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Supercapacitor miniaturization is highly sought after due to the considerable demand for portable, flexible, and wearable microscale electronics. Constructing supercapacitor devices in micro- and nano-scale dimensions, however, poses significant conceptual and technical challenges. We report an in-plane nickel–ruthenium/ruthenium-oxide (NiRu/RuO2) nano-supercapacitor fabricated by the focused ion beam (FIB) technique. The FIB-patterned nano-supercapacitor exhibits interdigitated microscale electrodes separated by extremely small, 100 nm, spacings and a thin (200 nm) electrodeposited NiRi/RuO2 layer. An aqueous device exhibited high areal capacitance (10.5 mF cm−2) at high scan rates, low equivalent series resistance (0.047 Ω cm2), good capacitance retention, and a power density of 625 mW cm−2 with an energy density of 0.8 μW h cm−2. A NiRu/RuO2 nano-supercapacitor containing a polymer gel electrolyte was also prepared, demonstrating the practical applicability of the technology. Notably, the FIB-fabricated NiRu/RuO2 nano-supercapacitor featured high frequency response and alternating current (AC)-line filtering capabilities, making the device the smallest supercapacitor AC line-filter reported. The new FIB-fabricated NiRu/RuO2 nano-supercapacitor design may open new avenues in nano- and micro-scale energy storage, power conditioning, and AC line filtering. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) batteries hold promise as a large‐scale energy storage solution, but their progress has been hindered by the lack of high‐performance cathodes. Here, we address this challenge by unlocking the reversible four‐electron Te0/Te4+ conversion in elemental Te, enabling the demonstration of superior Mg//Te dual‐ion batteries. Specifically, the classic magnesium aluminum chloride complex (MACC) electrolyte is tailored by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), which initiates the Te0/Te4+ conversion with two distinct charge‐storage steps. Te cathode undergoes Te/TeCl4 conversion involving Cl− as charge carriers, during which a tellurium subchloride phase is presented as an intermediate. Significantly, the Te cathode achieves a high specific capacity of 543 mAh gTe−1 and an outstanding energy density of 850 Wh kgTe−1, outperforming most of the previously reported cathodes. Our electrolyte analysis indicates that the addition of Mg(TFSI)2 reduces the overall ion‐molecule interaction and mitigates the strength of ion‐solvent aggregation within the MACC electrolyte, which implies the facilized Cl− dissociation from the electrolyte. Besides, Mg(TFSI)2 is verified as an essential buffer to mitigate the corrosion and passivation of Mg anodes caused by the consumption of the electrolyte MgCl2 in Mg//Te dual‐ion cells. These findings provide crucial insights into the development of advanced Mg‐based dual‐ion batteries. [ABSTRACT FROM AUTHOR]

Due to the drastic required thermodynamical requirements, a photoelectrode material that can function as both a photocathode and a photoanode remains elusive. In this work, we demonstrate for the first time that, under simulated solar light and without co‐catalysts, donor‐acceptor conjugated acetylenic polymers (CAPs) exhibit both impressive oxygen evolution (OER) and hydrogen evolution (HER) photocurrents in alkaline and neutral medium, respectively. In particular, poly(2,4,6‐tris(4‐ethynylphenyl)‐1,3,5‐triazine) (pTET) provides a benchmark OER photocurrent density of ~200 μA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) at pH 13 and a remarkable HER photocurrent density of ~190 μA cm−2 at 0.3 V vs. RHE at pH 6.8. By combining theoretical investigations and electrochemical‐operando Resonance Raman spectroscopy, we show that the OER proceeds with two different mechanisms, with the electron‐depleted triple bonds acting as single‐site OER in combination with the C4‐C5 atoms of the phenyl rings as dual sites. The HER, instead, occurs via an electron transfer from the tri‐acetylenic linkages to the triazine rings, which act as the HER active sites. This work represents a novel application of organic‐based materials and contributes to the development of high‐performance photoelectrochemical catalysts for the solar fuels' generation. [ABSTRACT FROM AUTHOR]

Constructing dual‐ion energy storage devices using anion‐intercalation graphite cathodes offers the unique opportunity to simultaneously achieve high energy density and output power density. However, a critical challenge remains in the lack of proper anodes that match with graphite cathodes, particularly in sustainable electrolyte systems using abundant potassium. Here, a surface grafting approach utilizing multifunctional azobenzene sulfonic acid is reported, which transforms V2C MXene into a high‐kinetics K+‐intercalation anode (denoted ASA‐V2C) for dual‐ion energy storage devices. Importantly, the grafted azobenzene sulfonic acid offers extra K+‐storage centers and fast K+‐hopping sites, while concurrently acting as a buffer between V2C layers to mitigate the structural distortion during K+ intercalation/de‐intercalation. These functionalities enable the V2C electrode with significantly enhanced specific capacity (173.9 mAh g−1 vs 121.5 mAh g−1 at 0.05 A g−1), rate capability (43.1% vs 12.0% at 20 A g−1), and cycling stability (80.3% vs 45.2% after 900 cycles at 0.05 A g−1). When coupled with an anion‐intercalation graphite cathode, the ASA‐V2C anode demonstrates its potential in a dual‐ion energy storage device. Notably, the device depicts a maximum energy density of 175 Wh kg−1 and a supercapacitor‐comparable power density of 6.5 kW kg−1, outperforming recently reported Li+‐, Na+‐, and K+‐based dual‐ion devices. [ABSTRACT FROM AUTHOR]

