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Abstract Electrochemical applications of metal organic frameworks (MOFs) are of considerable current interest. Due to the large surface area exposed to solution, MOFs are potentially useful electrode materials for sensing inner‐sphere analytes, such as reactive oxygen species. Herein, we electrodeposited copper benzene tricarboxylate MOF (HKUST‐1) into the cavity of an open carbon nanopipette (CNP) to produce a CNP‐MOF nanoelectrode. Unlike electronically conductive metal or carbon electrodes, the electrochemical response of CNP–MOFs relies on oxidation/reduction of Cu(I)/Cu(II) nodes in the porous nanostructure. Nevertheless, sigmoidal steady‐state voltammograms with a well‐defined plateau current have been recorded for simple redox mediators, for example, ferrocenemethanol. A linear calibration curve obtained for the hydrogen peroxide reduction suggests that CNP–MOFs can potentially be useful as nanosensors for peroxide. 

Abstract 2D early transition metal carbide and nitride MXenes have intriguing properties for electrochemical energy storage and electrocatalysis. These properties can be manipulated by modifying the basal plane chemistry. Here, mixed transition metal nitride MXenes, M‐Ti₄N₃T_x(M = V, Cr, Mo, or Mn; T_x= O and/or OH), are developed by modifying pristine exfoliated Ti₄N₃T_xMXene with V, Cr, Mo, and Mn salts using a simple solution‐based method. The resulting mixed transition metal nitride MXenes contain 6–51% metal loading (cf. Ti) that exhibit rich electrochemistry including highly tunable hydrogen evolution reaction (HER) electrocatalytic activity in a 0.5mH₂SO₄electrolyte as follows: V‐Ti₄N₃T_x> Cr‐Ti₄N₃T_x> Mo‐Ti₄N₃T_x> Mn‐Ti₄N₃T_x> pristine Ti₄N₃T_xwith overpotentials as low as 330 mV at −10 mA cm⁻²with a charge‐transfer resistance of 70 Ω. Scanning electrochemical microscopy (SECM) reveals the electrochemical activity of individual MXene flakes. The SECM data corroborate the bulk HER activity trend for M‐Ti₄N₃T_xas well as provide the first experimental evidence that HER results from catalysis on the MXene basal plane. These electrocatalytic results demonstrate a new pathway to tune the electrochemical properties of MXenes for water splitting and related electrochemical applications.