Breaking Scaling Relations for Selective Electrochemical Methane Activation to Methanol

ECS Meeting Abstracts, vol. MA2025-01, pp. 2511

Abstract

Methane, the predominant component of natural gas, plays a crucial role in energy production and could serve as a valuable feedstock for direct chemical synthesis due to its abundance. However, its intrinsic chemical stability and low reactivity present significant challenges in fully harnessing its potential. Efficient activation methods are essential to unlock the energy stored in methane and utilize it effectively for chemical synthesis. In this study, we introduce a novel approach to methane activation by exploring surface alloys with unique structures. Specifically, we investigated selective step decoration, a technique where metal ad-atoms are strategically positioned along the step-edges of a metal substrate. This approach creates model alloy surfaces with known compositions and structures that expose two metal atoms at the surface, offering potential pathways to enhance catalytic activity and selectivity for methane activation. Using Density Functional Theory (DFT) modeling, we examined the adsorption properties of key methane activation intermediates (*C, *CH, *CH₂, *CH₃, CH₂O*, CH₃OH, and CH₂O*) on a range of stepped surfaces denoted as M (553), where M represents various transition metals. To evaluate the potential of step-decorated surfaces as better catalysts compared to pure metal catalysts, we calculated and ranked the activity and selectivity of all the catalysts for CH₄ activation, based on their activity and selectivity for producing CH₃OH as the desired product. Our study shows that decorated step surfaces significantly alter the scaling relations which limit catalytic performance on pure metals. For CH₄ intermediates (CH₃, CH₂, CH, - (CHₓ)), there is a linear scaling between the adsorption energy of C and CHₓ on pure metals. However, on decorated step surfaces, these scaling relations are significantly altered (with more scattered data points), or even completely broken. To further investigate the selectivity and activity of the ranked catalysts, we identified five distinctive model surfaces that demonstrated notable performance: (1) Pure Pt (553), (2) Pd (553), (3) Au (553), (4) Pt* on Pd (553), and (5) Pt* on Au (553). These surfaces show higher activity and selectivity (towards *CH3, CH3OH) compared to the other modeled surfaces. Since our goal is electrochemical methane activation, we also investigated the competition between water-derived adsorbed radical (O, OH, and H) and methane intermediate formation at active sites, which can limit catalytic performance. By elucidating the mechanisms underlying performance disparities among these surfaces, including considering lattice strain effects, ligand effects, and ensemble effects—we aim to identify innovative strategies for tuning the electronic and geometric properties of catalyst surfaces. Step decoration in particular can break the well-known scaling relations among carbon-containing adsorbates and could facilitate efficient methane activation, and may be a more general approach to the design of improved electrocatalysts.

Authors 2

1. Onyinyechukwu Goodness Njoku

   Clarkson University

   Affiliation as printed

   Clarkson University

2. Ian T. McCrum Aachen

   Leiden University · Clarkson University

   Affiliation as printed

   Clarkson University

   Leiden University