Yuxiang Hu

An Electrochemically Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting

BiVO4 films with (040) facet grown vertically on fluorine doped SnO2 (FTO) glass substrates are prepared by a seed-assisted hydrothermal method. A simple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO4 , exhibiting a remarkable photocurrent density of 2.5 mA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is approximately 10-fold higher than that of the pristine photoanode. Loading cobalt borate (CoBi) as cocatalyst, the photocurrent density of the BiVO4 photoanode can be further improved to 3.2 mA cm-2 , delivering an applied bias photon-to-current efficiency (ABPE) of 1.1 %. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies, resulting in remarkably enhanced photocurrent densities. These findings provide a facile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.

Carbon-Coated Na3.32Fe2.34(P2O7)2 Cathode Material for High-Rate and Long-Life Sodium-Ion Batteries

Rechargeable sodium-ion batteries are proposed as the most appropriate alternative to lithium batteries due to the fast consumption of the limited lithium resources. Due to their improved safety, polyanion framework compounds have recently gained attention as potential candidates. With the earth-abundant element Fe being the redox center, the uniform carbon-coated Na3.32 Fe2.34 (P2 O7 )2 /C composite represents a promising alternative for sodium-ion batteries. The electrochemical results show that the as-prepared Na3.32 Fe2.34 (P2 O7 )2 /C composite can deliver capacity of ≈100 mA h g-1 at 0.1 C (1 C = 120 mA g-1 ), with capacity retention of 92.3% at 0.5 C after 300 cycles. After adding fluoroethylene carbonate additive to the electrolyte, 89.6% of the initial capacity is maintained, even after 1100 cycles at 5 C. The electrochemical mechanism is systematically investigated via both in situ synchrotron X-ray diffraction and density functional theory calculations. The results show that the sodiation and desodiation are single-phase-transition processes with two 1D sodium paths, which facilitates fast ionic diffusion. A small volume change, nearly 100% first-cycle Coulombic efficiency, and a pseudocapacitance contribution are also demonstrated. This research indicates that this new compound could be a potential competitor for other iron-based cathode electrodes for application in large-scale Na rechargeable batteries.

An Innovative Freeze-Dried Reduced Graphene Oxide Supported SnS2 Cathode Active Material for Aluminum-Ion Batteries

Rechargeable aluminum-ion batteries (AIBs) are attractive new generation energy storage devices due to its low cost, high specific capacity, and good safety. However, the lack of suitable electrode materials with high capacity and enhanced rate performance makes it difficult for real applications. Herein, the preparation of 3D reduced graphene oxide-supported SnS2 nanosheets hybrid is reported as a new type of cathode material for AIBs. The resultant material demonstrates one of the highest capacities of 392 mAh g-1 at 100 mA g-1 and good cycling stability. It is revealed that the layered SnS2 nanosheets anchored on 3D reduced graphene oxide network endows the composite not only high electronic conductivity but also fast kinetic diffusion pathway. As a result, the hybrid material exhibits high rate performance (112 mAh g-1 at 1000 mA g-1 ). The detailed characterization also verifies the intercalation and deintercalation of relatively large chloroaluminate anions into the layered SnS2 during the charge-discharge process, which is important for better understanding of the electrochemical process of AIBs.

Cobalt nanoparticles encapsulated in carbon nanotube-grafted nitrogen and sulfur co-doped multichannel carbon fibers as efficient bifunctional oxygen electrocatalysts

Developing flexible, efficient, and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is of paramount importance for designing fuel cells, metal–air batteries and water splitting units. Herein we present an economical approach for the synthesis of self-standing cobalt nanoparticles (NPs) anchored on carbon nanotube-grafted multichannel carbon fibers, co-doped with nitrogen and sulfur (Co@NS/CNT-MCFs), which exhibit comparable ORR (OER) activity to that of commercial Pt/C (RuO2) catalysts in terms of a half-wave potential of 0.837 V for the ORR, and a mere 362 mV overpotential at a current density of 10 mA cm−2 for the OER, as well as remarkable stability in an alkaline medium. The excellent electrocatalytic properties can be attributed to the hierarchically porous network structure and multiple heteroatom dopants introduced, which favor efficient reagent/product mass transport, in addition to providing a great number of active sites. As a proof of concept, the designed flexible catalysts are also employed as air cathodes in an assembled lithium–oxygen (Li–O2) cell with high specific capacity and outstanding operational durability. These results demonstrate the potential of this novel approach in developing suitable catalysts to enable the next generation of metal–air batteries.

A Binder‐Free and Free‐Standing Cobalt Sulfide@Carbon Nanotube Cathode Material for Aluminum‐Ion Batteries

Rechargeable aluminum-ion batteries (AIBs) are considered as a new generation of large-scale energy-storage devices due to their attractive features of abundant aluminum source, high specific capacity, and high energy density. However, AIBs suffer from a lack of suitable cathode materials with desirable capacity and long-term stability, which severely restricts the practical application of AIBs. Herein, a binder-free and self-standing cobalt sulfide encapsulated in carbon nanotubes is reported as a novel cathode material for AIBs. The resultant new electrode material exhibits not only high discharge capacity (315 mA h g-1 at 100 mA g-1 ) and enhanced rate performance (154 mA h g-1 at 1 A g-1 ), but also extraordinary cycling stability (maintains 87 mA h g-1 after 6000 cycles at 1 A g-1 ). The free-standing feature of the electrode also effectively suppresses the side reactions and material disintegrations in AIBs. The new findings reported here highlight the possibility for designing high-performance cathode materials for scalable and flexible AIBs.

The impact of the molecular weight on the electrochemical properties of poly(TEMPO methacrylate)

Synthesis of TEMPO-containing polymers by ‘living’ radical polymerization provides opportunities to investigate the impact of the molecular weight on their electrochemical properties. In this work, we utilized single electron transfer-living radical polymerization (SET-LRP) to synthesize poly(2,2,6,6-tetramethylpiperidine methacrylate) (PTMPM) with degrees of polymerization ranging from 66 to 703, and after oxidation producing poly(TEMPO methacrylate) (PTMA) with the highest molecular weight of 169 kDa and dispersity of 1.35. Three different techniques were used to quantify the radical density and calculate the theoretical capacity of PTMA polymers. These PTMA polymers, as active materials with 25 wt% in the electrode composite, showed strong molecular weight dependence on the electrochemical properties. The higher molecular weight PTMA polymers showed higher specific discharging capacities and better cycling stability due to their lower solubility in the electrolyte.

A new sodium iron phosphate as a stable high-rate cathode material for sodium ion batteries

Low-cost room-temperature sodium-ion batteries (SIBs) are expected to promote the development of stationary energy storage applications. However, due to the large size of Na+, most Na+ host structures resembling their Li+ counterparts show sluggish ion mobility and destructive volume changes during Na ion (de)intercalation, resulting in unsatisfactory rate and cycling performances. Herein, we report a new type of sodium iron phosphate (Na0.71Fe1.07PO4), which exhibits an extremely small volume change (~ 1%) during desodiation. When applied as a cathode material for SIBs, this new phosphate delivers a capacity of 78 mA·h·g−1 even at a high rate of 50 C and maintains its capacity over 5,000 cycles at 20 C. In situ synchrotron characterization disclosed a highly reversible solid-solution mechanism during charging/discharging. The findings are believed to contribute to the development of high-performance batteries based on Earth-abundant elements.