Modification of spinel MnCo2O4 nanowire with NiFe-layered double hydroxide nanoflakes for stable seawater oxidation.

Currently, direct electrolysis of seawater-based electrolytes rather than fresh water based ones for hydrogen production is gaining more and more attentions for creating a sustainable society. However, using seawater remains more challenges owing to the existence of competitive reactions between chlorine evolution reaction (ClER) or hypochlorite generation reaction and oxygen evolution reaction (OER) and electrode erosion. In this study, a MnCo2O4 nanowire coated with NiFe-Layered Double Hydroxide (NiFe-LDH) layer (MnCo2O4@NiFe-LDH) composite electrocatalyst prepared by a simple two-step hydrothermal method was applied for the seawater electrolysis, which exhibited low overpotentials of 219 and 245 mV at a relatively high current density of 100 mA cm-2 in alkaline simulated and natural seawaters, respectively, as the anode electrocatalyst. It is found that the NiFe-LDH layer on the MnCo2O4 nanowire can serve as Cl- protective layer to hinder the ClER and anode erosion and simultaneously improve the active surface area and intrinsic properties of MnCo2O4 nanowires, allowing for faster kinetics. While, the high valence states of Mn3+, Co3+, Ni3+and Fe3+ played a vital role for OER. In addition, when it was used as the bifunctional electrocatalyst for the overall real seawater splitting, the cell composed of MnCo2O4@NiFe-LDH (-) || MnCo2O4@NiFe-LDH (+) pair only required a low voltage of 1.56 V@10 mA cm-2 and simultaneously maintained excellent stability at a high current density of 100 mA cm-2. Such an electrocatalyst could be a promising candidate for long-term seawater splitting.

A poly(ether block amide) based solid polymer electrolyte for solid-state lithium metal batteries.

Solid-state lithium (Li) metal batteries (SSLMBs) with high-energy density and high-security are promising for energy storage application and electronic device development. However, Li dendrite generation is still one of the most important factors hindering the application of SSLMBs since interface contact degradation, dead Li accumulation, and continuous solid-electrolyte interphase (SEI) growth are always caused by Li dendrite growth, making the performances of SSLMBs deteriorate rapidly. In this study, a poly(ether block amide) (PEBA) based polymer electrolyte with lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI) as the Li salt is developed. It is found that the PEBA 2533-20% LiTFSI electrolyte possesses an ion conductivity of 3.0 × 10-5 S cm-1 at 25 °C. Especially, the Li dendrite suppression ability of SEI is greatly enhanced since it provides abundant amide groups to activate TFSI- anions and further enriches lithium fluoride (LiF) content in the SEI layer, which endows the full-cell with enhanced cyclability. As a result, the fabricated solid-state Li/PEBA 2533-20% LiTFSI/LiFePO4 (areal capacity: 0.15 mAh cm-2) battery remains 94% of its maximum capacity (127.5 mAh g-1) at a rate of 0.5C and 60 °C after 200 cycles. In particular, the full cell can cycle for almost 1000 times without short circuit. Therefore, the PEBA based electrolyte could promote the LiF enriched SEI layer into a platform to suppress the growth of Li dendrite toward SSLMBs with a long-life span.

Fabrication of a High-Energy Flexible All-Solid-State Supercapacitor Using Pseudocapacitive 2D-Ti3C2Tx-MXene and Battery-Type Reduced Graphene Oxide/Nickel-Cobalt Bimetal Oxide Electrode Materials.

Owing to excellent metallic conductivity, hydrophilic surfaces, and surface redox properties, a two-dimensional (2D) metal carbide of Ti3C2Tx-MXene could serve as a promising pseudocapacitive electrode material for energy storage devices. Meanwhile, the 2D reduced graphene oxide (rGO) combining with the hierarchical cubic spinel nickel-cobalt bimetal oxide (NiCo2O4) nanospikes could control ion diffusion for charge storage, thereby facilitating the improvement of the energy density of a supercapacitor. As per the strategy, the pseudocapacitive 2D Ti3C2Tx was loaded on a flexible acid-treated carbon fiber (ACF) backbone to prepare a Ti3C2Tx/ACF negative electrode by a convenient drop-casting method. Meanwhile, 2D rGO was deposited on ACF by a simple dip-dry process, which was further decorated by the spinel NiCo2O4 nanospikes using a hydrothermal method to obtain a NiCo2O4@rGO/ACF positive electrode. The fabricated Ti3C2Tx/ACF electrode exhibited an excellent specific capacitance of 246.9 F/g (197.5 mF/cm2) at 4 mA/cm2 along with 96.7% capacity retention over 5000 charge/discharge cycles, whereas the NiCo2O4@rGO/ACF electrode showed a specific capacitance of 1487 F/g (458.3 mA h/g) at 3 mA/cm2 with a cycling stability of 88.2% over 10 000 charge/discharge cycles. As a result, a flexible all-solid-state hybrid supercapacitor (FHSC) device using the pseudocapacitive Ti3C2Tx/ACF on the negative side with a widespread voltage window and the battery-type NiCo2O4@rGO/ACF on the positive side with high electrochemical activity delivered an excellent volumetric capacitance of 2.32 F/cm3 (141.9 F/g) at a current density of 5 mA/cm2 with a high-energy density of 44.36 Wh/kg (0.72 mWh/cm3) at a power density of 985 W/kg (16.13 mW/cm3) along with a cycling stability of 90.48% over 4500 charge/discharge cycles. Therefore, the pseudocapacitive 2D Ti3C2Tx/ACF negative electrode could replace carbon-based electrodes and a combination of it with the battery-type NiCo2O4@rGO/ACF positive electrode should be a promising way to step up the energy density of a supercapacitor.