Hiren Kanchanbhai Machhi

Review of Se/Te chalcogen cathodes for aqueous Zn-ion batteries, highlighting design strategies, redox mechanisms, and prospects for high-performance, safe, durable energy storage.

In the field of energy technologies, self‐charging batteries are receiving extensive attention. However, the existing technologies are highly dependent on the available sources of O₂, have long self‐charging duration, and have complex architectures. Herein, a novel ultrafast chemical self‐charging Zn‐quinhydrone polymer gel (QPG) battery, composed of acid/base free quinhydrone as a cathode material is reported. The prepared Zn–QPG battery exhibits a specific capacity of 209.7 mAh g⁻¹ at 10C rate and maintains 86.4% of the initial discharge capacity even after 3000 cycles with a high coulombic efficiency of 99.4%. The aqueous amphiphilic block co‐polymer‐driven selective oxidation of hydroquinone (HQ) to benzoquinone (BQ) compels the chemical self‐charging feature wherein the device attains ≈1.1 V within ten minutes of complete discharge. The chemical self‐charging generated a high specific capacity of 197.8 mAh g⁻¹ at 10C rate with a capacity retention of 91.2% after 100 cycles. Moreover, a flexible Zn–QPG battery also demonstrates excellent rechargeability and power‐delivering ability even in a wrist‐bend geometry. This work paves the way to develop ultrafast energy storage systems, which are not dependent on an external power supply and broaden the horizon of aqueous zinc–organic batteries.

We have synthesized three different p-type donor–acceptor π-conjugated polymers based on diethyl [2,2′:5′,2′′-terthiophene]-3′,4′-dicarboxylate, dithienopyrrolobenzothiadiazole and thieno[3,4- c ]pyrrole-4,6-dione units.

With the exploration of new building blocks, a series of small organic hole transporting materials (SOHTMs) are designed and synthesized through simple microwave irradiation and systematically investigated in solid‐state dye‐sensitized solar cells (ss‐DSCs) and perovskite solar cells (PSCs). These V‐shaped SOHTMs having A–D–A architecture are endowed with low cost, better thermal stability, and good optical and electrochemical property, which respond to low indoor light and 1 sun illumination. The SOHTMs contain dibenzothiophene (DBT) and dibenzofuran (DBF) as core donors substituted with heteroaromatic molecules like naphthalene and indole, which are coded as SPH 1–SPH 4. ss‐DSCs and PSCs with SPH 4 (with LiTFSI) as SOHTMs exhibited a power conversion efficiency (PCE) amounting to 5.2% and 15.4%, respectively, under 1 sun illumination. Moreover, the applications of ss‐DSCs and PSCs in indoor environments are studied. Due to the good match with the indoor light emitting diode (LED) source, SPH 4 delivered PCEs of 26.3% (for ss‐DSCs) and 23.9 % (for PSCs) under 1800 lux illumination, which are very close to the PCE values obtained for standard hole transporting materials (HTMs) like spiro‐OMeTAD. Thus, these new SOHTMs provide the ultimate solution for the fabrication of photovoltaic devices, resulting in superior PCE under indoor light.

Rechargeable aqueous zinc–iodine batteries (AZIBs) represent excellent zinc–iodine redox chemistry and emerged as a promising aspirant due to their high safety, low cost, ease of fabrication, and high energy density. Nevertheless, the high-dissolution-induced iodide diffusion toward the zinc anode brings the self-discharge, which governs the capacity fading and poor cycling life of the battery. Herein, a multipurpose sponge-like porous matrix of a metal–organic gel to host a substantial amount of an iodine-based catholyte and uniform distribution of iodine with controlled iodide diffusion is introduced. Limiting the iodine diffusion due to increased viscosity provides superior electrochemical performance of this promising cathode for solid-state AZIBs. As a result, AZIBs delivering high performance and long-term stability are fabricated with a capacity of 184.9 mA h g^–1 with a superior capacity retention of 95.8% even after 1500 cycles at 1 C rate. The unique concept of self-discharge protection is successfully evaluated. Prototype flexible band-aid-type AZIBs were fabricated, which delivered 166.4 mA h g^–1 capacity in the bending state, and applied to real-scale wearable applications.

