True Nature of the Transition-Metal Carbide/Liquid Interface Determines Its Reactivity

Abstract

Compound materials, such as transition-metal (TM) carbides, are anticipated to be effective electrocatalysts for the carbon dioxide reduction reaction (CO 2 RR) to useful chemicals. This expectation is nurtured by density functional theory (DFT) predictions of a break of key adsorption energy scaling relations that limit CO 2 RR at parent TMs. Here, we evaluate these prospects for hexagonal Mo 2 C in aqueous electrolytes in a multimethod experiment and theory approach. We find that surface oxide formation completely suppresses the CO 2 activation. The oxides are stable down to potentials as low as −1.9 V versus the standard hydrogen electrode, and solely the hydrogen evolution reaction (HER) is found to be active. This generally points to the absolute imperative of recognizing the true interface establishing under operando conditions in computational screening of catalyst materials. When protected from ambient air and used in nonaqueous electrolyte, Mo 2 C indeed shows CO 2 RR activity.

Epitaxial Core‐Shell Oxide Nanoparticles: First‐Principles Evidence for Increased Activity and Stability of Rutile Catalysts for Acidic Oxygen Evolution

“…This descriptor neither accounts for the chemical properties of the decomposition products nor for mass transport effects as has been pointed out recently [39] . Such influences can be treated approximately by simple models based on the Poisson‐Nernst‐Planck equations which, to lowest order, will induce shifts in the phase diagrams [45] . For the highly similar systems considered here, we assume that these shifts are approximately constant over the range of systems studied and that our current approach delivers an acceptable semi‐quantitative estimate of which structural modifications might improve the relative stability of the catalyst within its class.…”

Formic acid reduction and CO2 activation at Mo2C: The important role of surface oxide

“…They consist of large, several micrometer wide, smooth, and chemically homogeneous terraces and the Mo 2 C is characterized by a hexagonal structure. [ 29 ]…”

“…[ 11 ] The observed difference might originate from the chemical nature of the compound material Mo 2 C that is covered with an ultrathin oxide layer in the studied potential range. [ 29 ] This can influence the solid/liquid interface in general, and the adsorption properties of intermediates in particular, in a different way than the bare metals previously studied, and determines its formic acid reduction activity.…”

“…We report on the electro‐reduction of formic acid on planar hexagonal Mo 2 C films, synthesized from polycrystalline Mo electrodes as shown in ref. [29], in 20 mM HCOOH in 0.1 M NaClO 4 (pH ∼3.9) at room temperature. This intermediate pH regime was chosen, since the reduction of formic acid is expected to only occur in acidic media [ 8 ] and the HER activity can be reduced under the mild acidic conditions.…”

Dynamics of Heterogeneous Catalytic Processes at Operando Conditions

“…A surface Pourbaix diagram can be obtained through AITD to study the stable surface phases under different potential/pH conditions. 115 Moreover, combining GO methods with AITD is a powerful strategy to construct structural models. After obtaining a series of GM of Cu(111)-supported Zn y O x catalysts through GO, Reichenbach et al 116 performed AITD to further assess, and ensure, the thermodynamic stabilities of these structures under different temperatures and O 2 pressures.…”