Rechargeable batteries, particularly lithium-ion batteries (LIBs), have become the preferred choice for high-performance energy storage systems powering portable electronics. However, potassium-ion batteries (KIBs) are emerging as a viable alternative due to lithium's limited availability and high cost. Covalent organic frameworks (COFs), an advanced class of crystalline porous polymers, have become attractive electrodes for KIBs thanks to their great chemical stabilities and tunable electrochemical properties. In this study, an olefin-linked alkynyl-based COF containing 1,3,5-tri(arylethynyl)benzene (TAEB) and 2,4,6-trimethyl-1,3,5-triazine (TMT) units was utilized as a bulk anode material for KIBs. The TAEB-TMT-COF demonstrated a reversible capacity of 124 mAh g(-1) after 300 cycles with an efficiency of similar to 99 %. TAEB-TMT-COF also exhibited a reversible capacity of 105 mAh g(-1) after 300 cycles at a high current density of 500 mA g(-1) with similar to 99 % efficiency. The excellent performance is attributed to the chemical stability of olefin-linkage and the presence of the alkynyl groups, which aid in enhancing the binding of K-ions.

A battery cathode based on the superoxide/peroxide redox not only inherits the advantage of oxygen (O 2 ) batteries in high capacities and low costs but also overcomes the disadvantages in O 2 storage, electrolyte evaporation, and anode deactivation due to O 2 crossover. Herein, we report an enhanced potassium superoxide (KO 2 )/peroxide (K 2 O 2 ) conversion by adopting a high-donicity anion additive in the ether-based electrolyte. Such an anion was synthesized via a “Solvent-in-Anion” strategy and validated to enhance the electron donicity of the electrolyte. The use of high-donicity anion could lead to enhanced KO 2 utilization (≈90.2 %) by retarding electrode passivation and allow the full charging back of K 2 O 2 through the solution-mediated pathway without electrocatalysts. No apparent cell degradation is observed during the first 120 cycles by controlling the reversible depth-of-discharge capacity at 292 mAh g −1 within an O 2 -free region. The K−KO 2 cell delivers a high energy efficiency (>84.4 %) and a lifespan of over 1440 hours.

A K+ single cation ionic liquid (K-SCIL) contains only K+ cations. When used as an electrolyte in potassium batteries, it not only possesses the properties of conventional ionic liquids such as nonflammability, negligible vapor pressure, and good electrochemical stability but also increases the K+ transport number, which reduces concentration polarization of the electrolyte and improves the battery power performance. In this study, we report K-SCILs based on the low melting (T-m similar to 50 degrees C) potassium salt of (3-methoxypropyl)((trifluoromethyl)sulfonyl) amide (MPSA(-)). Combined with potassium bis(fluorosulfonyl)imide (KFSI), the mixture of the two salts exists as a liquid at as low as -13 degrees C, generating for the first time a room temperature K-SCIL. The phase diagram is established, and the ionic conductivities of various compositions are measured. Although the room temperature ionic conductivity is low, mild heating to 55 degrees C enhances the conductivity to > 1 mS/cm. Evidence for a strong resistance to K+ concentration gradients as well as a near unity K transport number were also found in this K-SCIL. This report hopes to serve as inspiration for the discovery of even lower melting K salts to enable low temperature K-SCIL electrolytes and to explore the benefits of SCILs in practical cells.

Developing low-melting alkali salts is of interest for both battery electrolytes and inorganic ionic liquids. In this study, we report a series of asymmetric alkali-metal sulfonamide salts based upon the (3-methoxypropyl)((trifluoromethyl)sulfonyl)amide (MPSA) anion. This family of salts features an unusual melting point trend, where the melting point of the salts decreases as the cation increases in size from Li to K but then the melting point increases as the cation further increases in size from K to Cs. Analyses of single crystals reveal that the unusual higher melting points of RbMPSA and CsMPSA in comparison to KMPSA can be attributed to the greater cation-cation distances as well as the increased rigidity of anion-cation coordination due to an increase in cyclic structures in comparison to KMPSA. Exceptionally, KMPSA features a very low melting point of only 50.79 ± 0.31 °C. This low melting point can be attributed to a relatively high degree of disorder, an unusual uncoordinated ether moiety, and a very short K-K distance of only 3.4348(7) Å among other factors, which is supported by the low cohesive energy and small elastic moduli among the rest according to density functional theory (DFT) calculations. The low melting point of KMPSA makes it interesting for low-temperature ionic liquids.

The development of high-performance organic electrodes for potassium-ion batteries (KIBs) is attracting interest due to their sustainability and low costs. However, the electrolyte systems and moieties that generally proved to be successful in high-performance Li-ion batteries have found relatively little success in KIBs. Herein, two alkynyl-based covalent organic frameworks (COFs) containing 1,3,5-tris(arylethynyl)benzene (TAEB) and dehydrobenzoannulene (DBA) units are utilized as bulk anode materials for KIBs in a localized high-concentration electrolyte. TAEB-COF provides a high capacity value of 254.0 mAh g-1 at ∼100% efficiency after 300 cycles, and DBA-COF 3 provides a capacity of 76.3 mAh g-1 with 98.7% efficiency after 300 cycles. DFT calculations suggest that the alkynyl units of TAEB-COF facilitate the binding of K-ions through both enthalpic and geometric driving forces, leading to high reversible capacities.

