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A comprehensive review about the recent advances of single-atom catalysts for photocatalytic and photoelectrochemical water splitting is presented by highlighting the distinctive roles, unique fabrication methods and specific design strategies.

The Li-metal anode plays a critical role in meeting the ever-growing demands for high-energy-density batteries. The rational design of an electrolyte to suppress dendrite formation is of great significance for the practical use of a Li-metal anode in rechargeable Li-metal batteries. In this work, by taking advantage of the lithiophilic polyacenequinone polymer filler, a novel polymer-filler-reinforced gel polymer electrolyte with the merits of high mechanical flexibility, high ionic conductivity, and superior dendrite-Li suppressing ability has been developed. When this gel polymer electrolyte is used in Li symmetrical cells, small and stable Li-plating/stripping overpotentials (∼25 mV) can be maintained over 700 hours. When equipped with a high-voltage cathode of LiNi0.6Co0.2Mn0.2O2 (NCM622) for Li-metal batteries, a high coulombic efficiency of about 99% can be retained after 100 repeated cycles. Such superiority is mainly ascribed to the smart lithiophilic carbonyl groups on the polyacenequinone polymer filler, which can guide uniform Li-ion flux at the Li electrode/electrolyte interface to fundamentally suppress Li dendrite growth during cycling. This work paves a way for designing dendrite-suppressed gel polymer electrolytes for Li-metal batteries and related energy conversion and storage devices.

Cost-effective electrocatalysts with high activity and long durability for the oxygen evolution reaction (OER) are key to water splitting and rechargeable metal–air batteries. Here, we report the development of a superior OER electrocatalyst with outstanding activity, favorable durability, and stable particulate morphology based on an ex situ ultra-fast cation exchange strategy that can result in fine tuning of the atom arrangement inside the oxide lattice, thus optimizing the electrocatalytic performance. O3-phase NaCo0.8Fe0.2O2 (O-NCF) is selected as the starting material, and the sodium in the oxide lattice is rapidly exchanged (several minutes) with hydronium ions (H3O+) in an acidic solution. The as-derived structure fine-tuned sample displays excellent OER performances in alkaline media with an ultra-low overpotential of only 234 mV at 10 mA cm−2 in oxide-based electrocatalysts and an ultra-small Tafel slope of 34 mV dec−1. The exchange of H3O+ with Na+ does not affect the oxidation state of cobalt and iron cations inside the oxide lattice, while protons in the inserted H3O+ promote the formation of the hydroxyl group to improve activity. As a general strategy, such cation exchange strategy can also be applied to many other layered sodium transition metal oxides.

Lithium–sulfur (Li–S) batteries are of great interest due to their high theoretical energy density and potentially low cost. However, two of the key issues hindering their commercialization are the polysulfide shuttling and Li-dendrite growth, which result in severe capacity decay and serious safety hazards. Herein, liquid-phase delaminated birnessite (HxMnO2+x) nanosheets along with graphene and carbon nanotubes are utilized for the first time to create an “electronegative” coating layer for Li–S batteries to suppress the polysulfide shuttling and Li-dendrite growth. The as-prepared coating layer enables stable cycling of the Li–S battery with a low capacity decay rate of 0.04% per cycle over 1000 cycles at 1C. In addition, a Li-symmetrical cell with the coating layer shows suppressed dendrite growth even after being cycled over 1000 hours at 1 mA cm−2. This excellent performance is ascribed, in part, to the synergistic effect of the chemical and electrostatic interactions among polysulfides, Li ions, and [MnO2+x]x− ions, resulting in a homogeneous Li-ion flux distribution and a mitigated polysulfide shuttling. The proposed concept of an “electronegative” bifunctional coating layer illustrates a simple and effective way to develop highly stable and safe Li–S batteries.

The feasibility of renewable acetic acid as a direct fuel of SOFCs for sustainable electric power generation was investigated. To solve the problem of carbon deposition over conventional nickel cermet anodes, an advanced catalyst for acetic acid catalytic decomposition/internal reforming reaction was exploited. A comparative study of coke formation over Ni/Al2O3, Ni/MgO–Al2O3 and Ni–YSZ catalysts was conducted by oxygen-temperature programmed oxidation analysis. We found that the Ni/MgO–Al2O3 catalyst is much superior to the other two catalysts in suppressing carbon deposition, especially under the condition of the presence of steam in the acetic acid fuel. Various cells were fabricated and tested under different conditions. The differences in OCVs and power outputs of the cells caused by the usage of hydrogen and acetic acid as fuels were studied and explained based on the thermodynamic calculation and EIS measurement. After optimization, a peak power density of 1325 mW cm−2 at a furnace temperature of 800 °C was achieved for the cell with a catalyst layer operating on acetic acid fuel. The cell was successfully operated continuously on acetic acid–steam fuel for a period of at least 200 h without any noticeable performance degradation, delamination of the catalyst layer and carbon deposition. The promising results of this work show the possibility of better utilization of the abundant bio-mass or bio-oil for future energy generation.

