Herein, recent progress in the field of tin oxide (SnO2)‐based nanosized and nanostructured materials as conversion and alloying/dealloying‐type anodes in lithium‐ion batteries and beyond (sodium‐ ...and potassium‐ion batteries) is briefly discussed. The first section addresses the importance of the initial SnO2 micro‐ and nanostructure on the conversion and alloying/dealloying reaction upon lithiation and its impact on the microstructure and cyclability of the anodes. A further section is dedicated to recent advances in the fabrication of diverse 0D to 3D nanostructures to overcome stability issues induced by large volume changes during cycling. Additionally, the role of doping on conductivity and synergistic effects of redox‐active and ‐inactive dopants on the reversible lithium‐storage capacity and rate capability are discussed. Furthermore, the synthesis and electrochemical properties of nanostructured SnO2/C composites are reviewed. The broad research spectrum of SnO2 anode materials is finally reflected in a brief overview of recent work published on Na‐ and K‐ion batteries.
A matter of size and structure: Large volume changes during SnO2 conversion and alloying of an anode limit its stability upon cycling. A brief overview of how primary particle size, nanostructuring, and composite formation influence the electrode performance and stability in SnO2 anode‐based lithium‐ion batteries is provided and complemented by recent reports on corresponding sodium and potassium systems.
A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water ...oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open‐porous morphology are synthesized that reach a conductivity of ≈3.6 S cm−1 and are further used as catalyst support. ATO‐supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrOx colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO‐supported IrO2 nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm−3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A gIr−1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO2‐supported IrO2 reference catalyst under the same measurement conditions.
Illustration of the solvothermal loading of open porous antimony doped tin oxide microparticles employed as a catalyst support with a thin layer of catalytic highly active IrO2 nanoparticles is shown. Independent control of the microparticle porosity, doping level, as well as of the IrOx precursor‐to‐support ratio allows for the synthesis of an optimized supported oxygen evolution reaction (OER) catalyst with high catalytic activity for the OER.
Oxygen evolution reaction (OER) is expected to be of great importance for the future energy conversion and storage in form of hydrogen by water electrolysis. Besides the traditional noble‐metal or ...transition metal oxide‐based catalysts, carbonaceous electrocatalysts are of great interest due to their huge structural and compositional variety and unrestricted abundance. This review provides a summary of recent advances in the field of carbon‐based OER catalysts ranging from “pure” or unintentionally doped carbon allotropes over heteroatom‐doped carbonaceous materials and carbon/transition metal compounds to metal oxide composites where the role of carbon is mainly assigned to be a conductive support. Furthermore, the review discusses the recent developments in the field of ordered carbon framework structures (metal organic framework and covalent organic framework structures) that potentially allow a rational design of heteroatom‐doped 3D porous structures with defined composition and spatial arrangement of doping atoms to deepen the understanding on the OER mechanism on carbonaceous structures in the future. Besides introducing the structural and compositional origin of electrochemical activity, the review discusses the mechanism of the catalytic activity of carbonaceous materials, their stability under OER conditions, and potential synergistic effects in combination with metal (or metal oxide) co‐catalysts.
Advanced carbonaceous oxygen evolution reaction catalysts for water‐splitting applications rely on synthesis procedures enabling formation of nanosized 3D, defect‐rich, and heteroatom‐doped carbon structures and inorganic particle‐containing hybrid materials. Parameters affecting the electrocatalytic activity include defect engineering, heteroatom doping, and hybrid composite formation as well as the formation of framework structures defined by molecular building blocks.
