Energy storage and conversion

Halide-based perovskite films are popular absorber materials used in solar cells, but undesired effects such as charge recombination and trapping continue to cap record conversion efficiencies. Here, the authors use femtosecond transient mid-infrared spectroscopy to elucidate electron recombination and trapping in the conduction bands of various compositions of perovskite thin films.

The efficiency of perovskite/silicon tandem solar cells is affected by silicon surface texture, however fabrication processes in solution limit surface studies. Here a perovskite layer on textured silicon is formed through a dry two-step conversion process with lead oxide sputtering and direct contact with methyl ammonium iodide.

The origin of the excellent photoluminescence properties of embedded cesium lead halide perovskite nanocrystals remains to be fully understood. Here the authors visualize lattice alignments in dual-phase Cs₄PbBr₆ and CsPb₂Br₅ composites synthesized by sonochemistry and find that the CsPbBr₃ nanocrystals are responsible for the luminescence.

Perovskites are widely studied as components of solar cells but their synthesis often involves toxic reagents. Here lead-free bismuth-based perovskites are synthesised using a non-toxic solvent and shown to achieve power conversion efficiencies of up to 1.62 % under 1 sun illumination for up to 300 h.

Antimony trisulfide is a promising light harvester for photovoltaics. Here the growth of single-crystals of antimony trisulfide on polycrystalline titania is reported to proceed via an epitaxial nucleation/growth mechanism. The resulting solar cell delivers a power conversion efficiency of 5.12%.

Chlorophyll derivatives can be applied in bio-solar cells, but their excited-state dynamics are not fully understood in this context. Here pump–probe time-resolved absorption spectroscopy measurements of chlorophyll derivatives reveal enhanced lifetimes of radical species in the presence of hydroquinone.

Organic polymers have demonstrated promise as photocatalysts, but their photocatalytic efficiencies remain relatively low. Now, borrowing principles from organic photovoltaics, heterojunctions of polymer photocatalysts and small molecule acceptors have been shown to have excellent solar hydrogen production efficiencies.

Efficient electron-hole separation and carrier utilization are key factors in photosynthetic systems. Here, the authors achieve efficient charge separation following a photogenerated hole-transfer band-trap pathway in the ternary composite Pt@NH₂-UiO-66/CdS, resulting in photocatalytic hydrogen evolution with good stability and a quantum efficiency of 40.3% at 400 nm irradiation.

Photocatalytic CO₂ reduction requires catalysts that are both active and selective. Here, a mixture of CaGa₄O₇-loaded Ga₂O₃ and CaO, decorated with Ag@Cr core-shell particles, delivers over 835 µmol h⁻¹ of CO at >95 % selectivity.

Low-bandgap polymers hold great potential for photocatalytic generation of hydrogen peroxide, but increasing catalytic activity remains challenging. Here, a solar-to-chemical conversion efficiency of 0.7 % is reached for a resorcinol-formaldehyde resin powder prepared via acid-catalyzed high-temperature hydrothermal synthesis.

Coupling the photo-oxidation of biomass-derived substrates with water splitting in a photoelectrochemical cell enables efficient hydrogen generation at the cathode. Here, a photoelectrochemical device employing a nanostructured WO₃ photoanode displays photocurrents of 6.5 mA cm⁻² through oxidation of glucose, in turn producing valuable products in the form of gluconic and glucaric acids, erythrose and arabinose.

Thermocatalytic hydrogenation holds great promise for commercial utilization of carbon dioxide, but the process is energy-intense with high temperature and pressure requirements. Here, the authors engineer a GaN_1-xO_x rhodium nanoparticle catalyst for CO₂ to CO hydrogenation that functions at temperatures as low as 170 °C.

Boron-containing materials have experimentally and theoretically been shown to be promising materials for CO₂ capture and conversion. Here, hydrogen-deficient 2D hydrogen boride sheets are shown to physisorb CO₂ and promote conversion to methane and ethane.

