Computational screening for selective catalysts: Cleaving the C C bond during ethanol electro-oxidation reaction

Abstract

The efficiency of direct ethanol fuel cells suffers from the partial oxidation of ethanol into acetic acid as opposed to the complete oxidation of this fuel to CO 2 . Herein, we support the quest for a selective catalyst for ethanol electro-oxidation to CO 2 , building on our previous mechanistic hypothesis based on experimental insight and DFT computations. We derive a simple descriptor of the expected selectivity towards full oxidation, Ω, as a function of the adsorption energy of atomic C and O. Three different families of catalyst surfaces are screened using this descriptor: monometallics, bimetallics and conducting metal oxides, totaling to 600 surfaces. In agreement with available experimental data, no single metal surface is more selective for total oxidation than platinum and palladium. While the selected conducting oxides were not predicted to be selective towards splitting the C-C bond, structurally-controlled monometallics (such as Pd (100)) or some bimetallics (Pd 3 Ag) are found to be competitive with the most stable facet, (111), of Pd and Pt. Despite this very extensive screening, no very promising catalyst has been identified. This highlights the need to identify catalysts for acetate oxidation or to exploit support effects and electrolyte engineering to profit from the full power of direct ethanol fuel cells.

Atomistic modeling of electrocatalysis: Are we there yet?

“…It turns out that in practice simple descriptors, such as the adsorption energy of atoms (typically H, O, N, and C) are a close enough proxy for the determination of volcano curves. The advantage of these very simple descriptors is that they allow to screen a very large number of similar materials (e.g., surface alloys) at modest computational cost 8,9,47–49 …”

“…The advantage of these very simple descriptors is that they allow to screen a very large number of similar materials (e.g., surface alloys) at modest computational cost. 8,9,[47][48][49] The slopes of the volcano tend to be linear. This has led to a second highly important concept: the "universal" scaling relationships, [50][51][52] which describe the fact that the adsorption energy of various intermediates cannot be tuned independently.…”

“…However, this second assumption is not necessary and some authors use the CHE in conjunction with solvation effects. 91,92 A lot of DFT-based research in electrocatalysis studies relies on the CHE approach as a tool to design the catalytic activities of different materials, 47,49,93,94 determine phase diagrams 95 and estimate the free energy of various electroreduction and electrooxidation reactions such as the oxygen reduction reaction, 96 the oxygen evolution reaction, 97 the HER, [98][99][100] the CO 2 reduction reaction, [101][102][103] and the N 2 reduction reaction. 104,105 Despite these exploitable results, CHE has several limitations and unanswered questions remain related to the approximations in establishing the model.…”

Chemical Design of Palladium‐Based Nanoarchitectures for Catalytic Applications

“…In the case of electrooxidation of ethanol, incomplete oxidation of ethanol sometimes occurs due to the decreased capability of Pd to break the CC bond when the ethanol oxidation goes through the C 2 pathway . Therefore, by alloying Pd with other element(s), it becomes possible to completely oxidize ethanol into CO 2 . Meanwhile, in the case of cathodic catalyst, increased alcohol crossover tolerance can be achieved by weakening the bond strength of the oxygenated species on the catalyst surface.…”

Síntese de eletrocatalisadores de PtRh/C-ITO pelo método de borohidreto de sódio para eletrooxidação do etanol em meio alcalino

“…O MEA pode ser constituído com eletrólito de Nafion ® ou outra membrana condutora de prótons como, por exemplo, a de álcool poli vinílico (PVA), mas também existem pesquisas envolvendo membranas a base de amônia e condutoras de ânions[31,32].Muitos estudos buscam entender melhor os mecanismos envolvendo a ROE, seus produtos formados e como se dá a oxidação de intermediários. O entendimento do mecanismo reacional possibilita a escolha de eletrocatalisadores mais seletivos e eficientes[3,13,[36][37][38][39][40][41].…”