Ultrathin Metal Silicate Hydroxide Nanosheets with Moderate Metal-Oxygen Covalency Enables Efficient Oxygen Evolution

Exploring efficient,cost-effective,and durable electrocatalysts for electrochemical oxygen evolution reaction(OER)is pivotal for the large-scale application of water electrolysis.Recent advance has demonstrated that the activity of electrocatalysts exhibits a strong dependence on the surface electronic structure.Herein,a series of ultrathin metal silicate hydroxide nanosheets(UMSHNs)M_(3)Si_(2)O_(5)(OH)_(4)(M=Fe,Co,and Ni)synthesized without surfactant are introduced as highly active OER electrocatalysts.Cobalt silicate hydroxide nanosheets show an optimal OER activity with overpotentials of 287 and 358 m V at 1 and 10 m A cm^(-2),respectively.Combining experimental and theoretical studies,it is found that the OER activity of UMSHNs is dominated by the metal-oxygen covalency(MOC).High OER activity can be achieved by having a moderate MOC as reflected by aσ^(*)-orbital(e_(g))filling near unity and moderate[3d]/[2p]ratio.Moreover,the UMSHNs exhibit favorable chemical stability under oxidation potential.This contribution provides a scientific guidance for further development of active metal silicate hydroxide catalysts.

Fabricating ion-conducting channel in SU-8 matrix for highperformance patternable polymer electrolytes

Advances in electrochemical energy storage technologies drive the need for battery safety performance and miniaturization,which calls for the easily processable polymer electrolytes suitable for on-chip microbattery technology.However,the low ionic conductivity of polymer electrolytes and poor-patternable capabilities hinder their application in microdevices.Herein,we modified SU-8,as the matrix material,by poly(ethylene oxide)(PEO)with lithium salts to obtain a patternable lithium-ion polymer electrolyte.Due to the highly amorphous state and more Li-ion transport pathways through blending effect and the increase in number of epoxides,the ionic conductivity of achieved sample is increased by an order of magnitude to 2.9×10^(−4) S·cm^(−1) in comparison with the SU-8 sample at 50°C.The modified SU-8 exhibits good thermal stability(>150°C),mechanical properties(elastic modulus of 1.52 GPa),as well as an electrochemical window of 4.3 V.Half-cell and microdevice were fabricated and tested to verify the possibility of the micro-sized on-chip battery.All of these results demonstrate a promising strategy for the integration of on-chip batteries with microelectronics.

Electric field and photoelectrical effect bi-enhanced hydrogen evolution reaction

Molybdenum disulfide （MoS2） is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced after modification due to higher conductivity and enriched active sites. However, the underlying mechanism of the influence of the resistance of electrode material and contact resistance on the hydrogen evolution reaction （HER） process is unclear. Herein, we present a systematic study to understand the relationship between HER performance and electrode conductivity, which is bi-tuned through the electric field and photoelectrical effect. It was found that the onset overpotential consistently decreased with the increase of electrode conductivity. In addition, the reduction of the contact resistance resulted in a quicker electrochemical reaction process than enhancing the conductivity of the MoS2 nanosheet. An onset overpotential of 89 mV was achieved under 60 mW/cm^2 sunlight illumination （0.6 sun） and a simultaneous gate voltage of 3 V. These physical strategies can also be applied to other catalysts, and offer new directions to improve HER catalytic performance of semiconductor materials.

Illumining phase transformation dynamics of vanadium oxide cathode by multimodal techniques under operando conditions

Subtle structural changes during electrochemical processes often relate to the degradation of electrode materials.Characterizing the minute-variations in complementary aspects such as crystal structure,chemical bonds,and electron/ion conductivity will give an in-depth understanding on the reaction mechanism of electrode materials,as well as revealing pathways for optimization.Here,vanadium pentoxide (V2O5),a typical cathode material suffering from severe capacity decay during cycling,is characterized by in-situ X-ray diffraction (XRD) and in-situ Raman spectroscopy combined with electrochemical tests.The phase transitions of V2O5 within the 0-1 LiN ratio are characterized in detail.The V--O and V-V distances became more extended and shrank compared to the original ones after charge/discharge process,respectively.Combined with electrochemical tests,these variations are vital to the crystal structure cracking,which is linked with capacity fading.This work demonstrates that chemical bond changes between the transition metal and oxygen upon cycling serve as the origin of the capacity fading.