HF free greener Cl ‐terminated MXene as novel electrocatalyst for overall water splitting in alkaline media

Abstract

Summary Hydrogen and oxygen evolution through electrochemical water splitting is essential for effective and inexpensive production of hydrogen and oxygen, which depends on the development of economical, and extremely active electrocatalysts. Two‐dimensional (2D) nano‐laminated materials are imperious as electrocatalysts due to their phenomenal properties and extensive scope of applications. In this work, we report a greener way of synthesizing MXene without hydrofluoric acid (HF) treatment and demonstrated its excellent electrochemical characteristics as an overall water‐splitting catalyst. Cl‐terminated MXenes (Ti3C2Cl2) were synthesized via a molten salt approach, in which the MAX phase (Ti3AlC2) was reacted with copper chloride (CuCl2) salt followed by thermal treatment at a temperature of 550°C for 5 hours. The resulting Cl‐terminated MXene was characterized by scanning electron microscopy, X‐ray diffraction, transmission electron microscope, Raman, Fourier transform infrared spectroscopy, energy dispersive X‐ray analysis, X‐ray photoelectron spectroscopy, and electrochemical testing was performed in the alkaline media for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). For OER in 1 M KOH, Cl‐terminated MXene achieves a benchmark of 30 mA cm−2 current density at an overpotential of 330 mV and a Tafel slope of 48 mV dec−1, while HF‐MXene exhibits an overpotential of 390 mV and a Tafel slope of 136 mV dec−1. For HER, Cl‐MXene attains an overpotential of 259 mV, and a Tafel slope of 92 mV dec−1 to achieve the 10 mA cm−2 current density, on the other hand, HF‐MXene achieves an overpotential of 444 mV and a Tafel slope of 311 mV dec−1. Furthermore, the electrocatalyst exhibited excellent long‐term stability of 0.7 V at 100 mA cm−2 current density for 36 hours. The synthesis methodology for greener Cl‐terminated MXene coupled with an outstanding electrocatalytic activity is set to open new avenues of catalyst design for water splitting.

Recent Advances and Perspectives of Lewis Acidic Etching Route: An Emerging Preparation Strategy for MXenes

“…Exploring high-performance electrocatalysts can effectively solve the above-mentioned issues. For example, Sarfraz et al reported the synthesis of Clterminated Ti 3 C 2 Cl 2 MXene via CuCl 2 etching of Ti 3 AlC 2 precursor in 2022, and Ti 3 C 2 Cl 2 MXene with obvious lamellar structure is then used as catalyst for water splitting in 1 M KOH solution [237]. Compared with Ti 3 C 2 T x MXene obtained by HF etching (HF-Ti 3 C 2 T x MXene), Ti 3 C 2 Cl 2 MXene possesses an enlarged interlayer spacing, more active sites and stable architecture.…”

Retrospective insights into recent MXene-based catalysts for CO2electro/photoreduction: how far have we gone?

“…Similarly, a greener synthesis route was also developed by Sarfraz et al , in which a Cl-terminated MXene was synthesized from the Ti 3 AlC 2 MAX phase via thermally reacting with a CuCl 2 salt at a high temperature in an inert environment, to successfully get rid of the HF. 100…”

“…Similarly, a greener synthesis route was also developed by Sarfraz et al, in which a Cl-terminated MXene was synthesized from the Ti 3 AlC 2 MAX phase via thermally reacting with a CuCl 2 salt at a high temperature in an inert environment, to successfully get rid of the HF. 100 Importantly, etching conditions, including the HF concentration, etching temperature, and etching time, significantly influence the formation and properties of MXenes by adjusting the defects and surface terminations. 101,102 For example, a higher HF concentration (direct 48% HF etching) resulted in more -F surface terminations when compared with the amount of -O or -OH termination on Ti 3 AlC 2 , while a lower HF concentration (in situ HF-forming) produced Ti 3 AlC 2 with more -O terminations (Fig.…”

A Review on MXene as Promising Support Materials for Oxygen Evolution Reaction Catalysts

“…[32][33][34][35][36][37] Transition metal carbides or nitrides or carbonitrides of two-dimensional (2D) materials, also known as MXene (M n+1 X n T x (n = 1, 2, 3), M = early transition metal, X = carbon and/or nitrogen, and T x = surface functional groups, such as ─O, ─OH, or ─F), are emerging as new candidates for catalyst supports owing to their unique properties such as high electrical conductivity, hydrophilicity, abundant surface functional groups, and stability. [38][39][40][41] Although MXene has recently been studied as an electrocatalyst for clean energy conversion reactions, [31,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] its practical use is rarely feasible due to the large gap in reaching the catalytic activity levels of the related technologies. Meanwhile, many studies have obtained promising results when using MXene as the support material, including for OER catalysts.…”