Tin Halide Perovskites: Progress and Challenges

The chemical composition engineering of lead halide perovskites via a partial or complete replacement of toxic Pb with tin has been widely reported as a feasible process due to the suitable ionic radius of Sn and its possibility of existing in the +2 state. Interestingly, a complete replacement narrows the bandgap while a partial replacement gives an anomalous phenomenon involving a further narrowing of bandgap relative to the pure Pb and Sn halide perovskite compounds. Unfortunately, the merits of this anomalous behavior have not been properly harnessed. Although promising progress has been made to advance the properties and performance of Sn‐based perovskite systems, their photovoltaic (PV) parameters are still significantly inferior to those of the Pb‐based analogs. This review summarizes the current progress and challenges in the preparation, morphological and photophysical properties of Sn‐based halide perovskites, and how these affect their PV performance. Although it can be argued that the Pb halide perovskite systems may remain the most sought after technology in the field of thin film perovskite PV, prospective research directions are suggested to advance the properties of Sn halide perovskite materials for improved device performance.     

Affinity Laminated Chromatography Membrane Built‐in Electrodes for Suppressing Polysulfide Shuttling in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising candidates for energy storage, but suffer from capacity and cycling challenges caused by the serious shuttling effect of polysulfide (PS) ions. To address these issues, a sodium alginate (SA)‐derived affinity laminated chromatography membrane built‐in electrode is designed. This is the first attempt to utilize this type of membrane, which is widely used for the selective adsorption of proteins, in the battery field. An ordered multilayer structure throughout the electrode can easily be obtained, and the number of membrane layers can be also conveniently controlled by varying the cross‐linking time of SA. The PS shuttling effect is efficiently suppressed and the permeability of PSs is reduced by enveloping the carbon/sulfur powder in ultrathin laminated chromatography membranes. As a result, these designed electrodes deliver a superhigh initial capacity of 1492 mA h g^?1, with a capacity retention almost 20% higher than the contrast. This low‐cost and easily mass‐producible strategy inspired by affinity chromatography is expected to effectively solve the PS shuttling problem toward high‐loading and long‐lifetime Li–S batteries in practice.     

Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability

In this progress report, recent improvements to the room temperaturesyntheses of lead halide perovskite nanocrystals (APbX₃, X = Cl, Br, I) are assessed, focusing on various aspects which influence the commercial viability of the technology. Perovskite nanocrystals can be prepared easily from low‐cost precursors under ambient conditions, yet they have displayed near‐unity photoluminescence quantum yield with narrow, highly tunable emission peaks. In addition to their impressive ambipolar charge carrier mobilities, these properties make lead halide perovskite nanocrystals very attractive for light‐emitting diode (LED) applications. However, there are still many practical hurdles preventing commercialization. Recent developments in room temperature synthesis and purification protocols are reviewed, closely evaluating the suitability of particular techniques for industry. This is followed by an assessment of the wide range of ligands deployed on perovskite nanocrystal surfaces, analyzing their impact on colloidal stability, as well as LED efficiency. Based on these observations, a perspective on important future research directions that can expedite the industrial adoption of perovskite nanocrystals is provided.     

Half‐Heusler Thermoelectric Module with High Conversion Efficiency and High Power Density

Half‐Heusler (HH) compounds have shown great potential in waste heat recovery. Among them, p‐type NbFeSb and n‐type ZrNiSn based alloys have exhibited the best thermoelectric (TE) performance. However, TE devices based on NbFeSb‐based HH compounds are rarely studied. In this work, bulk volumes of p‐type (Nb_0.8Ta_0.2)_0.8Ti_0.2FeSb and n‐type Hf_0.5Zr_0.5NiSn_0.98Sb_0.02 compounds are successfully prepared with good phase purity, compositional homogeneity, and matchable TE performance. The peak zTs are higher than 1.0 at 973 K for Hf_0.5Zr_0.5NiSn_0.98Sb_0.02 and at 1200 K for (Nb_0.8Ta_0.2)_0.8Ti_0.2FeSb. Based on an optimal design by a full‐parameters 3D finite element model, a single stage TE module with 8 n‐p HH couples is assembled. A high conversion efficiency of 8.3% and high power density of 2.11 W cm^?2 are obtained when hot and cold side temperatures are 997 and 342 K, respectively. Compared to the previous TE module assembled by the same materials, the conversion efficiency is enhanced by 33%, while the power density is almost the same. Given the excellent mechanical robustness and thermal stability, matchable thermal expansion coefficient and TE properties of NbFeSb and ZrNiSn based HH alloys, this work demonstrates their great promise for power generation with both high conversion efficiency and high power density.     

