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Mixed-metal oxides are generally considered to be the highest-performance catalysts for alkaline water oxidation. Despite significant efforts dedicated to understanding and accelerating their efficiency, most works have been limited investigations of Ni, Co, and Fe oxides, thus overlooking beneficial effects of hetero-anion incorporation. To this end, we report on the development of Co0.5Fe0.5O0.5F1.5 oxyfluoride materials featuring a rutile crystal structure and porous morphology via a scalable and green synthetic route. The catalyst surface, enhanced through electron withdrawing effects imparted by the fluoride ions, give rise to highly effective catalytic sites for electrochemical water oxidation. In particular, their performance across metrics of Tafel slope (27 mV/dec), mass activity (846 A/g at 1.53 V vs. RHE), turnover frequency (21/s at 1.53 V vs. RHE), overpotential (220 mV for 10 mA/cm2), and stability (27 days of continuous operation) largely surpasses most known Co-based catalysts. Mechanistic studies suggest that this performance is driven by a bimolecular, oxygen coupling reaction mechanism through proximal active sites on the catalyst surface, thus enabling a new avenue for achieving accelerated oxygenic electrocatalysis.

Electrocatalytic formation of C–N bonds was achieved through the electrolysis of CO2 and NH3 over Cu catalysts. A combined analytical and spectroscopic approach gave insights into the reaction mechanism leading to formamide and acetamide products.

Summary The renewable-energy-driven conversion of CO2 is an important means of generating carbon-based fuels and chemicals to power a sustainable society. While most CO2 reduction (CO2R) is carried out in alkaline electrolyte, working in such conditions often leads to spontaneous carbonate formation and, consequently, a low energy balance and CO2 utilization rate. Alternatively, operating in acid alleviates these issues, but achieving selective CO2R in the presence of high proton concentrations has proven to be a challenge over the years. Recently, a host of works have emerged that have demonstrated both a proof of concept and initial design principles for CO2R in acid. As such, this perspective will cover the key initial findings that steer catalysis towards CO2R. After an overview of successful systems, we turn to the future in examining what key questions remain and steps can be taken in this emerging area to bring CO2R in acid toward practical feasibility.

The modularity of molecular catalysts enables the tuning of both active site and peripheral units to maximize functionality, thus rendering them as ideal model systems to explore fundamental concepts in catalysis. Hydrophobicity is often regarded as an undesirable aspect that hinders their dissolution in aqueous electrolytes. In contrast, we modified established Co terpyridine catalysts with hydrophobic perfluorinated alkyl side chains and took advantage of their hydrophobic character by utilizing them not as dissolved species in an aqueous electrolyte but at the gas-liquid-solid interfaces on a gas diffusion electrode (GDE) applied towards the electrochemical reduction of CO2. We found that the self-assembly of these perfluorinated units on the GDE surface results in a catalytic system selective for CH4 production, whereas every other Co terpyridine catalyst reported before was only selective for CO or formate. An array of mechanistic and operando spectroscopic investigations suggests a mechanism in which the pyridine units function as proton shuttles that deliver protons to the dynamic hydrophobic pocket in which CO2 reduction takes place. Finally, optimizing the system by integrating fluorinated carbon nanotubes as a hydrophobic conductive scaffold leads to a Faradaic efficiency for CH4 production above 80% at rates above 10 mA/cm2, thus far unprecedented for a molecular electrocatalytic system.

Co-electrolysis of CO2 with simple N-species is an appealing route to sustainable fabrication of C-N bond containing products. A prominent challenge in, the area is to promote the C-N coupling step in place of the established CO2 reduction pathways. This can be particularly difficult when relying on solution-based species (e.g., NH3) to intercept intermediates that are continually being reduced on heterogeneous catalyst surfaces. In light of this, we introduce pulsed electrocatalysis as a tool for C-N bond formation. The reaction routes opened through this method involve both partial reduction and partial oxidation of separate reactants on the same catalyst surface in parallel to co-adsorb their activated intermediates proximal to one another. Using the CO2 and NH3 as model reactants, the end result is an enhancement of selectivity and formation rates for C-N bond containing products (urea, formamide, acetamide, methylamine) by factors of 3-20 as compared to static electrolysis in otherwise identical conditions. An array of operando measurements and computational modelling was carried out to pinpoint the key factors behind this performance enhancement. Finally, the oxy-reductive coupling strategy was extended to additional carbon and nitrogen reactants as well as applied to boost electrochemical C-S coupling.

