Tuning the Basal Plane Functionalization of Two-Dimensional Metal Carbides (MXenes) To Control Hydrogen Evolution Activity

Abstract

Hydrogen evolution reaction (HER) via electrocatalysis is one method of enabling sustainable production of molecular hydrogen as a clean and promising energy carrier. Previous theoretical and experimental results have shown that some two-dimensional (2D) transition metal carbides (MXenes) can be effective electrocatalysts for the HER, based on the assumption that they are functionalized entirely with oxygen or hydroxyl groups on the basal plane. However, it is known that MXenes can contain other basal plane functionalities, e.g., fluorine, due to the synthesis process, yet the influence of fluorine termination on their HER activity remains unexplored. In this paper, we investigate the role and effect of basal plane functionalization (T x ) on the HER activity of 5 different MXenes using a combination of experimental and theoretical approaches. We first studied Ti 3 C 2 T x produced by different fluorinecontaining etchants and found that those with higher fluorine coverage on the basal plane exhibited lower HER activity. We then controllably prepared Mo 2 CT x with very low basal plane fluorine coverage, achieving a geometric current density of −10 mA cm −2 at 189 mV overpotential in acid. More importantly, our results indicate that the oxygen groups on the basal planes of Mo 2 CT x are catalytically active toward the HER, unlike in the case of widely studied 2H-phase transition metal dichalcogenides such as MoS 2 , in which only the edge sites are active. These results pave the way for the rational design of 2D materials for either the HER, when minimal overpotential is desired, or for energy storage, when maximum voltage window is needed.

Oxygen‐Functionalized Ultrathin Ti3C2Tx MXene for Enhanced Electrocatalytic Hydrogen Evolution

“…Handoko et al. demonstrated that a higher F coverage on the basal plane of Ti 3 C 2 , Mo 2 C, and Mo 2 Ti 2 C 3 MXenes resulted in a lower HER activity . Ran et al.…”

“…[26][27][28][29] Handoko et al demonstrated that a higherFcoverage on the basal plane of Ti 3 C 2 ,M o 2 C, and Mo 2 Ti 2 C 3 MXenes resulted in al ower HER activity. [30] Ran et al calculated the Gibbs free energy for hydrogen adsorption (DG H* )o nT i 3 C 2 with different terminal groups (ÀFa nd ÀO) by density functional theory( DFT). It was observed that O-terminated Ti 3 C 2 showed an ear-zero value of j (DG H* j = 0.00283 eV at its optimal H* coverage (q = 1/2), even lower than that of Pt (DG H* = À0.009 eV).…”

Synthesis and photocatalytic H2‐production activity of plasma‐treated Ti3C2Tx MXene modified graphitic carbon nitride

“…[27][28][29] In recent years, Handoko et al theoretically demonstrated that benefiting from their (the 2D MXenes) high electrical conductivity and layered structure, photo-generated electron-hole pairs can quickly be transferred. [30][31][32] In particular, the numerous hydrophilic functional groups on Ti 3 C 2 T x (T = OH/F/O) MXene promote its strong interaction with water molecules. Thus, Ti 3 C 2 T x MXene has been regarded as a good co-catalyst in photocatalysis reaction.…”

Self‐Assembly of Large‐Area 2D Polycrystalline Transition Metal Carbides for Hydrogen Electrocatalysis

“…The material performance can be attributed to several key properties, including high surface area due to the ultrathin structure, robust conjugation between Mo 2 C and the rich carbon phase for high conductivity and electron transport, abundant grain boundaries that could perform as active center originating from nanocrystals, and the catalytic activity of the material lattice plane. Catalyst efficacy is particularly dependent on the lattice plane; for example, the activities of basal and edge of chalcogenides and MXenes widely differ . As a general rule, large single crystals or sheets have their lowest‐energy surface exposed, and have a corresponding poor catalytic performance.…”