To develop high-power and fast energy storage devices, electrode materials with superior ionic and electronic transport properties should be developed. Herein, a novel composite electrode with TiO2 nanotubes connected onto a conductive carbon nanofiber network is designed and realized through a general route. The carbon matrix is first synthesized using an electrospinning technique and heat-treatment, and the embedded rutile TiO2 nanoparticles are formed in situ as the starting materials for the hydrothermal reaction. After hydrothermal treatment, a three-dimensional (3D) porous architecture is developed. The mechanistic analysis demonstrates that the raw embedded rutile TiO2 nanoparticles react with NaOH solution and go out around the carbon nanofiber matrix to form a well-connected 3D porous nanotube/nanofiber architecture. By using the as-prepared films as electrodes for lithium-ion batteries (LIBs) without the application of any additional conductive agent or binder, high initial capacity and excellent rate performance (214 mA h g−1 at 5 C rate, 180 mA h g−1 at 10 C rate, 138 mA h g−1 at 20 C rate and 112 mA h g−1 at 30 C rate) are achieved. Moreover, the electrode shows stable cycling performance, especially at a high rate of 30 C, without undergoing decay after 1000 cycles.

As a lithium-intercalation material, high crystallinity is important for Li4Ti5O12 to achieve good capacity and cycling stability, while a large surface area and a short lithium diffusion distance are critical to increase rate capacity. In this study, well-crystallized Li4Ti5O12 nanoplates with outstanding electrochemical performance were facially prepared through a two-step hydrothermal preparation with benzyl alcohol–NH3·H2O (BN) as the solvent and a subsequent intermediate-temperature calcination at 500 °C for 2 h in air. To support the superiority of benzyl alcohol–NH3·H2O (BN) for hydrothermal synthesis, ethanol–NH3·H2O (EN) was also comparatively studied as solvent. In addition, different hydrothermal reaction times were tried to locate the optimal reaction time. The nature of as-prepared Li4Ti5O12–BN (LTO–BN) and Li4Ti5O12–EN (LTO–EN) was characterized by XRD, N2 adsorption/desorption tests, SEM, TEM and TGA-DSC. Compared with EN, the BN hydrothermal solvent facilitated the formation of nanosheet-Li4Ti5O12 with wall thicknesses of 8–15 nm and better crystallization. After a 6 h hydrothermal reaction at 180 °C and subsequent calcination, well-crystallized Li4Ti5O12–BN nanoplates were produced, which demonstrate a superior discharge capacity of 160 mA h g−1, even at 40 C, maintaining a capacity of 88.8% compared with that at 1 C. The nanoplates also exhibited excellent cycling stability, retaining a discharge capacity of 153 mA h g−1 after 1000 charge–discharge cycles at 10 C.

We demonstrate a facile and effective way for the fabrication of a flexible, homogeneous and neat α-MoO3 thin-film electrode for lithium-ion batteries with high performance without using any binder and conductive additives. Single-crystalline α-MoO3 nanobelts with uniform width of around 200 nm and length at the micrometer level are first synthesized by a simple water-based hydrothermal route. The as-obtained α-MoO3 slurry is then directly deposited onto a copper foil current collector by the doctor blade method. The formation of the α-MoO3 film and its good adhesion to the current collector is realized via van der Waals attraction forces through a drying process. The structure and morphology of the α-MoO3 nanobelt particles and thin-film electrode are systematically characterized by XRD, Raman spectra, TEM, SEM and XPS techniques, and the electrochemical properties are investigated by CV and constant current discharge–charge test techniques. The α-MoO3 film electrode exhibits a reversible specific capacity of ∼1000 mA h g−1 at 50 mA g−1 and a stable capacity retention of 387–443 mA h g−1 at 2000 mA g−1, indicating its high Li storage capacity, superior rate performance and good cycling stability. The electrode material, as well as the fabrication technique, is highly promising for practical use in high energy and power density lithium-ion batteries.

Cobalt-free perovskite BaNb0.05Fe0.95O3−δ (BNF) is synthesized and characterized towards application as a cathode material for intermediate temperature solid oxide fuel cells. In situ X-ray diffraction and transmission electron microscopy are applied to study the crystal structure and thermally induced phase transformation. BNF exists as a multiphase structure composed of a monoclinic phase and a cubic phase at room temperature, and then undergoes a phase transformation to a cubic structure starting at ∼400 °C, which is maintained at temperatures up to 900 °C during a thermal cycle between room temperature and 900 °C; while it retains the cubic perovskite lattice structure on cooling from 900 °C to room temperature. Oxygen temperature-programmed desorption, combined thermal expansion and thermo-gravimetric analysis are used to clarify the thermal reducibility of BNF. A relatively good stability of BNF is demonstrated by electrical conductivity and electrochemical impedance spectroscopy measurements. The activity of BNF for oxygen reduction reaction is probed by symmetrical cell and single fuel cell tests. Favorable electrochemical activities at intermediate temperature, e.g. very low interfacial resistance of only ∼0.016 Ω cm2 and maximum power density of 1162 mW cm−2 at 750 °C, are demonstrated, which could be attributed to the cubic lattice structure of BNF within the temperature range of cell operation.