A reduction reaction is half an overall electrochemical process and hydrogen evolution reaction (HER) is the simplest electrocatalytic reduction reaction. Beyond hydrogen, other reduction reactions are more complex with species involved, products formed, and selectivity typically changes as a function of catalyst and potential. This work seeks to provide a combined view on electrocatalytic CO2/CO reduction, NOx reduction and N2 reduction which are all reduction reactions in competition with HER. The thermodynamics of the reactions are compared together with selectivity predictive schemes for aqueous conditions. Recent experimental results are discussed for the three reduction reactions from a predictive theoretical catalytic mindset, which indicate that dissociation mechanisms have entered electrocatalysis for certain catalytic systems at ambient conditions.

Immobilization of thin organic layers bearing specific functional groups onto materials is one of the main strategies to modulate their properties and develop task-specific surfaces. Besides that, ionic liquids (ILs) and their peculiar physicochemical properties have been a major topic of academic research and are now attracting industrial interest. This short review highlights the growing attention given to the encounter between the ILs and diazonium compounds for building organized interfaces. The review explores the different grafting procedures of diazonium in IL including the electrochemical assisted grafting. Particular emphasis will be devoted to the properties of the generated layers and the added value of the IL as a grafting medium.

Extending the detection capabilities of traditional spectroelectrochemical investigations, closed-bipolar electrochemical imaging (c-BPI) has demonstrated its unique ability to spatially resolve and individually address millions to even billions of individual points of detection without the need for any direct electrical connections. Coupling optical and electrochemical signals, the key challenge becomes resolving the optical response at individual closed-bipolar electrodes within an array to successfully image electrochemical heterogeneity. At the heart of this challenge is the choice between electrochemiluminescence or electrogenerated fluorescence reporting systems and the key tradeoff between spatial resolution and photon efficiency. Working to address this tradeoff, we focus on fluorescence as a useful closed-bipolar imaging tool with great potential for sensing the ultra-transient. We consider the advantages as well as the present challenges of electrofluorogenic reporting strategies in order to offer solutions through an examination of existing direct and indirect approaches towards electrochemical fluorescence imaging applicable to closed-bipolar sensing systems.

MXenes, two-dimensional (2D) transition-metal carbides and nitrides with diverse compositions and structures, have attracted notable attention due to their potential as promising alternatives to the conventional Pt-group catalysts for the hydrogen evolution reaction (HER). Hereby, we analyze the state-of-art approaches in theoretical modelling HER in MXenes with the aim of assessing their intrinsic activity for this crucial electrocatalytic reaction, analyze diverse thermodynamic and electronic properties proposed as descriptors, inspect kinetic aspects, and explore linear scaling relations. Ultimately, we present an overview of the challenges, perspectives, and future research of HER in MXenes.

Influence of global warming and climate change caused by the increase of atmospheric CO2 concentration have become more distinct in recent years. There are worldwide efforts for CO2 mitigation, often categorized into carbon capture, utilization, and storage. However, large hurdles in energetics are creating demands for technological breakthroughs. Herein, we review the research progresses in combining CO2 capture and utilization processes, by electrochemical reduction of CO2 directly in the captured media. In the first part, CO2 electroreduction in amine-based sorbents, potentially targeting the point source capture, are covered with the strategies to enhance the performance in terms of energy efficiency and selectivity. Then, regarding the direct air capture of CO2 by using alkaline sorbents, advances in reduction of bicarbonate and carbonate are discussed together with the electrochemical systems design and developments.

Although the concept of merging electrosynthesis with photochemistry has been introduced many decades ago, the actual use of “electrophotocatalysis” in organic synthesis only recently emerged. This perspective highlights how powerful this technology is and how it can help to overcome challenging oxidative or reductive processes. With this aim, it presents several recent chemical transformations which are inaccessible otherwise and discusses the important challenges and opportunities that lie ahead in this vibrant research field.

Developing hydrogen economy significantly relies on water electrolyzers and fuel cells, where electrocatalysts towards the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) play pivotal roles. For generating unusual catalyst species and preventing detrimental catalyst degradations, manipulating catalyst reconstructions is gaining intensive interest. This work reviews current understandings and modulations of reconstructions of representative OER/ORR electrocatalysts for water electrolyzers and fuel cells, covering platinum group metal- (PGM) based and PGM-free ones. By rigorously discussing the most recent progress, we distinguished catalyst reconstruction from self-optimization or electrochemical activation, and emphasized that (engineered) reconstruction does not necessarily yield improved catalytic performance. More importantly, we highlighted the strategy of rationally designing the physicochemical properties of catalysts and managing the electrochemical conditions to achieve superior control of catalyst reconstructions. Through discussing the advances, challenges, and perspectives, this work contributes to rationally reconstructing oxygen catalysts by managing their reconstructions for high-performance hydrogen energy applications.

