despite being fundamentally similar in chemistry. As such, structural reconstruction has emerged as a promising strategy to boost the catalytic activity of electrocatalysts. However, the in‐depth understanding of the origin of the superior OER activity of reconstructed materials still remains ambiguous, which significantly hinders the further developments of highly efficient electrocatalysts based on structural reconstruction chemistry. In this review, a comprehensive overview of the structural reconstruction behaviors in the reported reconstruction‐derived electrocatalysts is provided and the intrinsic chemical and structural origins of their high efficiency toward OER are unveiled. The fundamentals of structural reconstruction mechanisms, along with the recommended characterization techniques for the understanding of the dynamic structural reconstruction process and analyzing the structure of real catalytic species are also interpreted. Finally, in view of structural reconstruction chemistry, the potential perspectives to facilitate the design and synthesis of highly efficient and durable OER electrocatalyst are presented. [ABSTRACT FROM AUTHOR]

A fundamental understanding of surface reconstruction process is pivotal to developing highly efficient lattice oxygen oxidation mechanism (LOM) based electrocatalysts. Traditionally, the surface reconstruction in LOM based metal oxides is believed as an irreversible oxygen redox behavior, due to the much slower rate of OH− refilling than that of oxygen vacancy formation. Here, we found that the surface reconstruction in LOM based metal oxides is a spontaneous chemical reaction process, instead of an electrochemical reaction process. During the chemical process, the lattice oxygen atoms were attacked by adsorbed water molecules, leading to the formation of hydroxide ions (OH−). Subsequently, the metal‐site soluble atoms leached from the oxygen‐deficient surface. This work also suggests that the enhancement of surface hydrophilicity could accelerate the surface reconstruction process. Hence, such a finding could add a new layer for the understanding of surface reconstruction mechanism. [ABSTRACT FROM AUTHOR]

The development of inexpensive, active, and robust nonprecious metal electrocatalysts toward the oxygen evolution reaction (OER) in acid media is highly imperative for renewable energy conversion techniques, yet greatly challenging. Inspired by the vanadium‐containing oxygen‐fixing enzymes in haloperoxidase in nature, herein, the atomically dispersed V sites anchored on N‐doped multichannel carbon nanofibers (designated as V@NMCNFs hereafter) are rationally designed as high‐efficiency electrocatalyst for the acidic OER. Substantial characterizations validate that the local coordination microenvironment of the V site is identified as an asymmetrical penta‐coordinated V‐O2N3 moiety with axial VO coordination, which is further theoretically substantiated as an energetically favorable configuration with a reduced OER energy barrier by the density functional theory calculations. Consequently, the well‐dispersed isolated V‐O2N3 sites with exceptional intrinsic activity and unique nano‐architecture furnish the well‐designed V@NMCNFs with distinguished OER performance in a 0.5 m H2SO4 electrolyte, as reflected by the ultralow overpotential of 196 mV at 10 mA cm−2 and remarkable long‐term electrochemical durability, representing one of the most impressive nonprecious OER electrocatalysts to date. The synthetic methodology for SAC preparation and concept of electronic regulation proposed in this work offer perspectives to aid the design of other functional SAC systems with regulated coordination environments for efficient electrocatalysis. [ABSTRACT FROM AUTHOR]

A series of (1 − x)(K0.48Na0.52)NbO3‐x(Bi0.5Na0.5)(Zr0.55Ni0.45)O3‐δ (KNN‐BNZN) ceramics are designed to achieve excellent piezoelectric response along with narrow bandgap. The ceramics with x = 0.04 exhibit unprecedented piezoelectric coefficient d33 ~ 318±10pC N−1 in comparison with all reported narrow bandgap ceramics. A rhombohedral‐orthorhombic‐tetragonal (R‐O‐T) phase boundary is observed, indicating the formation of defect dipoles (Ni2+‐Vo¨) at morphotropic phase boundary region is desirable for piezo‐/ferroelectric properties. In addition, a narrow bandgap ~2.5 eV along with gap states (~0.9 eV and ~1.6 eV) is obtained from the ceramics when x > 0.02, which can be persuasively explained by the schematic plot of bandgap splitting mechanism proposed in this work, where Ni 3d energy state plays a role as a scaffold in the process of electron transition. More importantly, largely enhanced photovoltaic performance of the ceramics is achieved under AM 1.5 irradiation. The NIR photoresponse property (maximum current density of ~100 nA cm−2) indicates such KNN‐based ceramics with sub bandgap ~ 0.9 eV may even have potential to be applied in NIR light‐activated devices. Our findings might pave way for the further development of piezoelectric/photoresponsive multifunctional devices. [ABSTRACT FROM AUTHOR]