Dry reforming of methane into syngas typically requires high temperatures, which can cause aggregation and deterioration of the catalyst. Here, the authors report a lanthanum nickel oxide catalyst prepared by in situ hydrogen reduction of LaNi_0.05Co_0.05Cr_0.9O₃ on a LaCrO₃ perovskite support that remains stable for over 100 h at 750 °C.

Direct conversion of methane to methanol has great industrial relevance, but required high reaction temperatures can lead to overoxidation of methane to carbon dioxide. Here, methanol is synthesized by one-step reaction of methane and water over a TiO₂ catalyst in a non-thermal plasma at room temperature and atmospheric pressure, which allows to isolate carbon dioxide-free methanol.

Electrocatalytic oxygen evolution is a key reaction for water splitting, but the detailed atomic structures of single-crystal electrodes under cycling conditions are still not fully understood. Here, the authors study the oxygen evolution activity on Pt(111) during potential cycling and find that the current density reaches a maximum in the third cycle and is nine times higher than that in the initial cycle, owing to a roughened Pt(111) surface and formation of islands and atomic vacancies in the second subsurface Pt layer.

Methods to overcome the slow kinetics of the oxygen evolution reaction are desirable for a range of renewable energy technologies. Here the authors demonstrate that the rate of oxygen evolution is enhanced upon introduction of hexadecyltrimethylammonium hydroxide into the alkaline electrolyte.

Microenvironment engineering through electrolyte optimization is a promising approach to mitigate catalyst poisoning effects in electrochemical systems, but the role of electrolyte anions is not fully understood. Here, in a combined experimental-theoretical evaluation, the authors study the effects of different acidic electrolytes (pH 1) on platinum for hydrogen (HER/HOR) and oxygen electrocatalysis (ORR/OER), finding that oxygen reduction performance can be improved 4-fold using nitric rather than sulfuric acid.

Hydrogen peroxide is an industrially highly demanded chemical, but its electrochemical synthesis still suffers from sluggish kinetics and imperfect selectivity. Here, the authors report a catalyst material comprising single cobalt atoms anchored on oxygen functionalized graphene oxide that produces 1.0 mg cm⁻² h⁻¹ of H₂O₂ with high selectivity and a low onset potential.

Experimental methods to evaluate electrocatalytic performance typically only address one sample at a time. Here the authors show that scanning electrochemical microscopy can screen product selectivity and electrocatalytic activity of CO₂ reduction catalyst arrays.

Ammonia-fed protonic ceramic fuel cells could be a more sustainable alternative than their hydrogen-fed counterparts. In this work, the authors couple an reversible ammonia catalyst with a protonic ceramic electrochemical cell, enabling cracking of ammonia into H₂ and N₂ for fuel-cell mode operation, as well as synthesis of ammonia from H₂O and N₂ in electrolysis mode operation.

Hydrogen for fuel cells is commonly stored in pressurized tanks, whereby safety and portability can be problematic. Here, a rechargeable proton exchange membrane fuel cell with an internal hydrogen storage polymer that is cyclable up to 50 times is presented.

The triple phase boundary structure in solid-oxide fuel cells largely determines the thermodynamics and kinetics of electrochemical processes therein. Here the authors use atomic-resolution microscopy and reaction dynamics simulation to reveal three discrete hydrogen oxidation reaction pathways.

Polyoxometalate based solids are promising candidates for proton-conducting electrolytes but their low durability and low proton conductivities remains an on-going challenge. Here the authors describe the preparation of polyoxometalate-based solids with much improved stability and proton conductivities.

Glucose is a promising feedstock for hydrogen production but the existing microbial reactors are expensive and suffer from low efficiencies. Here, the authors show an improved self-powered liquid catalyst fuel cell with a polymer-exchange membrane and polyoxometalate to catalyse glucose to hydrogen.

In microbial fuel cells direct electron transfer offers high energy conversion efficiency, but low concentrations of redox centers on bacterial membranes result in low power density. Here nitrogen-doping is fine tuned to match Flavin reaction sites, converting diffusive mediators to anchored redox centers toward direct electrochemistry.