The electrochemical conversion of nitrate (NO3-) to ammonia (NH3) is an emerging alternative to valorize this aqueous pollutant to an essential chemical feedstock and potential fuel. Underpinning the maturation of the field and eventual viability of this technology is the discovery of efficient electrocatalysts, coupled with fundamental insights into the reaction mechanism. Until now, fluorinated materials have not yet been explored in this direction. In this work, we present the first fluorinated catalyst used for electrochemical NO3- reduction to NH3. A new copper-based oxyfluoride, Cu3Al2OF10, prepared through a facile coprecipitation and annealing of the corresponding hydrated fluoride r-Cu3Al2F12(H2O)12, was found to be exceptionally active, attaining a NH3 Faradaic Efficiency (FE) of up to 57% for the 8-electron NO3- to NH3 pathway (-0.4 VRHE) with a mass activity of up to 1220 A.g-1 at -0.6 VRHE, the highest yet recorded. Additionally, Cu3Al2OF10 continually produced NH3 for 2.5 days while maintaining a reasonable FE (55%). Finally, electroanalytical and operando spectroscopic investigations revealed a reversible transition to a phase entailing Cu nanoparticles embedded within the amorphous oxyfluoride matrix that was predominantly responsible for the catalyst’s activity. Overall, this work stands to open avenues for transition metal fluoride materials within the field nitrogen-based electrocatalysis.

The formation of C-S bonds is an important step in the synthesis of pharmaceutical, biological, and chemical products. A very attractive green route to C-S bond containing species would be one driven through electrocatalysis using abundant small molecule precursors but examples within this context are largely absent from the literature. To this end, this work demonstrates the use of CO2 and SO32- as cheap building blocks that couple on the surface Cu-based heterogeneous catalysts to form hydroxymethanesulfonate, sulfoacetate and methane sulfonate for the first time, with Faradaic efficiencies of up to 9.5%. A combination of operando measurements and computational modelling reveal that *CHOH formed on metallic Cu is a key electrophilic intermediate that is nucleophilically attacked by SO32- in the principal C-S bond forming step. In all, the proof-of-concept for electrocatalytic C-S bond formation and mechanistic insights gained stand to substantially broaden the scope of the emerging field of electrosynthesis.

The development of earth-abundant catalysts for the oxygen evolution reaction (OER) in acidic media represents a significant challenge in the context of polymer electrolyte membrane (PEM)-based ele...

Metal and covalent organic frameworks (MOFs and COFs) are increasingly finding exceptional utility in electrocatalytic systems. Their chemically defined porous nature grants them key functions that may enhance their electrocatalytic performance relative to conventional molecular or heterogeneous materials. In order to obtain insights into their function, mechanism, and dynamics under electrocatalytic conditions, operando spectroscopy, that which is performed as the catalyst is functioning, has been increasingly applied. This mini review highlights several key works emerging in recent years that have used various operando spectroscopic techniques, namely UV-vis absorption, Raman, Infrared, and X-ray absorption spectroscopy, to investigate electrocatalytic MOFs and COFs. A brief introduction to each technique and how it was applied to investigate MOF/COF-based electrolytic systems is detailed. The unique set of data obtained, interpretations made, and progress attained all point to the power of operando spectroscopy in truly opening the functionality of MOFs and COFs across many aspects of catalysis.

The electrochemical synthesis of hydrogen peroxide (H2O2), a widely used oxidant, is emerging as a green alternative to the conventional anthraquinone method. In this work, Ni-based metal-organic nanosheet (Ni-MONs) catalysts constructed using a variety of linkers were studied as oxygen reduction catalysts. Using a host of analytical techniques, we reveal how modulating the terephthalic acid linker with hydroxy, amine, and fluorine groups impacts the resulting physical and electronic structure of the Ni catalytic sites. These changes further impact the selectivity for H2O2, with the Ni-Amine-MON reaching near 100% Faradaic efficiency at minimal overpotential for the 2e- H2O2 pathway in alkaline electrolyte. Finally, we translate the Ni-Amine-MON catalyst to a gas-diffusion reaction geometry and demonstrate a H2O2 partial current density of 200 mA/cm2 while maintaining 85% Faradaic efficiency. In all, this study puts forth a simple route to catalyst modulation for highly effective H2O2 electrosynthesis.

