Reversing Interfacial Catalysis of Ambipolar WSe₂ Single Crystal

Abstract

An improved understanding of the origin of the electrocatalytic activity is of importance to the rational design of highly efficient electrocatalysts for the hydrogen evolution reaction. Here, an ambipolar single‐crystal tungsten diselenide (WSe2) semiconductor is employed as a model system where the conductance and carrier of WSe2 can be individually tuned by external electric fields. The field‐tuned electrochemical microcell is fabricated based on the single‐crystal WSe2 and the catalytic activity of the WSe2 microcell is measured versus the external electric field. Results show that WSe2 with electrons serving as the dominant carrier yields much higher activity than WSe2 with holes serving as the dominant carrier even both systems exhibit similar conductance. The catalytic activity enhancement can be characterized by the Tafel slope decrease from 138 to 104 mV per decade, while the electron area concentration increases from 0.64 × 1012 to 1.72 × 1012 cm−2. To further understand the underlying mechanism, the Gibbs free energy and charge distribution for adsorbed hydrogen on WSe2 versus the area charge concentration is systematically computed, which is in line with experiments. This comprehensive study not only sheds light on the mechanism underlying the electrocatalysis processes, but also offers a strategy to achieve higher electrocatalytic activity.

Non‐Noble‐Metal‐Based Electrocatalysts toward the Oxygen Evolution Reaction

“…Bimetallic NiFe phosphosulfide nanocomposite also exhibits appreciable overall water splitting performance with a low cell voltage of 1.58 V to achieve the current density of 10 mA cm –2 113. Moreover, nanoengineering active edge sites and interfacial catalysis are effective strategies to enhance the intrinsic activity of catalytic materials, as proven in both OER and HER 114–116. Introducing more edges and corner sites helps decrease the coordination number of the surface reactive sites and affects the electronic structure of catalysts, which in turn boost the electrocatalytic performance 114,116.…”

pH, Nanosheet Concentration, and Antioxidant Affect the Oxidation of Ti3C2Tx and Ti2CTx MXene Dispersions

“…MXenes are a family of transition metal carbides, carbonitrides, and nitrides with layered 2D nanostructures and have a general formula M n +1 X n T x , where M represents an early transition metal element such as titanium (Ti), vanadium (V), and niobium (Nb), X is carbon and/or nitrogen, T refers to one or multiple terminal groups (OH, O, F), n usually ranges from 1 to 3, and x reflects the number of terminal groups. [ 1–5 ] MXenes have drawn much attention for their potential use in energy storage, [ 1,6 ] sensing technology, [ 7,8 ] functional coatings, [ 9–11 ] plasmonics, [ 12 ] and catalytic applications [ 13–15 ] due to their high electrical conductivity, hydrophilicity, and surface charge. Most of those properties can be traced back to their metallic‐like 2D structure and functional groups attached during the etching and delamination processes.…”

Enhanced Ionic Accessibility of Flexible MXene Electrodes Produced by Natural Sedimentation

“…However, the electrochemical properties of those materials need further improvement. Transition metal carbides, nitrides and carbonitrides, a large family of two-dimensional (2D) materials known as MXenes, have been gaining a lot of interest in a variety of applications, especially for energy storage and conversion [8][9][10]. The characteristics of MXenes, including their unique 2D morphologies, rich chemistries, ultra-high electronic conductivities, and abundant surface functional groups, make them promising candidates for electrodes of supercapacitors (SCs) and LIBs [11][12][13][14][15].…”