Tuning the Electrochemical Performance of Titanium Carbide MXene by Controllable In Situ Anodic Oxidation

MXenes are a class of two‐dimensional (2D) transition metal carbides, nitrides and carbonitrides that have shown promise for high‐rate pseudocapacitive energy storage. However, the effects that irreversible oxidation have on the surface chemistry and electrochemical properties of MXenes are still not understood. Here we report on a controlled anodic oxidation method which improves the rate performance of titanium carbide MXene (Ti₃C₂T_x, T_x refers to ‐F, =O, ‐Cl and ‐OH) electrodes in acidic electrolytes. The capacitance retention at 2000 mV s^?1 (with respect to the lowest scan rate of 5 mV s^?1) increases gradually from 38 % to 66 % by tuning the degree of anodic oxidation. At the same time, a loss in the redox behavior of Ti₃C₂T_x is evident at high anodic potentials after oxidation. Several analysis methods are employed to reveal changes in the structure and surface chemistry while simultaneously introducing defects, without compromising electrochemically active sites, are key factors for improving the rate performance of Ti₃C₂T_x. This study demonstrates improvement of the electrochemical performance of MXene electrodes by performing a controlled anodic oxidation.     

Potassium‐Ion‐Assisted Regeneration of Active Cyano Groups in Carbon Nitride Nanoribbons: Visible‐Light‐Driven Photocatalytic Nitrogen Reduction

As a metal‐free nitrogen reduction reaction (NRR) photocatalyst, g‐C₃N₄ is available from a scalable synthesis at low cost. Importantly, it can be readily functionalized to enhance photocatalytic activities. However, the use of g‐C₃N₄‐based photocatalysts for the NRR has been questioned because of the elusive mechanism and the involvement of N defects. This work reports the synthesis of a g‐C₃N₄ photocatalyst modified with cyano groups and intercalated K⁺ (mCNN), possessing extended visible‐light harvesting capacity and superior photocatalytic NRR activity (NH₃ yield: 3.42 mmol g^?1 h^?1). Experimental and theoretical studies suggest that the ‐C≡N in mCNN can be regenerated through a pathway analogous to Mars van Krevelen process with the aid of the intercalated K⁺. The results confirm that the regeneration of the cyano group not only enhances photocatalytic activity and sustains the catalytic cycle, but also stabilizes the photocatalyst.     

C−H Arylation on Nickel Nanoparticles Monitored by In Situ Surface‐Enhanced Raman Spectroscopy

Bifunctional Au@Ni core–satellite nanostructures synthesized by a one‐step assembly method were employed for in situ surface‐enhanced Raman spectroscopic (SERS) monitoring of Ni‐catalyzed C?C bond‐forming reactions. Surprisingly, the reaction that was thought to be an Ullmann‐type self‐coupling reaction, was found to be a cross‐coupling reaction proceeding by photoinduced aromatic C?H bond arylation. In situ SERS monitoring enabled the discovery, and a series of biphenyl compounds were synthesized photocatalytically, and at room temperature, using cheap Ni nanoparticle catalysts.     

Chelating N‐Heterocyclic Carbene Ligands Enable Tuning of Electrocatalytic CO2 Reduction to Formate and Carbon Monoxide: Surface Organometallic Chemistry

Reported here is the chelate effect as a design principle for tuning heterogeneous catalysts for electrochemical CO₂ reduction. Palladium functionalized with a chelating tris‐N‐heterocyclic carbene (NHC) ligand (Pd‐timtmb^Me) exhibits a 32‐fold increase in activity for electrochemical reduction of CO₂ to C1 products with high Faradaic efficiency (FE_C1=86 %) compared to the parent unfunctionalized Pd foil (FE=23 %), and with sustained activity relative to a monodentate NHC‐ligated Pd electrode (Pd‐mimtmb^Me). The results highlight the contributions of the chelate effect for tailoring and maintaining reactivity at molecular‐materials interfaces enabled by surface organometallic chemistry.