Bimetal-bridging Nitrogen Coordination in Carbon-based Electrocatalysts for pH-universal Oxygen Reduction.

Electrocatalysts with atomically dispersed metal sites (e.g., metal-nitrogen-carbon) have been deemed as promising alternatives for noble-metal catalysts in couples of electrocatalytic reactions. However, the modulation of such atomic sites and the understanding of their interactions are still highly challenging. Herein, we propose a unique supermolecule assembly-profile coating strategy to prepare a series of diatomic electrocatalysts by profile coating of eight Prussian blue analogues (PBAs) on supramolecular supports respectively as bimetallic sources. The detailed microstructure analysis revealed that the metal-nitrogen-carbon sites with four- (Zn-N4 ) and five-coordination (Fe-N5 ) via the nitrogen coordination are similar to the cytochrome c oxidases. For promising electrocatalysis, such unique microstructure is able to activate oxygen molecules due to nitrogen-bonding coordination with bimetal sites, thus leading to efficient four-electron oxygen reduction in alkaline, neutral, and acid electrolytes. Especially, zinc group elements (e.g., Zn and Cd) with d10 electron configuration would significantly boost the nitrogen-bonding coordination with bimetal sites to enhance electrocatalytic activity. The proof-of-concept for the general synthesis of advanced electrocatalysts with controllable bimetal active sites and the mechanistic understanding will promote the promising electrocatalysis by applying the similar principles.

Thermal-Driven Dispersion of Bismuth Nanoparticles among Carbon Matrix for Efficient Carbon Dioxide Reduction.

The poor electrocatalytic stability and rapid deactivation of metal electrocatalysts are always present in the electrocatalytic conversion of carbon dioxide (CO2) due to the harsh reduction condition. Herein, we demonstrate the controllable dispersion of ultrafine bismuth nanoparticles among the hollow carbon shell (Bi@C-700-4) simply by a thermal-driven diffusion process. The confinement effect of nitrogen-doped carbon matrix is able to low the surface energy of bismuth nanoparticles against the easy aggregation commonly observed for the thermal treatment. On the basis of the synergistic effect and confinement effect between bismuth nanoparticles and carbon matrix, the highly dispersed active sites render the obviously improved electrocatalytic activity and stability for CO2 reduction into formate. The in situ experimental observations on the reduction process and theoretical calculations reveal that the incorporation of bismuth nanoparticles with nitrogen-doped carbon matrix would promote the activation of CO2 and the easy formation of key intermediate (*OCHO), thus leading the enhanced electrocatalytic activity, with a Faradaic Efficiency (FE) of formate about 94.8 % and the long-time stability. Furthermore, the coupling of an anode for 5-hydroxymethylfurfural oxidation reaction (HMFOR) in solar-driven system renders the high 2,5-furandicarboxylic acid (FDCA) yield of 81.2 %, presenting the impressive solar-to-fuel conversion.

Bionic Mineralization toward Scalable MOF Films for Ampere-Level Biomass Upgrading.

With significant advances in metal-organic framework (MOF) nanostructure preparation, however, the facile synthesis of large-scale MOF films with precise control of the interface structure and surface chemistry is still challenging to achieve with satisfactory performance. Herein, we introduce a universal strategy bridging metal corrosion chemistry and bionic mineralization to synthesize 16 MOF films on 7 metal supports under ambient conditions. The robustness to explore unlimited libraries of MOF films (e.g., carboxylate-, N-heterocycle-, phenolic-, and phosphonate-MOFs) on supports is evoked by independently regulating the metal redox behavior, electrolyte properties, and organic ligands along with hydrogen evolution or oxygen reduction, which offers the basic guidelines for regulating the microstructure and composition of MOFs on the Pourbaix diagram. In conjunction with multiple manufacturing methods, we demonstrated proof of concept for "printing" a large variety of MOF patterns from micrometer to meter scales. Furthermore, a large-area electrolyzer (64 cm2) devised enables 5-hydroxymethylfurfural oxidation to achieve a record-breaking current of 3.0 A at 1.63 V with 2,5-furandicarboxylic acid production, leading to the simultaneous production of H2 gas and valuable feedstocks. The improved electrocatalytic activity for significantly boosting the 5-hydroxymethylfurfural oxidation exemplifies one of the functional MOF films for given applications beyond biomass upgrading.