Electrosynthetic techniques are gaining prominence across the fields of chemistry, engineering and energy science. However, most works within the direction of synthetic heterogeneous electrocatalysis focus on water electrolysis and CO2 reduction. In this work, we moved to expand the scope of this technology by developing a synthetic scheme which couples CO2 and NH3 at a gas-liquid-solid triple-phase boundary to produce species with C-N bonds. Specifically, by bringing in CO2 from the gas phase and NH3 from the liquid phase together over solid copper catalysts, we have succeeded in forming formamide and acetamide products for the first time. In a subsequent complementary step, we have combined electrochemical analysis and a newly developed operando spectroelectrochemical method, capable of probing the aforementioned triple phase boundary, to extract an initial level of mechanistic analysis regarding the reaction pathways of these reactions and the current system’s limitations. We believe that the development and understanding of this set of reaction pathways will play an exceptionally significant role in expanding the community’s understanding of on-surface electrosynthetic reactions as well as push this set of inherently sustainable technologies towards widespread applicability.

The electrochemical oxidation of the biomass platform 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), is an important reaction in the emerging area of renewable energy-powered biomass valorization. A key limitation in this field is the ill-defined nature of the catalytic sites of the highest-performing materials that limits the fundamental insights that can be extracted. To this end, a conductive metal-organic framework-based electrocatalytic model system with well-defined M-O4 active sites for electrochemical HMF oxidation was developed. These materials were found to be highly active towards FDCA generation, with product yields of over 95 %. In parallel, infrared spectroscopy was employed to capture a surface-bound aldehyde group as the key intermediate in the catalytic cycle, which forms once M(II/III) oxidation occurs. This work illustrates the advantage of utilizing molecularly defined active sites coupled with operando spectroscopy to provide fundamental insights into a variety of electrosynthetic reactions and thus paves the way for future catalyst design.

The electrochemical conversion of CO2 to fuels and chemicals is a rapidly growing area of both scientific interest and technological importance. To overcome the challenges of low rates and selectivity on heterogeneous catalysts, efforts are being directed to harness enzyme-mimetic secondary coordination sphere effects to attain a further level of control. These include hydrogen bonding, electrostatics, complexation, and sterics to promote CO2 reduction down a desired pathway on the electrocatalyst surface. This focus review is centered on key advances made in recent years in utilizing secondary coordination sphere effects on heterogeneous catalysts. We discuss how the incorporation of rationally designed electrolyte additives, grafted surface ligands, and chemically tuneable porous scaffolds facilitates enhanced reactivity for CO2 reduction and what advances still need to be made in order to elevate this technology from the lab scale to economic feasibility.

The utilisation of inductive effects is emerging as a powerful tool to enhance material properties. Within the context of electrocatalysis, such effects may alter an active site's electronic structure and consequently, its catalytic activity. To this end, we introduce catalytically active cobalt species within an electron-withdrawing copper fluorophosphate host via a mechanochemical synthetic method. The resulting mixed-metal material features exceptional performance towards electrochemical water oxidation (η of ∼300 mV for 100 mA cm−2) and biomass valorisation (95% selectivity for 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid conversion), thus opening avenues for the rational design of heterogeneous catalysts.

As electrocatalytic technologies are increasingly found in the forefront of renewable energy and sustainability efforts, innovative methods are key towards extracting mechanistic information en route to understanding and consequently maximizing catalyst performance. Here, operando spectroscopy, that which is performed simultaneously as a catalyst is operating, can elucidate reaction pathways, catalyst dynamics and more. However, widely adopted methods such as surface-enhanced Raman spectroscopy (SERS) are not compatible with the full array of relevant catalysts. To this end, shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) is emerging as an enabling technique which allows for highly sensitive Raman spectroscopy to be carried out on non-plasmonic substrates. Judicious design of the plasmonic core, isolating shell and reaction parameters has aided the community in the investigation of important systems such as Pt-catalysed oxygen reduction to understand the interplay of surface-active sites, reaction environment, reaction pathway, and ultimately, performance. The use of SHINERS to extract such structure–activity relationships is the focus of this review. We briefly go over the history of SERS and the advances leading up to SHINERS, provide a critical review of the several state-of-the-art SHINERS studies, and then conclude with a perspective on growing areas in which SHINERS stands to play an important role.

Environmental catalysis has drawn a great deal of attention due to its clean ways to produce useful chemicals or carry out some chemical processes. Photocatalysis and electrocatalysis play important roles in these fields. They can decompose and remove organic pollutants from the aqueous environment, and prepare some fine chemicals. Moreover, they also can carry out some important reactions, such as O2 reduction reaction (ORR), O2 evolution reaction (OER), H2 evolution reaction (HER), CO2 reduction reaction (CO2RR), and N2 fixation (NRR). For catalytic reactions, it is the key to develop high-performance catalysts to meet the demand for targeted reactions. In recent years, two-dimensional (2D) materials have attracted great interest in environmental catalysis due to their unique layered structures, which offer us to make use of their electronic and structural characteristics. Great progress has been made so far, including graphene, black phosphorus, oxides, layered double hydroxides (LDHs), chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks (MOFs), covalent organic frameworks (COFs), and others. This content drives us to invite many famous groups in these fields to write the roadmap on two-dimensional nanomaterials for environmental catalysis. We hope that this roadmap can give the useful guidance to researchers in future researches, and provide the research directions.