Aluminum–sulfur batteries have a theoretical energy density comparable to lithium–sulfur batteries, whereas aluminum is the most abundant metal in the Earth’s crust and the least expensive metallic anode material to date. Here, the authors review experimental and computational approaches to tailor the chemical interactions between sulfur host materials and polysulfides in Al-S batteries and point towards promising future research directions.

Aluminum dual-ion batteries have attracted considerable attention due to their low cost, safety, high energy density, energy efficiency, and long cycling life. Here the authors review working principles, electrolytes, and corrosion effects of this battery type.

Lithium-ion batteries suffer from stability issues. Now, spontaneously formed, stable voids in antimony alloy anodes offer a simple remedy.

Its high nominal voltage, thermal stability, and low toxicity render LiMn₂O₄ a highly promising cathode material for lithium ion batteries, but capacity fading due to unwanted side reactions during cycling remains an issue. Here, the authors show that carbon-coating a LiMn₂O₄ cathode reduces side reactions such as manganese dissolution and manganese oxide formation, thereby improving battery cycling stability.

Bismuth fluoride is a promising cathode material for lithium ion batteries due to its high theoretical capacity and cycling stability, but low-cost production methods are needed for potential commercialization. Here, the authors report a synthetic method to grow pure BiF₃ via thermal decomposition of bismuth trifluoroacetate.

Lithium sulfur batteries are an emerging energy storage medium, but their stability in carbonate electrolyte remains hampered by side-reactions. Here, the authors show that as-produced monoclinic gamma-sulfur on activated carbon nanofibers converts to Li₂S without the formation of intermediate polysulfides, therefore eliminating irreversible side reactions and improving cycling stability.

The electronic structure evolution within a battery during cycling can provide crucial cues for its optimization, but insights on operando band structures are extremely challenging to obtain. Here, the authors determine the overall band structure of a model thin-film solid-state lithium battery via operando hard X-ray photoelectron spectroscopy, considering the cathode and anode sides.

The effect of the electric double layer with solid electrolytes remains hard to characterize. In this study, the authors show how to evaluate the electric double layer effect with various lithium solid electrolytes using a hydrogenated diamond-based transistor.

P2-Na_2/3[Fe_1/2Mn_1/2]O₂ is a promising high energy density cathode material for rechargeable sodium-ion batteries, but its poor long-term stability in the operating voltage window of 1.5–4.25 V vs Na⁺/Na hinders its commercial application. Here, the authors use a combination of electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and DFT calculations to investigate the origin of the capacity fading, which is attributed to an increase in bulk electronic resistance at high voltage that, among other factors, is nested in a structural phase transition.

The inclusion of nickel and manganese in layered sodium metal oxide cathodes for sodium ion batteries is known to improve stability, but the redox behaviour at high voltage is poorly understood. Here in situ X-ray spectroscopy studies show that the redox behaviour of oxygen anions can account for an increase in specific capacity at high voltages.

Redox flow batteries working at a neutral pH combine high stability and environmental safety, but their power output is still limited. Here, the authors present an aqueous, all-organic redox flow battery, with sulfonated tryptanthrin as an anolyte solution, reaching a cell voltage of 0.94 V.

Alloy systems like Si/FeSi₂ nano composites have great potential as stable anode materials in Li-ion batteries, but their characterization at different scales and throughout their ageing remains challenging. Here the authors use scattering and 2D/3D imaging techniques combined with modeling to elucidate morphology changes upon cycling of the anode.

Environmentally friendly binders for energy materials may improve sustainability, but can suffer from poor performance. Here a gel derived from graphene oxide and starch is used as a hybrid binder for supercapacitors, providing good rate performance and stability over 17,000 cycles.

Biosourced and biodegradable organic electrode materials are investigated for environmentally benign energy storage, but their performance at higher current density is often poor. Here, the authors construct electrodes with quinone-based species from Sepia melanin and tannins on treated carbon paper and observe electrode capacitance as high as 1355 mF cm⁻² at current densities up to 10 A g⁻¹.

Flexible supercapacitors are versatile energy storage devices owing to their light weight, flexibility and high power density. Here a scalable, flexible, tubular supercapacitor possessing the diameter of an electrical wire is presented.