H2O2 is a valuable, environmentally friendly oxidizing agent, with a wide range of uses, from the provision of clean water to the synthesis of valuable chemicals. The on-site electrolytic production of H2O2 would bring the chemical to applications beyond its present reach. The successful commercialization of electrochemical H2O2 production requires cathode catalysts with high activity, selectivity and stability. In this Perspective, we highlight our current understanding of the factors that control the cathode performance. We review the influence of catalyst material, electrolyte and the structure of the interface at the mesoscopic scale. We provide original theoretical data on the role of the geometry of the active site and its influence on activity and selectivity. We have also conducted a series of original experiments on (i) the effect of pH on H2O2 production on glassy carbon, pure metals, and metal-mercury alloys, and (ii) the influence of cell geometry and mass transport in liquid half-cells in comparison to membrane electrode assemblies.

Nitrogen-doped carbon materials featuring atomically dispersed metal cations (M−N−C) are an emerging family of materials with potential applications for electrocatalysis. The electrocatalytic activity of M−N−C materials toward four-electron oxygen reduction reaction (ORR) to H 2 O is a mainstream line of research for replacing platinumgroup-metal-based catalysts at the cathode of fuel cells. However, fundamental and practical aspects of their electrocatalytic activity toward two-electron ORR to H 2 O 2 , a future green "dream" process for chemical industry, remain poorly understood. Here we combined computational and experimental efforts to uncover the trends in electrochemical H 2 O 2 production over a series of M−N−C materials (M = Mn, Fe, Co, Ni, and Cu) exclusively comprising atomically dispersed M−N x sites from molecular first-principles to bench-scale electrolyzers operating at industrial current density. We investigated the effect of the nature of a 3d metal within a series of M−N−C catalysts on the electrocatalytic activity/selectivity for ORR (H 2 O 2 and H 2 O products) and H 2 O 2 reduction reaction (H 2 O 2 RR). Co−N−C catalyst was uncovered with outstanding H 2 O 2 productivity considering its high ORR activity, highest H 2 O 2 selectivity, and lowest H 2 O 2 RR activity. The activity−selectivity trend over M−N−C materials was further analyzed by density functional theory, providing molecular-scale understandings of experimental volcano trends for four-and two-electron ORR. The predicted binding energy of HO* intermediate over Co−N−C catalyst is located near the top of the volcano accounting for favorable two-electron ORR. The industrial H 2 O 2 productivity over Co−N−C catalyst was demonstrated in a microflow cell, exhibiting an unprecedented production rate of more than 4 mol peroxide g catalyst −1 h −1 at a current density of 50 mA cm −2 .

Electrochemical CO reduction holds the promise to be a cornerstone for sustainable production of fuels and chemicals. However, the underlying understanding of the carbon–carbon coupling toward multiple-carbon products is not complete. Here we present thermodynamically realistic structures of the electrochemical interfaces, determined by explicit ab initio simulations. We investigate how key CO reduction reaction intermediates are stabilized in different electrolytes and at different pH values. We find that the catalytic trends previously observed experimentally can be explained by the interplay between the metal surface and the electrolyte. For the Cu(100) facet with a phosphate buffer electrolyte, the energy efficiency is found to be limited by blocking of a phosphate anion, while in alkali hydroxide solutions (MOH, M = Na, K, Cs), OH* intermediates may be present, and at high overpotential the H* coverage limits the reaction. The results provide insight into the electrochemical interface structure, revealing the limitations for multiple-carbon products, and offer a direct comparison to experiments.

The electrochemical oxidation of methane to methanol at remote oil fields where methane is flared is the ultimate solution to harness this valuable energy resource. In this study we identify a fundamental surface catalytic limitation of this process in terms of a compromise between selectivity and activity, as oxygen evolution is a competing reaction. By investigating two classes of materials, rutile oxides and two-dimensional transition metal nitrides and carbides (MXenes), we find a linear relationship between the energy needed to activate methane, i.e. to break the first C-H bond, and oxygen binding energies on the surface. Based on a simple kinetic model we can conclude that in order to obtain sufficient activity oxygen has to bind weakly to the surface but there is an upper limit to retain selectivity. Few potentially interesting candidates are found but this relatively simple description enables future large scale screening studies for more optimal candidates.

Electrochemical reactions depend on the electrochemical interface between the electrode surfaces and the electrolytes. To control and advance electrochemical reactions there is a need to develop realistic simulation models of the electrochemical interface to understand the interface from an atomistic point‐of‐view. Here we present a method for obtaining thermodynamic realistic interface structures, a procedure we use to derive specific coverages and to obtain ab initio simulated cyclic voltammograms. As a case study, the method and procedure is applied in a matrix study of three Cu facets in three different electrolytes. The results have been validated by direct comparison to experimental cyclic voltammograms. The alkaline (NaOH) cyclic voltammograms are described by H* and OH*, while in neutral medium (KHCO3) the CO3* species are dominating and in acidic (KCl) the Cl* species prevail. An almost one‐to‐one mapping is observed from simulation to experiments giving an atomistic understanding of the interface structure of the Cu facets. Atomistic understanding of the interface at relevant eletrolyte conditions will further allow realistic modelling of electrochemical reactions of importance for future eletrocatalytic studies.

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Surface redox processes involving oxygen atom exchange are fundamental in catalytic reactions mediated by metal oxides. These processes are often difficult to uncover due to changes in the surface stoichiometry and atomic arrangement. Here we employ high-resolution transmission electron microscopy to study vanadium oxide supported on titanium dioxide, which is of relevance as a catalyst in, e.g., nitrogen oxide emission abatement for environmental protection. The observations reveal a reversible transformation of the vanadium oxide surface between an ordered and disordered state, concomitant with a reversible change in the vanadium oxidation state, when alternating between oxidizing and reducing conditions. The transformation depends on the anatase titanium dioxide surface termination and the vanadium oxide layer thickness, suggesting that the properties of vanadium oxide are sensitive to the supporting oxide. These atomic-resolution observations offer a basis for rationalizing previous reports on shape-sensitive catalytic properties.

We investigate the structural properties and coordination of VO X species supported on the facets of anatase TiO2 as the oxidation state changes during the catalytic cycle of selective catalytic reduction (SCR) of NO X . Density functional theory (DFT) calculations reveal how the molecular structures of hydrated, low-coverage V sites depend on the surface facet of the TiO2 (anatase) support. Thus, the support effect is not limited to only disperse the active phase but also dictates its shape and ultimately its reactivity. We find that hydrated VO X species, where V is present in oxidation state +5, are present in distorted tetrahedral configurations on the most stable TiO2(101) facet, whereas on the less stable TiO2(001) facet they are present in distorted octahedral configurations. Furthermore, we find the reduced states of the same species where V is present in oxidation state +4 also exhibit unchanged local coordination with the vanadyl unit VO intact. We support the findings by electron paramagnetic resonance spectroscopy (EPR) data on a vanadia–titania catalyst partly reduced in situ by ammonia exposure. These results clarify the inconsistencies in the literature and interrelate the spectroscopic observations by Raman and IR with EPR and NMR.