Electrochemical techniques are coupled with inductively coupled plasma atomic emission spectrometry (ICP-AES) for in-line electrolyte analyses. In this way, a direct measurement of the elemental dissolution rates in real-time or element-resolved electrochemistry can be carried out, complementary to conventional electrochemical measurements of current and potential. This methodology can be used to obtain the element-specific reaction mechanisms under either spontaneous or polarized conditions up to part-per-billion level resolution with applications in diverse domains of corrosion science and interfacial reactivity. This review aims to summarize recent research activities using ICP coupled with other analytical techniques to answer specific questions on the mechanism of degradation of materials in aqueous or organic environments including the dissolution of metal oxides, catalysis, reaction stoichiometry, electrochemical kinetics, and photoelectrochemical reactivity.

Chemical industries largely produce NH3, which has widespread applications in fertilizer, textile, and explosive manufacturing. This study discusses the recent developments in electrochemical NH3 production methods and reviews the advantages and disadvantages of three different electrocatalytic reactions for NH3 production (direct N2 hydrogenation, indirect or mediated N2 reduction followed by chemical NH3 formation, and NOx reduction reaction); additionally, the key challenges in realizing large-scale NH3 production were assessed using sustainable methods. Each method demonstrated specific advantages and limitations for its industrial application and methods that should be improved to replace the Haber-Bosch process on an industrial scale were discussed. Overall, the review indicated that in the future, each NH3 production method should be investigated comprehensively to realize practical and sustainable NH3 production.

Spectroelectrochemistry (SEC) is an integrated technique that marries the best of electrochemistry and spectroscopy during the electron transfer process. The review presents the recent developments in two not-frequently used but promising techniques (Nuclear Magnetic Resonance (NMR) SEC and Dark Field Microscopy (DFM) SEC). The dissemination of these two SEC techniques is required for their future widespread applications. The research challenges and development perspectives of NMR and DFM SEC are elaborated. Furthermore, it is found that employing SEC techniques in microfluidics is becoming a research hotspot. Therefore, Raman and Ultraviolet-Visible-based SEC techniques in microfluidics are discussed. The last section summarizes and elaborates on the inherent challenges with SEC.

Electrochemical sensors that use surface-immobilized DNA to bind analytes and transduce the binding into electrochemical signals, have the potential for rapid, specific, and sensitive detection of bioanalytes via a compact and portable platform. However, accessing the structure of these surfaces/interfaces at the relevant spatial scale (<10 nm), which determines the interfacial interactions and ultimately sensing performance, remains an unsolved challenge. Here, we review studies that have used high resolution atomic force microscope imaging and spatial statistical analysis tools to understand crowding interactions between thiolated DNA probes immobilized on gold electrodes and how such interactions impact target binding. We also review related studies that attempt to control the nanoscale spatial arrangement of the immobilized recognition elements to optimize sensing performance. These efforts have led to new advances in understanding of the structure-function relationships of DNA-based electrochemical biosensors to move the field toward rational engineering of these biosensing interfaces.

Proton-exchange-membrane unitized regenerative fuel cell (PEM-URFC) is a promising energy storage and conversion device for large-scale and long-term applications. Previous research has primarily focused on materials development studies, with performance and durability not evaluated at relevant conditions. Such an approach becomes insufficient for making URFC technology commercially competitive. In this review, we highlight recent progress on high-performing PEM-URFCs, focusing on electrode engineering, key components, and operating approaches that take realistic operating conditions into consideration. Key components of a membrane electrode assembly (MEA), including catalyst layer, diffusion media, and membrane, which require different optimization strategies, are discussed in this review.

Single-atom catalysts (SACs) are heterogenous catalysts with elements in common with coordination compounds. We discuss some fundamental elements required for the successful computational modeling of SACs for electrocatalytic applications. The first two aspects are the role played by the exchange-correlation functional adopted within a given DFT approach and the role of the local coordination of the active transition metal atom. Next, we discuss new intermediates that can form on SACs and that are not present on extended metal electrodes and how to model solvation, with particular emphasis on the fact that on SACs water can not only act as a solvent but also as a ligand. Finally, we discuss challenges related to the inclusion of pH and voltage in the models and some open issue concerning the rational design of new SACs.