Potassium batteries have recently attracted the attention of many researchers. To date, however, most common K ion electrolytes for potassium secondary batteries are still liquid electrolytes, which may give rise to safety problems. In this work, a new single potassium-ion conducting polymer, potassium poly((trifluoromethypsulfonyl)(4-vinylphenypamide (KPSTFSA), was synthesized via a facile method. The electrolyte, which is composed of dimethoxyethane (DME)-swollen KPSTFSA with Al2O3 filler electrolyte, has a high ionic conductivity of 6.0 x 10(-2) mS cm(-1) at 20 degrees C and high potassium ion transference number of 0.87. On the contrary, traditional KPF6-DME liquid electrolyte only shows an ion transference number of 0.11. The electrochemical stability of the polymer gel electrolyte was systematically studied by using KC8. The decomposition products were characterized to illustrate the degradation mechanism. We conclude that the polystyrene structure of KPSTFSA is the most unstable motif of the molecule and readily reacts with KC8.

A redox-active dehydrobenzoannulene (DBA) monomer was used to construct an efficient porous polymer-based anode material for lithium ion batteries (LIBs).

In the past 20 years, research in metal-O2 batteries has been one of the most exciting interdisciplinary fields of electrochemistry, energy storage, materials chemistry, and surface science. The mechanisms of oxygen reduction and evolution play a key role in understanding and controlling these batteries. With intensive efforts from many prominent research groups, it becomes clear that the instability of superoxide in the presence of Li ions (Li+) and Na ions (Na+) is the fundamental root cause for the poor stability, reversibility, and energy efficiency in aprotic Li-O2 and Na-O2 batteries. Stabilizing superoxide with large K ions (K+) provides a simple but elegant solution. Superoxide-based K-O2 batteries, invented in 2013, adopt the one-electron redox process of O2/potassium superoxide (KO2). Despite being the youngest metal-O2 technology, K-O2 is the most promising rechargeable metal-air battery with the combined advantages of low costs, high energy efficiencies, abundant elements, and good energy densities. However, the development of the K-O2 battery has been overshadowed by Li-O2 and Na-O2 batteries because one might think K-O2 is just an analogous extension. Moreover, due to the lower specific energy and the high reactivity of K metal, K-O2 is often underestimated and deemed unsuitable for practical applications. The objective of this Perspective is to highlight the unique advantages of K-O2 chemistry and to clarify the misconceptions prompted by the name "superoxide" and the judgment bias based on the claimed theoretical specific energies. We will also discuss the current challenges and our perspectives on how to overcome them.

To meet the ever-increasing worldwide energy consumption, artificial photosynthesis that converts sustainable solar energy into value-added products has been widely investigated. Compared with well-studied water splitting and CO2 reduction, hydrogen peroxide (H2O2) production from photo-electrosynthesis is a lesser-known process. H2O2, as a commodity chemical, has substantial applications in the chemical industry. In recent years, attention has been focused on clean and efficient H2O2 production inspired by the development of electrocatalysis and solar cells. Different from the traditional anthraquinone (AQ) process, photoelectrochemical (PEC) systems allow for on-site production of H2O2 that can be directly utilized without the concerns of transportation and contamination. By reducing dissolved O2 in electrolytes, H2O2 can be produced on photocathodes or tandem electrodes under light illumination. This chapter summarizes recent advanced photoelectrode materials that can selectively produce H2O2 in PEC O2 reduction system and unassisted fuel cell configuration, which paves the way for developing efficient, robust photovoltaic systems suitable for sustainable energy conversion.

Highly concentrated electrolytes exhibit advantages in enhanced stability, low solvent volatility, and superior battery safety. It is therefore important to design salts that push the limit of solubility. Herein, a solvent-in-anion design of potassium salts is proposed, in which a solvent moiety is grafted onto a symmetric anion to form a new asymmetric anion possessing the structural features of the solvent. Guided by the like-dissolves-like rule, the resultant new salts exhibit record high solubilities. Moreover, by solving the crystal structures of these new salts, we suggest that the solvation structures around K+ ions in these crystals may provide hints of the solvation structures in solvent-lean concentrated electrolytes. In this work, we have demonstrated this concept by grafting ether solvent moieties onto trifluoromethylsulfonamide to form potassium asymmetric salts. The solubility in dimethylethane reaches an unprecedent mole fraction of 0.6. The resultant concentrated electrolyte increases the positive electrochemical stability to >7 V vs K+/K and improves the cycle life of potassium-oxygen batteries with reduced overpotentials. Moreover, single-crystal X-ray diffraction of these salts reveals a rich variety of coordination motifs with coordination numbers ranging from 5 to 8 and extensive multidentate and bridging interactions from all the possible coordinating atoms on the anion. Our solvent-in-anion design represents a new approach that utilizes crystal structures to probe the solvation structures in liquid and the revealed rich variety of solvation structures are of use to the experimental and theoretical modeling of concentrated electrolytes.

Rechargeable potassium batteries, including the potassium-oxygen (K-O2) battery, are deemed as promising low-cost energy storage solutions. Nevertheless, the chemical stability of the K metal anode remains problematic and hinders their development. In the K-O2 battery, the electrolyte and dissolved oxygen tend to be reduced on the K metal anode, which consumes the active material continuously. Herein, an artificial protective layer is engineered on the K metal anode via a one-step method to mitigate side reactions induced by the solvent and reactive oxygen species. The chemical reaction between K and SbF3 leads to an inorganic composite layer that consists of KF, Sb, and KSb xF y on the surface. This in situ synthesized layer effectively prevents K anode corrosion while maintaining good K+ ionic conductivity in K-O2 batteries. Protection from O2 and moisture also ensures battery safety. Improved anode life span and cycling performance (>30 days) are further demonstrated. This work introduces a novel strategy to stabilize the K anode for rechargeable potassium metal batteries.