Enhanced Kinetics Harvested in Heteroatom Dual‐Doped Graphitic Hollow Architectures toward High Rate Printable Potassium‐Ion Batteries

Carbonaceous materials have emerged as promising anode candidates for potassium‐ion batteries (PIBs) due to overwhelming advantages including cost‐effectiveness and wide availability of materials. However, further development in this realm is handicapped by the deficiency in their in‐target and large‐scale synthesis, as well as their low specific capacity and huge volume expansion. Herein the precise and scalable synthesis of N/S dual‐doped graphitic hollow architectures (NSG) via direct plasma enhanced chemical vapor deposition is reported. Thus‐fabricated NSG affording uniform nitrogen/sulfur co‐doping, possesses ample potassiophilic surface moieties, effective electron/ion‐transport pathways, and high structural stability, which bestow it with high rate capability (≈100 mAh g^?1 at 20 A g^?1) and a prolonged cycle life (a capacity retention rate of 90.2% at 5 A g^?1 after 5000 cycles), important steps toward high‐performance K‐ion storage. The enhanced kinetics of the NSG anode are systematically probed by theoretical simulations combined with operando Raman spectroscopy, ex situ X‐ray photoelectron spectroscopy, and galvanostatic intermittent titration technique measurements. In further contexts, printed NSG electrodes with tunable mass loading (1.84, 3.64, and 5.65 mg cm^?2) are realized to showcase high areal capacities. This study demonstrates the construction of a printable carbon‐based PIB anode, that holds great promise for next‐generation grid‐scale PIB applications.     

Boosting Superior Lithium Storage Performance of Alloy‐Based Anode Materials via Ultraconformal Sb Coating–Derived Favorable Solid‐Electrolyte Interphase

Alloy materials such as Si and Ge are attractive as high‐capacity anodes for rechargeable batteries, but such anodes undergo severe capacity degradation during discharge–charge processes. Compared to the over‐emphasized efforts on the electrode structure design to mitigate the volume changes, understanding and engineering of the solid‐electrolyte interphase (SEI) are significantly lacking. This work demonstrates that modifying the surface of alloy‐based anode materials by building an ultraconformal layer of Sb can significantly enhance their structural and interfacial stability during cycling. Combined experimental and theoretical studies consistently reveal that the ultraconformal Sb layer is dynamically converted to Li₃Sb during cycling, which can selectively adsorb and catalytically decompose electrolyte additives to form a robust, thin, and dense LiF‐dominated SEI, and simultaneously restrain the decomposition of electrolyte solvents. Hence, the Sb‐coated porous Ge electrode delivers much higher initial Coulombic efficiency of 85% and higher reversible capacity of 1046 mAh g^?1 after 200 cycles at 500 mA g^?1, compared to only 72% and 170 mAh g^?1 for bare porous Ge. The present finding has indicated that tailoring surface structures of electrode materials is an appealing approach to construct a robust SEI and achieve long‐term cycling stability for alloy‐based anode materials.     

Revisiting the Role of Conductivity and Polarity of Host Materials for Long‐Life Lithium–Sulfur Battery

Despite their high theoretical energy density and low cost, lithium–sulfur batteries (LSBs) suffer from poor cycle life and low energy efficiency owing to the polysulfides shuttle and the electronic insulating nature of sulfur. Conductivity and polarity are two critical parameters for the search of optimal sulfur host materials. However, their role in immobilizing polysulfides and enhancing redox kinetics for long‐life LSBs are not fully understood. This work has conducted an evaluation on the role of polarity over conductivity by using a polar but nonconductive platelet ordered mesoporous silica (pOMS) and its replica platelet ordered mesoporous carbon (pOMC), which is conductive but nonpolar. It is found that the polar pOMS/S cathode with a sulfur mass fraction of 80 wt% demonstrates outstanding long‐term cycle stability for 2000 cycles even at a high current density of 2C. Furthermore, the pOMS/S cathode with a high sulfur loading of 6.5 mg cm^?2 illustrates high areal and volumetric capacities with high capacity retention. Complementary physical and electrochemical probes clearly show that surface polarity and structure are more dominant factors for sulfur utilization efficiency and long‐life, while the conductivity can be compensated by the conductive agent involved as a required electrode material during electrode preparation. The present findings shed new light on the design principles of sulfur hosts towards long‐life and highly efficient LSBs.     

Ruthenium Triazine Composite: A Good Match for Increasing Hydrogen Evolution Activity through Contact Electrification

The development of Pt‐free catalysts for the alkaline hydrogen evolution reaction (HER), which is widely used in industrial scale water‐alkali electrolyzers, remains a contemporary and pressing challenge. Ruthenium (Ru) has excellent water‐dissociation abilities and could be an alternative water splitting catalyst. However, its large hydrogen binding energy limits HER activity. Here, a new approach is proposed to boost the HER activity of Ru through uniform loading of Ru nanoparticles on triazine‐ring (C₃N₃)‐doped carbon (triNC). The composite (Ru/triNC) exhibits outstanding HER activity with an ultralow overpotential of ≈2 mV at 10 mA cm^?2; thereby making it the best performing electrocatalyst hitherto reported for alkaline HER. The calculated metal mass activity of Ru/triNC is >10 and 15 times higher than that of Pt/C and Pt/triNC. Both theoretical and experimental studies reveal that the triazine‐ring is a good match for Ru to weaken the hydrogen binding on Ru through interfacial charge transfer via increased contact electrification. Therefore, Ru/triNC can provide the optimal hydrogen adsorption free energy (approaching zero), while maintaining the strong water‐dissociation activity. This study provides a new avenue for designing highly efficient and stable electrocatalysts for water splitting.