Interface Molecular Functionalization of Cu2O for Synchronous Electrocatalytic Generation of Formate.

The electrocatalytic generation of valuable fuels and chemicals from carbon dioxide (CO2) and others with the assistance of clean solar energy is a highly promising way to realize the carbon-neutral cycle, which invokes the systematic development of advanced electrocatalysts for efficient and selective redox reactions of feedstocks. Herein, we demonstrate the interface modification of cuprous oxide with polyvinylpyrrolidone (PVP) to improve the electrocatalytic efficiency for the synchronous formate generation. Density functional theory calculations reveal that the interfacial properties can be effectively regulated by the PVP functionalization for the favorable formation of intermediates to improve the selectivity of formate generation. Importantly, the advanced electrocatalyts enable an efficient coupling of CO2 reduction with methanol oxidation in an electrochemical cell powered with a solar cell. The work provides a predictive link between the electrocatalytic redox reactions by applying the interfacial regulation strategies of electrocatalysts.

Microsized Gray Tin as a High-Rate and Long-Life Anode Material for Advanced Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are developed to address the serious concern about the limited resources of lithium. To achieve high energy density, anode materials with a large specific capacity and a low operation voltage are highly desirable. Herein, microsized particles of gray Sn (α-Sn) are explored as an anode material of SIBs for the first time. The distinct structure of α-Sn endows it the reduced volume change, the improved interaction with polymer binders and the in situ formation of amorphous Sn, as supported by in situ XRD, TEM and DFT calculations. Therefore, α-Sn exhibits an excellent electrochemical performance, much better than ß-Sn widely used before. Even microsized particles of α-Sn without any treatments deliver a capacity of ∼451 mAh g-1 after 3500 cycles at 2 A g-1 or ∼464 mAh g-1 at 4 A g-1 in a rate test. The results indicate the promising potential of α-Sn in SIBs.

Physicochemical Confinement Effect Enables High-Performing Zinc-Iodine Batteries.

Zinc-iodine batteries are promising energy storage devices with the unique features of aqueous electrolytes and safer zinc. However, their performances are still limited by the polyiodide shuttle and the unclear redox mechanism of iodine species. Herein, a single iron atom was embedded in porous carbon with the atomic bridging structure of metal-nitrogen-carbon to not only enhance the confinement effect but also invoke the electrocatalytic redox conversion of iodine, thereby enabling the large capacity and good cycling stability of the zinc-iodine battery. In addition to the physical trapping effect of porous carbon with good electronic conductivity, the in situ experimental characterization and theoretical calculation reveal that the metal-nitrogen-carbon bridging structure modulates the electronic properties of carbon and adjusts the intrinsic activity for the reversible conversion of iodine via the thermodynamically favorable pathway. This work demonstrates that the physicochemical confinement effect can be invoked by the rational anchoring of a single metal atom with nitrogen in a porous carbon matrix to enhance the electrocatalytic redox conversion of iodine, which is crucial to fabricating high-performing zinc-iodine batteries and beyond by applying the fundamental principles.

Interface Coordination Stabilizing Reversible Redox of Zinc for High-Performance Zinc-Iodine Batteries.

Aqueous Zn batteries (AZBs) have attracted extensive attention due to good safety, cost-effectiveness, and environmental benignity. However, the sluggish kinetics of divalent zinc ion and the growth of Zn dendrites severely deteriorate the cycling stability and specific capacity. The authors demonstrate modulation of the interfacial redox process of zinc via the dynamic coordination chemistry of phytic acid with zinc ions. The experimental results and theoretical calculation reveal that the in-situ formation of such inorganic-organic films as a dynamic solid-electrolyte interlayer is efficient to buffer the zinc ion transfer via the energy favorable coordinated hopping mechanism for the reversible zinc redox reactions. Especially, along the interfacial coating layer with porous channel structure is able to regulate the solvation structure of zinc ions along the dynamic coordination of the phytic acid skeleton, efficiently inhibiting the surface corrosion of zinc and dendrite growth. Therefore, the resultant Zn anode achieves low voltage hysteresis and long cycle life at rigorous charge and discharge circulation for fabricating highly robust rechargeable batteries. Such an advanced strategy for modulating ion transport demonstrates a highly promising approach to addressing the basic challenges for zinc-based rechargeable batteries, which can potentially be extended to other aqueous batteries.

