The limited resources and uneven distribution of lithium stimulate strong motivation to develop new rechargeable batteries that use alternative charge carriers. Potassium-ion batteries (PIBs) are at the top of the list of alternatives because of the abundant raw materials and relatively high energy density, fast ion transport kinetics in the electrolyte, and low cost. However, several challenges still hinder the development of PIBs, such as low reversible capacity, poor rate performance, and inferior cycling stability. Research on the cathode is currently focused on developing materials with high energy density and cycling stability, mainly including layered transition metal oxides, polyanion compounds, organic compounds, etc. Anodes based on intercalation reactions, conversion reactions, and alloying with potassium are currently under development, and promising results have been published. This review comprehensively summarizes the research effort to date on the electrode material optimization (e.g., crystals, morphology, reaction mechanisms, and interface control), the synthesis methods, and the full cell fabrication for PIBs to enhance the electrochemical potassium storage and provide a platform for further development in this battery system.

Potassium-ion batteries: outlook on present and future technologies

Semiconductor photothermal materials enabling efficient solar steam generation toward desalination and wastewater treatment

The different polymorphic phases of transition metal dichalcogenides (TMDs) have attracted enormous interest in the last decade. The metastable metallic and small band gap phases of group VI TMDs displayed leading performance for electrocatalytic hydrogen evolution, high volumetric capacitance and some of them exhibit large gap quantum spin Hall (QSH) insulating behaviour. Metastable 1T(1T') phases require higher formation energy, as compared to the thermodynamically stable 2H phase, thus in standard chemical vapour deposition and vapour transport processes the materials normally grow in the 2H phases. Only destabilization of their 2H phase via external means, such as charge transfer or high electric field, allows the conversion of the crystal structure into the 1T(1T') phase. Bottom-up synthesis of materials in the 1T(1T') phases in measurable quantities would broaden their prospective applications and practical utilization. There is an emerging evidence that some of these 1T(1T') phases can be directly synthesized via bottom-up vapour- and liquid-phase methods. This review will provide an overview of the synthesis strategies which have been designed to achieve the crystal phase control in TMDs, and the chemical mechanisms that can drive the synthesis of metastable phases. We will provide a critical comparison between growth pathways in vapour- and liquid-phase synthesis techniques. Morphological and chemical characteristics of synthesized materials will be described along with their ability to act as electrocatalysts for the hydrogen evolution reaction from water. Phase stability and reversibility will be discussed and new potential applications will be introduced. This review aims at providing insights into the fundamental understanding of the favourable synthetic conditions for the stabilization of metastable TMD crystals and at stimulating future advancements in the field of large-scale synthesis of materials with crystal phase control.

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Direct synthesis of metastable phases of 2D transition metal dichalcogenides

MoS2 intrinsically show Pt-like hydrogen evolution reaction (HER) performance. Pristine MoS2 displayed low HER activity, which was caused by low quantities of catalytic sites and unsatisfactory conductivity. Then, phase engineering and S vacancy were developed as effective strategies to elevate the intrinsic HER performance. Heterojunctions and dopants were successful strategies to improve HER performance significantly. A couple of state-of-the-art MoS2 catalysts showed HER performance comparable to Pt. Applying multiple strategies in the same electrocatalyst was the key to furnish Pt-like HER performance. In this review, we summarize the available strategies to fabricate superior MoS2 HER catalysts and tag the important works. We analyze the well-defined strategies for fabricating a superior MoS2 electrocatalyst, propose complementary strategies which could help meet practical requirements, and help people design highly efficient MoS2 electrocatalysts. We also provide a brief perspective on assembling practical electrochemical systems by high-performance MoS2 electrocatalysts, apply MoS2 in other important electrocatalysis reactions, and develop high-performance two-dimensional (2D) dichalcogenide HER catalysts not limited to MoS2. This review will help researchers to obtain a better understanding of development of superior MoS2 HER electrocatalysts, providing directions for next-generation catalyst development.

Roadmap and Direction toward High-Performance MoS 2 Hydrogen Evolution Catalysts.

The intrinsic activity of in-plane chalcogen atoms plays a significant role in the catalytic performance of transition metal dichalcogenides (TMDs). A rational modulation of the local configurations is essential to activating the in-plane chalcogen atoms but restricted by the high energy barrier to break the in-plane TM-X (X = chalcogen) bonds. Here, we theoretically design and experimentally realize the tuning of local configurations. The electron transfer capacity of local configurations is used to screen suitable TMDs materials for hydrogen evolution reaction (HER). Among various configurations, the triangular-shape cobalt atom cluster with a central sulfur vacancy (3CoMo-VS) renders the distinct electrocatalytic performance of MoS2 with much reduced overpotential and Tafel slope. The present study sheds light on deeper understanding of atomic-scale local configuration in TMDs and a methodology to boost the intrinsic activity of chalcogen atoms. Designing and realizing local configurations can activate the in-plane chalcogen atoms of transition metal dichalcogenide to enhance the HER activity. We combine the theoretical screening (charge transfer capability) and experimental realization to achieve highly active local configurations

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Enhanced performance of in-plane transition metal dichalcogenides monolayers by configuring local atomic structures.