Potassium‐ion batteries (PIBs) have favorable characteristics in terms of cell voltage and cost efficiency, making them a promising technology for grid‐scale energy storage. The rational design of ...suitable electrode materials on a theoretical basis, aiming at high power and energy density, is of paramount importance to bring this battery technology to the practical market. In this paper, a series of iron‐based compounds with different non‐metal anions are selectively synthesized to investigate the nature of kinetic differences induced by anionic modulation. A combination of experimental characterization and theoretical calculation reveals that iron phosphide, with its moderate adsorption energy (Ea) and lowest diffusion barrier (Eb), exhibits the best cycling and rate properties at low electrochemical polarization, which is related to the narrow Δd‐p band center gap that facilitates ion transfer. In addition, the optimization of the electrolyte formula results in the carbon‐supported iron phosphide anode running stably over 2000 cycles at 0.5 A g−1 and exhibiting a high rate capacity of 81.1 mAh g−1 at 2 A g−1. The superior electrochemical properties are attributed to the robust KF‐rich solid electrolyte interphase formed by the highly compatible KFSI in ethylene carbonate (EC)/diethyl carbonate (DEC) configuration.
Equilibrium “Ea‐Eb” relationship, i.e., the moderate adsorption energy and lowest diffusion barrier originated from narrow Δp‐d bandgap, as well as compatible electrolyte formula, is found to facilitate the most effective ionic transfer from the surface to the bulk of electrode with guaranteed capacity and redox kinetics.
The beneficial effects of Sn(IV) as a dopant in ultrathin hematite (α‐Fe2O3) photoanodes for water oxidation are examined. Different Sn concentration profiles are prepared by alternating atomic layer ...deposition of Fe2O3 and SnO
x
. Combined data from spectrophotometry and intensity‐modulated photocurrent spectroscopy yields the individual process efficiencies for light harvesting, charge separation, and charge transfer. The best performing photoanodes are Sn‐doped both on the surface and in the subsurface region and benefit from enhanced charge separation and transfer. Sn‐doping throughout the bulk of the hematite photoanode causes segregation at the grain boundaries and hence a lower overall efficiency. Fe2O3 (0001) and terminations, shown to be dominant by microstructural analysis, are investigated by density functional theory (DFT) calculations. The energetics of surface intermediates during the oxygen evolution reaction (OER) reveal that while Sn‐doping decreases the overpotential on the (0001) surface, the Fe2O3 orientation shows one of the lowest overpotentials reported for hematite so far. Electronic structure calculations demonstrate that Sn‐doping on the surface also enhances the charge transfer efficiency by elimination of surface hole trap states (passivation) and that subsurface Sn‐doping introduces a gradient of the band edges that reinforces the band bending at the semiconductor/electrolyte interface and thus boosts charge separation.
Ultrathin hematite films with surface and subsurface tin‐doping show greatly enhanced charge separation and charge transfer in photoelectrochemical water oxidation.
Solid‐state sodium batteries (SSNBs) have attracted extensive interest due to their high safety on the cell level, abundant material resources, and low cost. One of the major challenges in the ...development of SSNBs is the suppression of sodium dendrites during electrochemical cycling. The solid electrolyte Na3.4Zr2Si2.4P0.6O12 (NZSP) exhibits one of the best dendrite tolerances of all reported solid electrolytes (SEs), while it also shows interesting dendrite growth along the surface of NZSP rather than through the ceramic. Operando investigations and in situ scanning electron microscopy microelectrode experiments are conducted to reveal the Na plating mechanism. By blocking the surface from atmosphere access with a sodium‐salt coating, surface‐dendrite formation is prevented. The dendrite tolerance of Na | NZSP | Na symmetric cells is then increased to a critical current density (CCD) of 14 mA cm−2 and galvanostatic cycling of 1 mA cm−2 and 1 mAh cm−2 (half cycle) is demonstrated for more than 1000 h. Even if the current density is increased to 3 mA cm−2 or 5 mA cm−2, symmetric cells can still be operated for 180 h or 12 h, respectively.
Fast Na‐dendrite growth along the surface of Na3.4Zr2Si2.4P0.6O12 (NZSP) rather than through the ceramic is observed. Atmosphere and surface‐coating influence the surface‐dendrite growth on NZSP. After coating the NZSP surface with a protective layer, the critical current density of the Na | NZSP | Na symmetric cells increases up to 14 mA cm−2. The cell withstands galvanostatic cycling with 1 mA cm−2 and 1 mAh cm−2 for 1000 h.
