Electronic interpretations of noble and non-noble metal based electrocatalysts

Abstract

As energy demand and climate change grow, there is an essential need for sustainable energy solutions. Electrocatalysis has demonstrated an irreplaceable role in sustainable development by enabling efficient energy conversion and storage. In particular, the electrocatalytic recycling of CO₂ using renewable energy sources has provided an ideal approach for reducing the carbon footprint. Based on this, hydrocarbons and other energy-rich fuels can be produced via CO₂ reduction reaction (CO₂RR), which converts CO₂ into different value-added chemicals. Researchers have focused on designing and developing electrocatalytic materials and reaction systems for the efficient CO₂RR. Atomic catalysts (ACs) are considered to be a novel, efficient catalyst with excellent efficiency in atom utilisation, as well as unique electronic structures, which enable ACs to display remarkable activity and selectivity toward various catalysis reactions. To stabilize isolated atoms on ACs, specific materials, including porous materials, have been commonly employed as the support of ACs. For example, carbon materials such as Graphdiyne (GDY) have been reported to be a promising support for constructing ACs for electrocatalysis. Moreover, the neighbouring interaction on ACs also demonstrated a special role in the CO₂RR process. Also, the electronic structure of the active metal centre can be modified via neighbouring effects; in particular, neighbouring sites can serve as a second assisted site that participates in the electrocatalysis. A significant challenge in electrochemical CO₂RR is achieving high selectivity toward multi-carbon products, which is attributed to the sluggish carbon-carbon bond formation on the C₂+ pathways. Among all electrocatalytic materials, the copper-based electrocatalysts have been widely used in multi-carbon products in electrochemical CO₂RR. In general, dimerization of two adsorbed *CO intermediates is the critical step on multi-carbon pathways. In particular, alkali metal cations (AM⁺) play a crucial role in the C–C coupling process. Existing research has shown that cation species can facilitate C–C bond formation between intermediates via an electric field and the local pH at the electrode-electrolyte interface. In addition, the intrinsic effects of cations have rarely been discussed. Based on this, we employed density functional theory (DFT) calculations to investigate the direct cation effect on CO dimerization on Cu and Pt surfaces. The DFT calculation revealed that the *OCCO intermediate formation can be promoted by the AM⁺ on Cu and Pt surfaces due to the stabilization effects induced by direct cation coordination. Moreover, we have revealed the strong linear correlation between the reaction energy of *OCCO formation and cation–dimer stabilization. Further electronic investigations also revealed that the stabilization effects from cation-dimer coordination are related to improved charge transfer from the metal sites to the adsorbed intermediate, as well as the modifications of the electronic structure. Recent studies also show that the water structure near the electrocatalyst surface can affect CO₂RR performance. For example, variations in cation size in the electrolytes significantly tune the hydrogen-bonding network. Besides, it is believed that solvation will influence cation stabilization. Based on this, MD and DFT were used to study the solvation properties of AM⁺, and the radial distribution function (RDF) analysis revealed the coordination number (CN) of AM⁺ in aqueous solution. Furthermore, the structure of the solvated cations was determined by DFT calculation with an implicit solvation model, in which the charge distribution analysis showed the trend of reactivity of the cation centre in the solvated ion.