Oxygen crossover effect on palladium and platinum based electrocatalysts during formic acid oxidation studied by scanning electrochemical microscopy

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O₂ and H₂ and electrochemical conversion of CO₂. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).

Electrocatalytic Conversion of CO2 to Formate at Low Overpotential by Electrolyte Engineering in Model Molecular Catalysis

An electrolyte engineering strategy was developed for CO₂ reduction into formate with a model molecular catalyst, [Rh(bpy)(Cp*)Cl]Cl, by modifying the solvent (organic or aqueous), the proton source (H₂ O or acetic acid), and the electrode/solution interface with imidazolium- and pyrrolidinium-based ionic liquids (ILs). Experimental and theoretical density functional theory investigations suggested that π⁺ -π interactions between the imidazolium-based IL cation and the reduced bipyridine ligand of the catalyst improved the efficiency of the CO₂ reduction reaction (CO₂ RR) by lowering the overpotential, while granting partial suppression of the hydrogen evolution reaction. This allowed tuning the selectivity towards formate, reaching for this catalyst an unprecedented faradaic efficiency (FE_HCOO -) ≥90 % and energy efficiency of 66 % in acetonitrile solution. For the first time, relevant CO₂ conversion to formic acid/formate was reached at low overpotential (0.28 V) using a homogeneous catalyst in acidic aqueous solution (pH=3.8). These results open up a new strategy based on electrolyte engineering for enhancing carbon balance in CO₂ RR.

Local probe investigation of electrocatalytic activity

As the world energy crisis remains a long-term challenge, development and access to renewable energy sources are crucial for a sustainable modern society. Electrochemical energy conversion devices are a promising option for green energy supply, although the challenge associated with electrocatalysis have caused increasing complexity in the materials and systems, demanding further research and insights. In this field, scanning probe microscopy (SPM) represents a specific source of knowledge and understanding. Thus, our aim is to present recent findings on electrocatalysts for electrolysers and fuel cells, acquired mainly through scanning electrochemical microscopy (SECM) and other related scanning probe techniques. This review begins with an introduction to the principles of several SPM techniques and then proceeds to the research done on various energy-related reactions, by emphasizing the progress on non-noble electrocatalytic materials.

Characterization of LiCoO2 nanoparticle suspensions by single collision events

Transient electrochemical experiments associated with the collisions between hydrothermally synthesized LiCoO₂ (LCO) nanoparticles/aggregates of different sizes and a polarized gold ultramicroelectrode (UME) were used as a new additive-free analytical tool applied to characterize Li ion insertion compounds.

Electrocatalytic studies on imidazolium based ionic liquids: defining experimental conditions

The number of publications devoted to studying electrochemical reactions in room temperature ionic liquids (RTILs) is constantly growing, but very few of them have been devoted to defining proper experimental conditions to obtain reproducible electrochemical results. In this work, we demonstrate that the combination of a proper RTIL purification treatment and a filtered Ar gas stream allow us to obtain featureless voltammograms in [C4mim][BF4], [C4mim][NTf2], and [C4m2im][NTf2], which otherwise present signals associated with different types of impurities such as water and some minor electroactive impurities acquired during the RTIL synthesis process. Moreover, we demonstrate that bubbling Ar, or another inert gas, through the electrolyte in order to purge O2 dissolved in RTILs is one of the major sources of water and O2 impurities incorporated in RTILs within the electrochemical cell. To overcome this source of water uptake, we have incorporated a gas stream purification filter before the gas reaches the RTIL in the electrochemical cell. To illustrate the effect of these impurities in relevant electrocatalytic studies, we study the electrocatalytic reduction of CO2 on Pt nanoparticles and the key role of an appropiate filter when the CO2 gas stream is bubbled within imidazolium based RTILs. Our cyclic voltammetric studies point out that CO2 electroreduction on Pt nanoparticles only presents activity in [C4mim][NTf2] and [C4m2im][NTf2], thus suggesting that the C-2 position on the imidazolium ring is not the key position in CO2 electrochemical reduction. In contrast, the same Pt nanoparticles are inactive towards CO2 electroreduction in [C4mim][BF4], which is a more hydrophilic RTIL.