Atomic Bridging Structure of Nickel-Nitrogen-Carbon for Highly Efficient Electrocatalytic Reduction of CO2.

To meet strategic applications, electrochemical reduction of CO2 into value-added chemical molecules would be improved by the rational design of advanced electrocatalysts with atomically dispersed active sites. Herein an electrospun-pyrolysis cooperative strategy is presented to not only modulate the porous structure of the carbon support for favorable charge and mass transfer, but also adjust the bridging structure of atomically dispersed metal species. Typically, the experimental results and theoretical calculations revealed that the unique chemical structure of binuclear nickel bridging with nitrogen and carbon atoms (namely Ni2 -N4 -C2 ) tunes the electronic nature of the d-states for the optimal adsorption of carbon dioxide and intermediates, thus inducing the substantial enhancement of CO2 reduction via the thermodynamically more favorable pathway. The identification of such a structure demonstrates the large space to modulate the atomic bridging status for optimizing electrocatalysis.

Iodine Redox Chemistry in Rechargeable Batteries.

Halogens have been coupled with metal anodes in a single cell to develop novel rechargeable batteries based on extrinsic redox reactions. Since the commercial introduction of lithium-iodine batteries in 1972, they have shown great potential to match the high-rate performance, large energy density, and good safety of advanced batteries. With the development of metal anodes (e.g. Li, Zn), one of the actual challenges lies in the preparation of electrochemically active and reliable iodine-based cathodes to prevent self-discharge and capacity decay of the rechargeable batteries. Understanding the fundamental reactions of iodine/polyiodide and their underlying mechanisms is still highly desirable to promote the rational design of advanced cathodes for high-performance rechargeable batteries. In this Minireview, recent advances in the development of iodine-based cathodes to fabricate rechargeable batteries are summarized, with a special focus on the basic principles of iodine redox chemistry to correlate with structure-function relationships.

Cation Intercalation in Manganese Oxide Nanosheets: Effects on Lithium and Sodium Storage.

The rapid development of advanced energy-storage devices requires significant improvements of the electrode performance and a detailed understanding of the fundamental energy-storage processes. In this work, the self-assembly of two-dimensional manganese oxide nanosheets with various metal cations is introduced as a general and effective method for the incorporation of different guest cations and the formation of sandwich structures with tunable interlayer distances, leading to the formation of 3D Mx MnO2 (M=Li, Na, K, Co, and Mg) cathodes. For sodium and lithium storage, these electrode materials exhibited different capacities and cycling stabilities. The efficiency of the storage process is influenced not only by the interlayer spacing but also by the interaction between the host cations and shutter ions, confirming the crucial role of the cations. These results provide promising ideas for the rational design of advanced electrodes for Li and Na storage.

Strong p-d Orbital Hybridization on Bismuth Nanosheets for High Performing CO2 Electroreduction.

Single-atom alloys (SAAs) show great potential for a variety of electrocatalytic reactions. However, the atomic orbital hybridization effect of SAAs on the electrochemical reactions is unclear yet. Herein, the in situ confinement of vanadium/molybdenum/tungsten atoms on bismuth nanosheet is shown to create SAAs with rich grain boundaries, respectively. With the detailed analysis of microstructure and composition, the strong p-d orbital hybridization between bismuth and vanadium enables the exceptional electrocatalytic performance for carbon dioxide (CO2 ) reduction with the Faradaic efficiency nearly 100% for C1 products in a wide potential range from -0.6 to -1.4 V, and a long-term electrolysis stability for 90 h. In-depth in situ investigations with theoretical computations reveal that the electron delocalization toward vanadium atoms via the p-d orbital hybridization evokes the bismuth active centers for efficient CO2 activation via the σ-donation of O-to-Bi, thus reduces protonation energy barriers for formate production. With such fundamental understanding, SAA electrocatalyst is employed to fabricated the solar-driven electrolytic cell of CO2 reduction and 5-hydroxymethylfurfural oxidation, achieving an outstanding 2,5-furandicarboxylic acid yield of 90.5%. This study demonstrates a feasible strategy to rationally design advanced SAA electrocatalysts via the basic principles of p-d orbital hybridization.