Sulfur is one of the most abundant and economical elements in the p‐block family and highly redox active, potentially utilizable as a charge‐storing electrode with high theoretical capacities. However, its inherent good solubility in many electrolytes inhibits its accessibility as an electrode material in typical metal‐sulfur batteries. In this work, the synthetically designed fluorinated porous polymer, when treated with elemental sulfur through a well‐known nucleophilic aromatic substitution mechanism (SNAr), allows for the covalent integration of polysulfides into a highly conjugated benzimidazole polymer by replacing the fluorine atoms. Chemically robust benzimidazole linkages allow such harsh post‐synthetic treatment and facilitate the electronic activation of the anchored polysulfides for redox reactions under applied potential. The electrode amalgamated with sulfurized polymer mitigates the so‐called polysulfide shuttle effect in the lithium‐sulfur (Li−S) battery and also enables a reversible, more environmentally friendly, and more economical aluminum‐sulfur (Al−S) battery that is configured with mostly p‐block elements as cathode, anode, and electrolytes. The improved cycling stabilities and reduction of the overpotential in both cases pave the way for future sustainable energy storage solutions. [ABSTRACT FROM AUTHOR]

Correction for 'A focused ion beam-fabricated high-performance electrodeposited nickel–ruthenium–ruthenium oxide nano-supercapacitor' by Sudipta Biswas et al., J. Mater. Chem. A, 2024, 12, 20887–20893, https://doi.org/10.1039/D4TA03734K. [ABSTRACT FROM AUTHOR]

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Construction of structurally defined, patterned metal films is a fundamental objective in the emerging and active field of bottom-up nanotechnology. A new strategy for constructing macroscopically organized Au nanostructured films is presented. The approach is based upon a novel phenomenon in which incubation of water-soluble Au(SCN)41− complex with amine-displaying surfaces gives rise to spontaneous crystallization and concurrent reduction, resulting in the formation of patterned metallic gold films. The Au films exhibit unique nanoribbon morphology, likely corresponding to aurophilic interactions between the complex moieties anchored to the amine groups through electrostatic attraction. Critically, no external reducing agents are needed to initiate or promote formation of the metallic Au films. In essence, the thiocyanate ligands provide the means for surface targeting of the complex, guide the Au crystallization process and, importantly, donate the reducing electrons. It is shown that the Au films exhibit electrical conductivity and high transparency over a wide spectral range, lending the new approach to possible applications in optoelectronics, catalysis, and sensing. In a broader context, a new gold chemistry route is presented in which ligand-enabled crystallization/reduction could open the way to a wealth of innovative reaction pathways and applications. [ABSTRACT FROM AUTHOR]

The lower performance of pseudocapacitive supercapacitors in high‐frequency applications such as alternating current (AC) line filtering has been ascribed to presumed slow kinetics of redox processes compared to ion diffusion in electric double layer capacitors. A nickel‐deposited ruthenium/ruthenium‐oxide symmetric supercapacitor exhibiting remarkable electrochemical properties, particularly very high frequency response (>1 kHz) is developed. The electrodes are prepared via a simple process consisting of electrochemical reduction of ruthenium chloride on commercially available nickel foil as the current collector. A symmetric supercapacitor comprising nickel/ruthenium/ruthenium‐oxide electrodes and a polystyrene‐based thin spacer exhibits particularly fast scan rates, high power density of 1500 mW cm−2 (88 kW cm−3) with a maximum energy density of 0.58 µWh cm−2 (34 mWh cm−3), and excellent capacitance retention. Notably, supercapacitors prepared by the same synthetic method albeit using conventional gold substrate instead of nickel exhibit significantly lower frequency response. The exceptional electrochemical properties of the nickel/ruthenium/ruthenium‐oxide supercapacitor and simple electrode synthesis point to promising applicability in AC line filtering and power conditioning. In a broader context, this work demonstrates that, contrary to the widely held presumption, the kinetics of redox reactions at the active layers of pseudocapacitors may not be the primary barriers to high‐frequency applications. [ABSTRACT FROM AUTHOR]