Noncentrosymmetric MoS2 semiconductors (1H, 3R) possess not only novel electronic structures of spin-orbit coupling (SOC) and valley polarization but also remarkable nonlinear optical effects. A more interesting noncentrosymmetric structure, the so-called 1T‴-MoS2 layers, was predicted to be built up from [MoS6] octahedral motifs by theoreticians, but the bulk 1T‴ MoS2 or its single crystal structure has not been reported yet. Here, we have successfully harvested 1T‴ MoS2 single crystals by a topochemical method. The new layered structure is determined from single-crystal X-ray diffraction. The crystal crystallizes in space group P31m with a cell of a = b = 5.580(2) A and c = 5.957(2) A, which is a √3 a × √3 a superstructure of 1T MoS2 with corner-sharing Mo3 triangular trimers observed by the STEM. 1T‴ MoS2 is verified to be semiconducting and possesses a band gap of 0.65 eV, different from metallic nature of 1T or 1T' MoS2. More surprisingly, the 1T‴ MoS2 does show strong optical second-harmonic generation signals. This work provides the first layered noncentrosymmetric semiconductor of edge-sharing MoS6 octahedra for the research of nonlinear optics.

Structural Determination and Nonlinear Optical Properties of New 1T‴-Type MoS2 Compound.

Rechargeable aqueous batteries have been widely investigated for large-scale energy storage in view of their high safety and low cost. While tremendous efforts have been devoted to the development of cathode materials, few have focused on the development of anode materials and only limited candidates such as V-based oxides and Ti-based polyanionic compounds have been explored. In this study, for the first time, we discover a hydrated compound of molybdenum based ternary sulfide K0.38(H2O)0.82MoS2 as a universal host for reversible intercalation of various hydrated cations (K+, Na+, Li+, NH4+, Mg2+, Al3+, etc.). It undergoes a two-phase reaction during the electrochemical process, showing a stable redox potential of around -0.1 V vs. Ag/AgCl to serve as an anode material and a specific capacity of over 50 mA h g-1 at a current density of 0.5 A g-1. The intercalation of larger hydrated cations during the discharge process results in a lower operation potential and wider interlayer spacing, which has been explained theoretically by Gibbs free energy analysis and valence bond theory. In particular, taking hydrated K+ insertion and extraction of K0.38(H2O)0.82MoS2 as an example, the ex situ XRD and XPS results demonstrate a reversible change in the phase structure and Mo3+/Mo4+ redox couple during the charge-discharge process. Our study provides a promising anode for aqueous batteries using K0.38(H2O)0.82MoS2 as a universal host.

K0.38(H2O)0.82MoS2 as a universal host for rechargeable aqueous cation (K+, Na+, Li+, NH4+, Mg2+, Al3+) batteries.

Synthesis, crystal structures and physical properties of Ax(H2O)yMoS2 (A = K, Rb, Cs)

This work reports the synthesis of a new quasi two-dimensional layered compound, K0.36(H2O)yWS2, for aqueous potassium ion storage. Its crystal structure determined by single crystal X-ray diffraction is composed of WS2 layers and disordered hydrated K+ stacking along the c direction alternately. Due to the large interlayer spacing and high conductivity, K0.36(H2O)yWS2 is demonstrated to be a stable host for reversible intercalation and de-intercalation of hydrated K+ in K2SO4 aqueous solution.

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K0.36(H2O)yWS2: a new layered compound for reversible hydrated potassium ion intercalation in aqueous electrolyte

Self-reconstruction has been considered an efficient means to prepare efficient electrocatalysts in various energy transformation process for bond activation and breaking. However, developing nano-sized electrocatalysts through complete in-situ reconstruction with improved activity remains challenging. Herein, we report a bottom-up evolution route of electrochemically reducing Cs3Rh2I9 halide-perovskite clusters on N-doped carbon to prepare ultrafine Rh nanoparticles (~2.2 nm) with large lattice spacings and grain boundaries. Various in-situ and ex-situ characterizations including electrochemical quartz crystal microbalance experiments elucidate the Cs and I extraction and Rh reduction during the electrochemical reduction. These Rh nanoparticles from Cs3Rh2I9 clusters show significantly enhanced mass and area activity toward hydrogen evolution reaction in both alkaline and chlor-alkali electrolyte, superior to liquid-reduced Rh nanoparticles as well as bulk Cs3Rh2I9-derived Rh via top-down electro-reduction transformation. Theoretical calculations demonstrate water activation could be boosted on Cs3Rh2I9 clusters-derived Rh nanoparticles enriched with multiply sites, thus smoothing alkaline hydrogen evolution. 

https://www.nature.com/articles/s41467-023-35783-y.pdf

Yuanlv Mao

Papers

Structural Determination and Nonlinear Optical Properties of New 1T‴-Type MoS2 Compound.

K0.38(H2O)0.82MoS2 as a universal host for rechargeable aqueous cation (K+, Na+, Li+, NH4+, Mg2+, Al3+) batteries.

Synthesis, crystal structures and physical properties of Ax(H2O)yMoS2 (A = K, Rb, Cs)

K0.36(H2O)yWS2: a new layered compound for reversible hydrated potassium ion intercalation in aqueous electrolyte

Bottom-up evolution of perovskite clusters into high-activity rhodium nanoparticles toward alkaline hydrogen evolution