Mesoscopic photovoltaic devices (MPDs) are significantly promising for sustainable light-harvesting through solid-state compact designs. Materials with multifunctional properties play a vital role in improving the processability, stability, and cost of such devices. Here, a single-route synthesized sensitizer and multifunctional organic ionic plastic crystals (OIPCs) are introduced, and OIPCs are employed as a redox couple and light-harvesting contributor as a binary sensitizer-electrolyte system enabled via energy transfer in a photovoltaic device. Materials OIPC-I, OIPC-Br, and SK4 sensitizer possess a typical N-alkyl-phenoxazine (POZ)–N-alkyl-benzimidazole (BM)-type architecture, and OIPCs hold additional iodide and bromide anions at the quaternary nitrogen of BM. OIPCs show redox potential generated from anions corresponding to I⁻/I₃ ⁻ and Br⁻/Br₃ ⁻ as well as suitable molecular energy levels due to the POZ–BM donor–acceptor pathway, which results in a self-regenerative photovoltaic response in FTO/p-TiO₂/OIPC/Pt configuration without any sensitizer. The SK4 sensitizer has suitable energy levels below the redox potential level of OIPCs, which are well regenerated by OIPCs during the photo-electricity generation in the photovoltaic device. Here, an OIPC–Br-based device with high photovoltage (0.98 (±0.02) V) and pronounced photocurrent from extra electrons gained through the POZ donor present in OIPC by the energy transfer mechanism shows 45% energy transfer towards the dye or TiO₂. The OIPC-I based device demonstrated 43% (±3) higher efficiency compared to the conventional benzimidazolium-based electrolyte due to improved photocurrent and photovoltage. Single component OIPC-I based solid-state MPD devices show excellent ∼95% stability up to 5000 h, which is more than the OIPC–Br based device.

Aqueous rechargeable zinc–iodine batteries (ARZIBs) represent a promising form of sustainable energy storage, having highly abundant and environmentally workable elements. The low utilization of solid iodine and self‐discharge due to the diffusive properties of the soluble polyiodides in aqueous media hamper the stability and device design. The concept of building a solid‐state ARZIB with self‐discharge control by limiting iodide diffusion employing solid–gel reactions with water‐based gel‐embedded I₃⁻/I⁻ in block copolymer bearing highly active iodine components is demonstrated. The catholyte gel has an amphiphilic property that provides high solubility for iodine and better ionic conductivity from the cubic microcrystalline self‐assembled structures. This gel prevents long range iodide ion diffusion in multilayer self‐assemblies of the catholyte followed by the gel electrolyte layer due to self‐trapped polyiodides at the core–shell interface and inside the hydrophobic core of micelles. By contrast, positive zinc ions easily diffuse through the hydrophilic poly(ethylene oxide)‐water‐rich channels. This solid matrix results in a discharge capacity of 210 mAh g⁻¹ (at 1 C rate) and stability with a retaining capacity of 94.3% after 500 cycles, including self‐discharge protection. The flexible module device shows excellent flexibility during deformations and the ability to power gadgets with stable performance.

Organic ionic plastic crystals (OIPCs) are synthesized through a simple metal‐free, cost‐effective approach. The strategized synchronization of electron‐rich phenoxazine with benzimidazolium iodide (OIPC‐I) and bromide (OIPC‐Br) salts lead to enhanced hole mobility and conductivity of OIPCs which is suitable for an efficient alternative to conventional organic hole transporting materials (HTMs) for stable perovskite solar cells (PSCs). The fabricated PSCs with OIPC‐I as hole transporting layer yielded a power conversion efficiency of 15.0% and 18.1% without and with additive (Li salt) respectively, which are comparable with spiro‐OMeTAD based devices prepared under similar conditions. Furthermore, the PSCs with OIPCs show good stability compared to the spiro‐OMeTAD with or without additives. Here, first time benzimidazolium‐based OIPCs have been used as an alternative organic HTM for perovskite solar cells, which opens a window for the design of effective OIPCs for highly efficient PSCs with long‐term stability.