Liquid organic hydrogen carriers (LOHC) are considered as the safest and most promising candidates for hydrogen storage, meeting the requirements of sufficient weight and volume capacity (over 6 wt%), hydrogenation-dehydrogenation reversibility and low cost. The prospects of catalytic hydrogenation of polycyclic hydrocarbons for the production of LOHC are considered. The comparison shows that electrocatalytic hydrogenation of aromatic LOHC is highly advantageous, since this approach eliminates the use of gaseous hydrogen in the production of “loaded” LOHC and therefore is safer than the conventional hydrogenation. The advantage of electrocatalytic hydrogenation compared to catalytic hydrogenation is that high temperatures are not required. The approaches to increase the efficiency of electrocatalytic hydrogenation are discussed.

Lignocellulosic biomass represents a very huge renewable carbon reservoir to generate derivatives of paramount interest for producing biofuels or value-added chemicals. The main problem to achieve high conversion rate, selectivity and yield from electrooxidation or electro-hydrogenation/hydrogenolysis of the raw biopolymers constituting lignocellulosic biomass (lignin, cellulose, and hemicellulose) into monomers and oligomers (aromatics, sugars, polyols, acids, furans, etc.) is their low solubility and accessibility to catalysts. The search for alternative bio-sourced media represents an important research axis. Derivatives of these biopolymers are interesting building blocks. But these molecules are very complex in structure and possess different chemical functions making their selective electroconversion difficult. The development of nanostructured catalytic materials adapted for the selective activation/conversion of a given chemical bond/function at low overpotentials is a very huge challenge for the future, as well as the design of reactors allowing the conversion of highly concentrated solutions, in order to integrate these electrochemical processes in biorefinery.

Modern proton exchange membrane water electrolyzers rely on noble metal electrocatalysts. The application of Ir and Pt in such electrolyzers is considered a prerequisite for their long-term operation. However, the scarcity of these critical raw materials is the major drawback of this technology. In recent years, the academic community scrutinized the suitability of non-noble metals as alternative electrocatalysts. While these metals still demonstrate relatively low activity and stability, significant progress has been achieved in improving their performance. Here, we briefly overview recent achievements in oxygen evolution electrocatalysis using non-noble metals. We identify and discuss five stabilization strategies: (a) thermodynamic stabilization; (b) suppression of dissolution kinetics; (c) electrolyte engineering; (d) protection of active interfaces; and (e) system-level solutions. We provide critical remarks on the advantages and drawbacks of the strategies. Moreover, following our previous opinions in this journal, we highlight the significance of testing non-noble metal electrocatalysts in real devices. Graphical abstract Download : Download high-res image (259KB) Download : Download full-size image

Electrocatalysis at the interface between two immiscible electrolyte solutions (ITIES) is an emerging field of research, which allows the separation of reactants according to their lipophilicity. Electrocatalysts of various natures (noble metals, carbon-based and inorganic nanomaterials, enzymes, and supramolecular ensembles) are assembled at the ITIES, either spontaneously or following the application of an interfacial Galvani potential difference. While primarily used for the electrocatalysis of the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), recent work has focused on the electrocatalysis of the oxygen evolution reaction (OER) and the electrocatalytic oxidation of elemental sulfur (S8) and an organosulfur compound. Protocols to compare electrocatalytic performances at the ITIES call for careful data analysis and a detailed knowledge of the catalyst’s morphological parameters (e.g., active surface area and catalyst loading). However, standardisation of such protocols at the ITIES has yet to be implemented and is required to allow better comparison of the results from individual biphasic systems.

The advancement of electrocatalysis from fundamental research to application is a process that requires researchers from different fields to co-work seamlessly to be effective. In this mini review, we highlight common problems that are faced when the complexity of novel electrode assemblies, consisting of nanostructured materials, is moved from a fundamental view towards an evaluation for application. When the classical kinetic descriptors such as Butler-Volmer kinetics are applied to complex electrode assemblies, a clear distinction and attribution of material properties versus electrode performance becomes challenging. We emphasize recent advancements to discern and analyse electrocatalysis at composite or nanostructured electrodes. We discuss the origins of inhomogeneities in the electrocatalytic activity of three-dimensional electrodes, how these can be detected and which necessary changes from the classical methods, such as Tafel analysis, can be performed to ensure a sound data acquisition and evaluation.

Highlights • Significant, OER-driven changes in Ni-based materials preclude their active state. • This includes phase transformations of NiO, Ni(OH)2, and NiOOH caused by applied potential, pH changes and ageing. • Under OER conditions, Ni and Fe can experience reversible oxidation to the +IV state. • Lattice oxygen participation in the reaction mechanism can increase OER activity. • The uptake of electrolyte Fe impurities can influence the Ni electronic/geometric structure. Nickel-based catalysts for the alkaline oxygen evolution reaction (OER) demonstrate excellent catalytic performance and stability. However, a lack of fundamental understanding of the dynamic electronic and structural changes that occur under OER conditions inhibits the rational design of new materials. Recent advances in operando spectroscopy and computational modeling techniques have helped to elucidate the electrochemically-driven transformations of Ni-based materials. For reversible transformations, this encompasses an increased understanding of the redox transformations of Ni/Fe centers, the adsorption and desorption of reaction intermediates, oxygen vacancy dynamics, phase transformations, and the mechanism of dissolution and redeposition of surface atoms. Likewise, there have been great advances in scientific understanding of irreversible transformations including phase transformations related to ageing, as well as operando surface reconstruction which involves the growth of new OER active phases. Graphical abstract Download : Download high-res image (230KB) Download : Download full-size image

Highlights • Degradation is a key challenge for earth-abundant electrocatalysts. • Materials degradation needs to be distinguished from operational degradation. • Degradation studies have high demands on experimental design. • Degradation studies require additional physical characterization. • Quantification of electrochemical degradation is urgently needed. Electrocatalysts for the oxygen evolution reaction (OER) are an important component for the transition from fossil to sustainable energy. Commercialization of cost-effective earth-abundant electrocatalysts is in large parts hindered by their degradation. In this short review, I identify common processes leading to a decrease in electrocatalyst activity, followed by an introduction of staple methods to determine degradation electrochemically and by additional physical characterization, which has the potential to remove ambiguities of purely electrochemical studies. I conclude by a summary of the key challenges for an accurate determination of degradation processes and highlight interesting directions to advance the understanding of degradation processes on electrocatalysts in materials-centered model studies. Graphical abstract Download : Download high-res image (193KB) Download : Download full-size image

Metal–air batteries hold the promise of high specific energy and benign, recyclable components, which are critical to the long term goal of eliminating the use of fossil fuels. The critical components of metal–air batteries include the cathode electrocatalysts and the compatible electrolyte, which together enable the oxygen evolution (OER) and oxygen reduction (ORR) reactions, determining much of the battery`s performance. In this review, we summarize the current status of research on bifunctional oxygen electrocatalysts for aqueous electrolytes and look forward to the advances which need to be made to achieve the promise of metal–air batteries.

Boron-doped diamond and titanium suboxides have been proposed as electrode materials for use as anodes in future electrochemical devices, most likely in remote locations for potable water purification, or for specialized disinfection applications in decentralized systems. A comparison is made between electrochemical purification strategies that do not require added chemicals and systems that do, with emphasis given toward Magnéli electrode-based electrochemical disinfection and iodine-based electrochemical disinfection systems. Both systems with and without added chemicals come with advantages and disadvantages. The outlook of these emerging processes concludes this review. Graphical abstract Download : Download high-res image (213KB) Download : Download full-size image