The electrochemical measurement of sodium ion concentration has a long history and would appear to be ideally placed to serve as the core methodology for sensors that could detect the early onset of hyponatremia. However, there are still many challenges to be overcome – especially when considering elderly end users. This communication highlights the procedural and technological barriers and highlights advances that have been made in attempting to overcome them.

Single-atom electrocatalysts (SAECs) have attracted extensive attention due to their high atomic utilization, unique activity and selectivity. Compared with traditional electrochemical methods (bulk catalysis) that provide the apparent activity, nanoscale electrochemical approaches (local catalysis) can measure the intrinsic activity and explore the reaction mechanism of SAECs, which moderates the conflict between experimental measurements (i.e., apparent activity) and theoretical calculations (i.e., intrinsic activity). Here, we review recent studies of nanoscale electrochemical approaches to probing SAECs and highlight important advances in the last 2–3 years. We introduce four representative nanoscale electrochemical techniques such as single-entity electrochemistry, electrochemical scanning tunneling microscopy (EC-STM), scanning electrochemical cell microscopy (SECCM), and surface interrogation scanning electrochemical microscopy (SI-SECM), and their applications of SAECs. Meanwhile, we give insightful comments on their technical limitations. Finally, we outlook the potential hyphenated techniques which are attractive for nanoscale electrochemical studies of SAECs.

The conventional electrochemical kinetic theories describe multiphase mass transport and interfacial charge transfer individually by different equations, which are weakly coupled with each other at boundaries. This minireview aims at generalizing the kinetic description of various processes involved in electrochemical energy systems by treating them microscopically in terms of random ion hopping with a dynamic lattice-gas model. The unified kinetic equation thus obtained can be reduced to the continuum equation for ion transport in the bulk and the Butler-Volmer equation at the solid-electrolyte interfaces. Particularly, the standard reaction rate constant in the unified kinetic equation is extracted as a generalized kinetic descriptor of these processes. The application of the generalized theory is also discussed.

The modelling of electrochemical interfaces between a liquid electrolyte and an electrode from a quantum chemical perspective is typically done by performing ab initio molecular dynamics simulations. Thus, the statistical nature of the electrolyte structure can be taken into account by performing the proper averages. However, in order to obtain reliable results for such electrochemical interfaces, the simulations should be performed for sufficiently large systems and sufficiently long times under potential control. These requirements lead to significant challenges for running such simulations which will be addressed in this contribution, together with possible approaches to address these challenges.

The ability of biosensing systems to act selectively and sensitively in complex biological fluids will play a significant role in future healthcare developments. In this short review, we discuss recent advancements in surface modification strategies, which have seen electrochemical biosensors perform with high accuracy in real patient samples (plasma, urine, whole blood, sweat). We discuss novel substrate and interfacial modifications for imparting surfaces with antifouling properties. This has allowed analytical devices to detect cancer biomarkers with a sensitivity of 2 pg/mL in whole blood. We also examine nanobodies (Nbs) for use as robust receptor components, which have recently been shown to have single molecule detection limits of the SARS- CoV-2 S1 spike protein in unprocessed saliva. Although such progress has been made, the review also highlights that current platforms are still limited in their capacity to control biointeractions at the sensing interface and long-term stability continues to be a barrier to many biosensors achieving commercialisation. Finally, future prospects are discussed including the use of stimuli-responsive surfaces for increased control over specific and non-specific biointeractions and on-demand biosensing.

The present contribution aims at presenting some relevant developments in the characterisation of corrosion phenomena in the presence of two commonly employed coating types: organic coatings and inorganic (Portland cement) based coatings; the former acts as physical barriers to water access and aggressive ions to the metallics substrate. But only the cement-based coatings provide an additional chemical protection barrier due to the high pH, favouring steel passivation. Current strategies to improve the performance of these coatings consist of giving them self-healing characteristics, which extend their service life. Electrochemical techniques are significant in characterising healing and self-healing in both scenarios.

This short review describes our efforts to apply scanning tunneling microscopy and atomic force microscopy to provide an understanding of the mechanism of phospholipid bilayer formation at a gold electrode surface. We also show that these scanning probe microscopies provide unique information concerning the insertion and aggregation of antibiotic peptides and the mechanism of amyloid peptide aggregation at model biological membranes. We demonstrate that the electrochemical techniques such as electrochemical impedance spectroscopy and infrared reflection spectroscopy could be conveniently used in these systems to acquire complementary molecular level information concerning the membrane structure and properties of biomolecules embedded or adsorbed at the membrane surface. This information has strong relevance for the development of biosensors.