Coordination modulation of hydrated zinc ions to enhance redox reversibility of zinc batteries.

The dendrite growth of zinc and the side reactions including hydrogen evolution often degrade performances of zinc-based batteries. These issues are closely related to the desolvation process of hydrated zinc ions. Here we show that the efficient regulation on the solvation structure and chemical properties of hydrated zinc ions can be achieved by adjusting the coordination micro-environment with zinc phenolsulfonate and tetrabutylammonium 4-toluenesulfonate as a family of electrolytes. The theoretical understanding and in-situ spectroscopy analysis revealed that the favorable coordination of conjugated anions involved in hydrogn bond network minimizes the activate water molecules of hydrated zinc ion, thus improving the zinc/electrolyte interface stability to suppress the dendrite growth and side reactions. With the reversibly cycling of zinc electrode over 2000 h with a low overpotential of 17.7 mV, the full battery with polyaniline cathode demonstrated the impressive cycling stability for 10000 cycles. This work provides inspiring fundamental principles to design advanced electrolytes under the dual contributions of solvation modulation and interface regulation for high-performing zinc-based batteries and others.

Atomic bismuth induced ensemble sites with indium towards highly efficient and stable electrocatalytic reduction of carbon dioxide.

Structural reconstruction is commonly observed during electrocatalytic CO2 reduction (CO2RR) process. However, the proper modulation of interface and defect sites remains challenging with the mechanism understanding to realize the favorable electrocatalysis. Herein, the atomic bridging of bismuth with indium atoms is elaborately designed for improving electrocatalysis of CO2RR via electrochemical reduction and in situ anchoring strategy. As revealed by in situ structure analysis and theoretical studies, the ensemble sites supported on carbon matrix enable the charge density gradient to significantly promote the adsorption of *OCHO intermediate by the regulation of σ bonding and π* back-donation. Consequently, such unique electrocatalyst achieves the high formate faradaic efficiency of 95.1% over the entire potential range tested and the long-lived stability for 9 d. With coupling of CO2RR, the solar-driven full cell demonstrates the spontaneous production of formate and 2,5-furandicarboxylic acid via the efficient oxidation of 5-hydroxymethylfurfural with an outstanding yield of 88.2%, highlighting the impressive solar-to-fuel conversion selectivity. Monitoring and understanding the intrinsic active sites of biatomic bridge are crucial to elucidate the synergic electrocatalysis for rationally designing high-performance electrocatalysts.

Preparation of Hierarchical Cube-on-plate Metal Phosphides as Bifunctional Electrocatalysts for Overall Water Splitting.

To rationally design efficient and cost-effective electrocatalysts, a simple but efficient strategy has been developed to directly anchor prussian blue analogue (PBA) nanocubes on cobalt hydroxide nanoplates (PBA@Co(OH)2 ) via the in-situ interfacial precipitation process. Subsequently, the thermal treatment in the presence of sodium hydrogen phosphite enabled the successful transition into metal phosphides with the hierarchical cube-on-plate structure. When used as electrocatalytsts, the obtained bimetal phosphides exhibited good bifunctional electrocatalytic activities for hydrogen and oxygen evolution reactions with good long-term stability. Thus, an enhanced performance for overall water splitting can be achieved, which could be ascribed to the hierarchical structure and favorable composition of as-prepared bimetal phosphide for rapid electron and mass transfer. The present study demonstrates a favorable approach to modulate the composition and structure of metal phosphide for enhancing the electrocatalytic ability toward water splitting.

