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Applications of room‐temperature–sodium sulfur (RT‐Na/S) batteries are currently impeded by the insulating nature of sulfur, the slow redox kinetics of sulfur with sodium, and the dissolution and migration of sodium polysulfides. Herein, a novel micrometer‐sized hierarchical S cathode supported by FeS2 electrocatalyst, which is grown in situ in well‐confined carbon nanocage assemblies, is presented. The hierarchical carbon matrix can provide multiple physical entrapment to polysulfides, and the FeS2 nanograins exhibit a low Na‐ion diffusion barrier, strong binding energy, and high affinity for sodium polysulfides. Their combination makes it an ideal sulfur host to immobilize the polysulfides and achieve reversible conversion of polysulfides toward Na2S. Importantly, the hierarchical S cathode is suitable for large‐scale production via the inexpensive and green spray‐drying method. The porous hierarchical S cathode offers a high sulfur content of 65.5 wt%, and can deliver high reversible capacity (524 mAh g−1 over 300 cycles at 0.1 A g−1) and outstanding rate capability (395 mAh g−1 at 1 A g−1 for 850 cycles), holding great promise for both scientific research and real application.

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Photoelectrochemical overall water splitting has been considered as a promising approach for producing chemical energy from solar energy. Although many photoelectrochemical cells have been developed for overall water splitting by coupling two semiconductor photoelectrodes, inefficient charge transfer between the light-harvesters and electron acceptor/donor severely restricts the solar energy conversion efficiency. Inspired by natural photosynthesis, we assembled a photoelectrochemical platform with multimediator modulation to achieve unassisted overall water splitting. Photogenerated electrons are transferred in order through multimediators driven by the electrochemical potential gradient, resulting in efficient charge separation and transportation with enhanced charge transfer rate and reduced charge recombination rate. The integrated system composed of inorganic oxide-based photoanode (BiVO4) and organic polymer-based photocathode (PBDB-T:ITIC:PC71BM) with complementary light absorption, exhibits a solar-to-hydrogen conversion efficiency as high as 4.3%. This work makes a rational design possible by constructing an efficient charge-transfer chain in artificial photosynthesis systems for solar fuel production.

Charge separation plays a crucial role in determining the solar-to-hydrogen conversion efficiency for photoelectrochemical water splitting. Of the factors that affect charge separation, the anisotropic charge transport property of semiconductors shows great potential in promoting charge separation, but it has received little attention. Herein, we report BiVO4 photoanodes with predominant [010] and [121] orientations and demonstrate a crystallographic-orientation-dependent charge separation of BiVO4 for solar water oxidation. We found that a [010]-orientated BiVO4 photoanode generated a photocurrent 2.9 times that of the [121]-orientated one, owing to the significantly improved charge separation. An in-depth investigation of the surface band bending by open-circuit potential and film conductivity by contacting atomic force microscopy reveals that the higher electron mobility along the [010] direction than that of [121] accounts for the improvement in charge separation. This work offers a fundamental insight into charge separation in anisotropic photoanodes for rational design of efficient photoanodes for solar energy conversion.

Heterogeneous reaction kinetics of gaseous nitric acid (HNO3) with calcium carbonate (CaCO3) particles was investigated using a particle-on-substrate stagnation flow reactor (PS-SFR). This technique utilizes the exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO3/H2O/N2, followed by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiments were conducted at atmospheric pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter of Dp = 0.85 mum, particle loading densities 2 x 104 /= 0.06 (x3//2). In a second series of experiments, HNO3 uptake on CaCO3 particles of the same size was examined over a wide range of relative humidity, from 10 to 80%. The net reaction probability was found to increase with increasing relative humidity, from gammanet >/= 0.003 at RH = 10% to 0.21 at 80%.

Hard carbon materials derived from biomass sources, such as sucrose, glucose, cotton, holly leaf, and eggshell membrane, have been intensively investigated as anodes for SIBs because of their high capacity. [4] However, these materials usually exhibit a very low initial coulombic efficiency (ICE), which hampers their practical application. [4a,d,e] For example, Pan and co-workers fabricated hard carbon microspheres using sucrose as a precursor, and their ICE was 40%. [4a] Palacín and co-workers prepared a hard carbon material using sugar as a precursor, and its ICE was ≈62%. [5] Li et al. used carbonized eggshell membrane as an anode for sodium storage, but its ICE was 45%. [4e] Zhang and co-workers prepared a hard carbon sheet-like structure using cherry petals as the raw material and achieved ICE of 67.3%. [6] Hu and co-workers prepared a carbonized leaf membrane from natural leaf as a binder-free anode for SIBs, and this anode exhibited ICE of 74.8%. [4d] Many previous studies attribute the low ICE of hard carbon materials to their large specific surface area, which may result in side reactions with the electrolyte, and these side reactions can be reduced by surface modification, such as coating the surface with soft carbon. [7] However, some experiments have demonstrated that a low specific surface area does not necessarily result in an enhancement of the ICE. [8] For instance, Billaud and co-workers fabricated pitch-based carbon fibers with specific areas as low as 1.2 and 1 m 2 g −1 , but their ICE values were only ≈33% and 15%, respectively. [9] Cao et al. synthesized hard carbon nanoparticles and hollow carbon nanowires by pyrolysis of a polyaniline precursor at the same temperature. [10b] The surface area of the hard carbon nanoparticles (23.5 m 2 g −1 ) was 30% smaller than that of the hollow carbon nanowires (31.4 m 2 g −1 ), but the ICE of the hard carbon nanoparticles (51.6%) was only 1.2% higher than that of the hollow carbon nanowires (50.5%). Mitlin and co-workers found that although the progressively decreasing surface area (from 55 to 21 m 2 g −1 ) plays a role in the increasing ICE (from 43.9% to 60.1%) as the carbonization temperature of carbonized peat moss increases (from 600 to 1400 °C), the ICE of the optimized materials was larger than that reported for high-performance carbonaceous materials (51.6%) with lower surface areas (31.4 m 2 g −1 ). [10b,11] These results suggested that other factors are responsible for the low ICE. Hard carbon Practical application of hard carbon materials in sodium-ion batteries (SIBs) is largely limited by their low initial coulombic efficiency (ICE), which may be improved by increasing the graphitization degree. However, biomassderived hard carbon is usually nongraphitizable and extremely difficult to graphitize by direct heating even at 3000 °C. Herein, a general strategy is reported for fabricating hard carbon materials with graphite crystals at 1300 °C promoted by external graphite that serves as a crystal template for the growth of graphite cry...