Fattakhova-Rohlfing et al examine three-dimensional titanium dioxide (TiO2) nanomaterials. They focus on porous films, porous spheres, hierarchical hollow spheres, porous fibers, and ...three-dimensional titania materials with hierarchical morphology.
The n‐type semiconducting spinel zinc ferrite (ZnFe2O4) is used as a photoabsorber material for light‐driven water‐splitting. It is prepared for the first time by atomic layer deposition. Using the ...resulting well‐defined thin films as a model system, the performance of ZnFe2O4 in photoelectrochemical water oxidation is characterized. Compared to benchmark α‐Fe2O3 (hematite) films, ZnFe2O4 thin films achieve a lower photocurrent at the reversible potential. However, the oxidation onset potential of ZnFe2O4 is 200 mV more cathodic, allowing the water‐splitting reaction to proceed at a lower external bias and resulting in a maximum applied‐bias power efficiency (ABPE) similar to that of Fe2O3. The kinetics of the water oxidation reaction are examined by intensity‐modulated photocurrent spectroscopy. The data indicate a considerably higher charge transfer efficiency of ZnFe2O4 at potentials between 0.8 and 1.3 V versus the reversible hydrogen electrode, attributable to significantly slower surface charge recombination. Finally, nanostructured ZnFe2O4 photoanodes employing a macroporous antimony‐doped tin oxide current collector reach a five times higher photocurrent than the flat films. The maximum ABPE of these host–guest photoanodes is similarly increased.
Zinc ferrite thin films prepared by atomic layer deposition exhibit slow surface electron/hole recombination during photoelectrochemical water oxidation. Nanostructuring can be used to significantly increase their photocurrent.
This review discusses the contribution of physical vapor deposition (PVD) processes to the development of electrochemical energy storage systems with emphasis on solid‐state batteries. A brief ...overview of different PVD technologies and details highlighting the utility of PVD for the fabrication and characterization of individual battery materials are provided. In this context, the key methods that have been developed for the fabrication of solid electrolytes and active electrode materials with well‐defined properties are described, and demonstrations of how these techniques facilitate the in‐depth understanding of fundamental material properties and interfacial phenomena as well as the development of new materials are provided. Beyond the discussion of single components and interfaces, the progress on the device scale is also presented. State‐of‐the‐art solid‐state batteries, both academic and commercial types, are assessed in view of energy and power density as well as long‐term stability. Finally, recent efforts to improve the power and energy density through the development of 3D‐structured cells and the investigation of bulk cells are discussed.
The review discusses how the development of electrochemical energy storage systems and particularly solid‐state batteries can benefit from physical vapor deposition processes, from the basic understanding of the structure and properties of individual materials and their interfaces to the processing and fabrication of complete batteries.
In recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next‐generation batteries. In this ...respect, Na3.4Zr2Si2.4P0.6O12 is a promising solid electrolyte for solid‐state sodium batteries, due to its high ionic conductivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time‐resolved impedance analysis, in situ X‐ray photoelectron spectroscopy, and transmission electron microscopy. Based on pressure‐ and temperature‐dependent impedance analyses, it is concluded that the Na|Na3.4Zr2Si2.4P0.6O12 interface kinetics is dominated by current constriction rather than by charge transfer. Cross‐sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time‐resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibration is faster and mainly caused by creep at increased external load. The presented information provides useful insights into a more profound evaluation of the sodium metal anode in solid‐state batteries.
The interfacial stability and the dissolution kinetics under external current load of a Na3.4Zr2Si2.4P0.6O12 solid electrolyte in contact with sodium metal are systematically studied. Beside the formation of a kinetically stabilized interphase, current constriction is identified as a dominating process at the interface. After anodic dissolution a pronounced equilibration of the formed interfacial morphology is observed at resting conditions.
PDF