A 3D and Stable Lithium Anode for High-Performance Lithium-Iodine Batteries.

Lithium metal is considered as the most promising anode material due to its high theoretical specific capacity and the low electrochemical reduction potential. However, severe dendrite problems have to be addressed for fabricating stable and rechargeable batteries (e.g., lithium-iodine batteries). To fabricate a high-performance lithium-iodine (Li-I2 ) battery, a 3D stable lithium metal anode is prepared by loading of molten lithium on carbon cloth doped with nitrogen and phosphorous. Experimental observations and theoretical calculation reveal that the N,P codoping greatly improves the lithiophilicity of the carbon cloth, which not only enables the uniform loading of molten lithium but also facilitates reversible lithium stripping and plating. Dendrites formation can thus be significantly suppressed at a 3D lithium electrode, leading to stable voltage profiles over 600 h at a current density of 3 mA cm-2 . A fuel cell with such an electrode and a lithium-iodine cathode shows impressive long-term stability with a capacity retention of around 100% over 4000 cycles and enhanced high-rate capability. These results demonstrate the promising applications of 3D stable lithium metal anodes in next-generation rechargeable batteries.

A rechargeable iodine-carbon battery that exploits ion intercalation and iodine redox chemistry.

Graphitic carbons have been used as conductive supports for developing rechargeable batteries. However, the classic ion intercalation in graphitic carbon has yet to be coupled with extrinsic redox reactions to develop rechargeable batteries. Herein, we demonstrate the preparation of a free-standing, flexible nitrogen and phosphorus co-doped hierarchically porous graphitic carbon for iodine loading by pyrolysis of polyaniline coated cellulose wiper. We find that heteroatoms could provide additional defect sites for encapsulating iodine while the porous carbon skeleton facilitates redox reactions of iodine and ion intercalation. The combination of ion intercalation with redox reactions of iodine allows for developing rechargeable iodine-carbon batteries free from the unsafe lithium/sodium metals, and hence eliminates the long-standing safety issue. The unique architecture of the hierarchically porous graphitic carbon with heteroatom doping not only provides suitable spaces for both iodine encapsulation and cation intercalation but also generates efficient electronic and ionic transport pathways, thus leading to enhanced performance.Carbon-based electrodes able to intercalate Li+ and Na+ ions have been exploited for high performing energy storage devices. Here, the authors combine the ion intercalation properties of porous graphitic carbons with the redox chemistry of iodine to produce iodine-carbon batteries with high reversible capacities.

Silver-modified mesoporous TiO2 photocatalyst for water purification.

Mesoporous anatase (TiO(2)) was modified with silver (Ag) nanoparticles using a photoreduction method. Performance of the resulting TiO(2)-Ag nanocomposites for water purification was evaluated using degradation of Rhodamine B (RhB) and disinfection of Escherichia coli (E. coli) under ultraviolet (UV) irradiation. The composites with different Ag loadings were characterized using physical adsorption of nitrogen, X-ray diffraction, X-ray photoelectron spectroscopy and UV-Visible diffuse reflectance spectroscopic techniques. The results showed that metallic Ag nanoparticles were firmly immobilized on the TiO(2) surface, which improved electron-hole separation by forming the Schottky barrier at the TiO(2)-Ag interface. Photocatalytic degradation of RhB and inactivation of E. coli effectively occurred in an analogical trend. The deposited Ag slightly decreased adsorption of target pollutants, but greatly increased adsorption of molecular oxygen with the latter enhancing production of reactive oxygen species (ROSs) with concomitant increase in contaminant photodegradation. The optimal Ag loadings for RhB degradation and E. coli disinfection were 0.25 wt% and 2.0 wt%, respectively. The composite photocatalysts were stable and could be used repeatedly under UV irradiation.

Photocatalytic degradation of dyes over graphene-gold nanocomposites under visible light irradiation.

Graphene modified with gold nanoparticles displayed an excellent visible-light photocatalytic performance in degrading dyes in water.