The increasing demand for flexible and wearable microelectronics is a major driving force for the development of high‐performance small‐volume energy sources. Microsupercapacitors exhibit significant potential in energy storage as they provide high power and good cycle stability. Yet, most microsupercapacitors display low energy densities limiting their practical use in microelectronics. Here, synthesis of high surface area freestanding electrodes comprising hollow nickel microfibers is demonstrated. The microfiber nickel electrodes constitute a platform for flexible asymmetric microsupercapacitors exhibiting excellent mechanical resilience as well as high energy density (0.11 mWh cm−2) and power density (37.5 mW cm−2). The freestanding nature and extensive surface area of the electrodes contribute to pronounced areal and volumetric capacitance, energy storage values, and stability after numerous (hundreds) physical bending cycles. The simple preparation scheme and use of an inexpensive building block (e.g., nickel) underscore potential uses as light and flexible energy storage devices. A freestanding Ni electrode composed of hollow microfibers, serving as a scaffold for high areal capacitance microsupercapacitors, is presented. Electrodes coated with either MnO2 or polypyrrole and reduced graphene oxide are fabricated and used for assembly of asymmetric, flexible microsupercapacitor with gel electrolyte. The device can be repeatedly bent and twisted while still producing excellent energy densities. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) conjugated metal-organic frameworks (c-MOFs) are promising materials for supercapacitor (SC) electrodes due to their high electrochemically accessible surface area coupled with superior electrical conductivity compared to traditional MOFs. Here, porous and non-porous HHB-Cu (HHB=hexahydroxybenzene), derived through surfactant-assisted synthesis, are studied as representative 2D c-MOF models, showing different reversible redox reactions with Na+ and Li+ in aqueous and organic electrolytes, respectively. We deployed these redox activities to design negative electrodes for hybrid SCs (HSCs), combining the battery-like property of HHB-Cu as negative electrode and the high capacitance and robust cyclic stability of activated carbon (AC) as positive electrode. In organic electrolyte, porous HHB-Cu-based HSC achieves a maximum cell specific capacity (Cs) of 22.1 mAhg-1 at 0.1 Ag-1, specific energy (Es) of 15.55 Whkg-1 at specific power (Ps) of 70.49 Wkg-1, and 77% cyclic stability after 3000 gravimetric charge-discharge (GCD) cycles at 1 Ag-1 (calculated on the mass of both electrode materials). In the aqueous electrolyte, porous HHB-Cu-based HSC displays a Cs of 13.9 mAhg-1 at 0.1 Ag-1, Es of 6.13 Whkg-1 at 44.05 Wkg-1, and 72.3% Cs retention after 3000 GCD cycles. The non-porous sample shows lower Es performance but better rate capability compared to the porous one., (© 2024 Wiley‐VCH GmbH.)

Sulfur is one of the most abundant and economical elements in the p-block family and highly redox active, potentially utilizable as a charge-storing electrode with high theoretical capacities. However, its inherent good solubility in many electrolytes inhibits its accessibility as an electrode material in typical metal-sulfur batteries. In this work, the synthetically designed fluorinated porous polymer, when treated with elemental sulfur through a well-known nucleophilic aromatic substitution mechanism (S N Ar), allows for the covalent integration of polysulfides into a highly conjugated benzimidazole polymer by replacing the fluorine atoms. Chemically robust benzimidazole linkages allow such harsh post-synthetic treatment and facilitate the electronic activation of the anchored polysulfides for redox reactions under applied potential. The electrode amalgamated with sulfurized polymer mitigates the so-called polysulfide shuttle effect in the lithium-sulfur (Li-S) battery and also enables a reversible, more environmentally friendly, and more economical aluminum-sulfur (Al-S) battery that is configured with mostly p-block elements as cathode, anode, and electrolytes. The improved cycling stabilities and reduction of the overpotential in both cases pave the way for future sustainable energy storage solutions., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Emerging rechargeable aluminium batteries (RABs) offer a sustainable option for next-generation energy storage technologies with low cost and exemplary safety. However, the development of RABs is restricted by the limited availability of high-performance cathode materials. Herein, we report two polyimide two-dimensional covalent organic frameworks (2D-COFs) cathodes with redox-bipolar capability in RAB. The optimal 2D-COF electrode achieves a high specific capacity of 132 mAh g -1 . Notably, the electrode presents long-term cycling stability (with a negligible ≈0.0007 % capacity decay per cycle), outperforming early reported organic RAB cathodes. 2D-COFs integrate n-type imide and p-type triazine active centres into the periodic porous polymer skeleton. With multiple characterizations, we elucidate the unique Faradaic reaction of the 2D-COF electrode, which involves AlCl 2+ and AlCl 4 - dual-ions as charge carriers. This work paves the avenue toward novel organic cathodes in RABs., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)