With the rising emphasis on renewable energy research, the field of electrocatalytic CO2 conversion to fuels has grown tremendously in recent years. Advances in nanomaterial synthesis and characterization have enabled researchers to screen effects of elemental composition, size, and surface chemistry on catalyst performance. However, direct links from structure and active state to catalytic function are difficult to establish. To this end, operando spectroscopic techniques, those conducted simultaneously as catalysts operate, can provide key complementary information by investigating electrocatalysis under turnover conditions. In particular, Raman and infrared spectroscopy have the potential to reveal the identity of surface-bound intermediates, catalyst active state, and possible reaction sites to supplement the insights extracted from conventional electrochemistry. Such research aims to work in tandem synthetic and catalytic efforts to guide the development of next-generation CO2 electrocatalytic system...

Doping/decorating of graphene or reduced graphene oxide (rGO) with heteroatoms provides a promising route for the development of electrocatalysts which will be useful in many technologies, including water splitting. However, current doping approaches are complicated, not eco-friendly, and not cost-effective. Herein, we report the synthesis of doped/decorated rGO for oxygen evolution reaction (OER) using a simple approach that is cost-effective, sustainable, and easy to scale up. The OER catalyst was derived from the reduction of GO by an exo-electron-transferring bacterium, Geobacter sulfurreducens. Various analytical tools indicate that OER active elements such as Fe, Cu, N, P, and S decorate the rGO flakes. The hybrid catalyst (i.e., Geobacter/rGO) produces a geometric current density of 10 mA cm–2 at an overpotential of 270 mV versus the reversible hydrogen electrode with a Tafel slope of 43 mV dec–1 and possesses high durability, as evidenced through 10 h of stability testing. Electrochemical analyses suggest the importance of Fe and its possible role as an active site for OER. Overall, this work represents a simple approach toward the development of an earth-abundant, eco-friendly, and highly active OER electrocatalyst for various applications such as solar fuel production, rechargeable metal–air batteries, and microbial electrosynthesis.

Electrochemical conversion of abundant feedstocks to fuels and value-added chemicals is rapidly gaining significance as a promising method to harness renewable electricity. To this end, research group develops heterogeneous catalysts (e.g. nanomaterials, MOFs) geared for the reduction of CO2 and oxidation of biomass platforms to fuels and value-added chemicals. Further, we establish strategies in emergent areas of electrocatalysis such as electrochemically forming and cleaving C-N bonds. Because the design of new catalytic systems is inherently linked to a precise understanding of how these reactions proceed on heterogeneous surfaces, we put considerable efforts in developing methodology for operando probing of these systems with vibrational spectroscopy. In all, I show how using these experiments provides key mechanistic information on surface reaction mechanisms that enhance our understanding of functional interfaces and how the research provides avenues for future materials design within the context of renewable energy electrocatalysis.

The electrochemical oxidation of the biomass platform 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), is an important reaction in the emerging area of renewable energy-powered biomass valorization. A key limitation in this field is the ill-defined nature of the catalytic sites of the highest-performing materials that limits the fundamental insights that can be extracted. To this end, a conductive metal-organic framework-based electrocatalytic model system with well-defined M-O

The renewable energy-driven valorization of excess feedstocks into commodity chemicals and societally useful products constitutes a longstanding push in energy and sustainability research. To this end, this work pushes to expand the scope of green electrosynthesis by innovating a new approach to convert acetonitrile, industrially generated in excess and burned off, to in-demand ammonia and acetaldehyde products. Success here was enabled through the use of a Pd-membrane based reactor which abstracted hydrogen atoms from water, which subsequently diffused through to a separate organic compartment in which they carried out the hydrogenation reaction. In this geometry, the reaction proceeded at 5.2 mA/cm2 partial current density and 60% Faradaic efficiency towards ammonia generation. Further, the transmembrane hydrogenation approach gave rise to an onset potential of 0.2VAg/AgCl, surpassing previous state-of-the-art systems by 0.7V. A customized infrared spectroelectrochemcal setup was built up to probe the mechanism of the reaction, which was shown to proceed through an imine hydrolysis like pathway, with the hydrogenation of the NHx species that remained being the rate-limiting steps in the process. This work establishes a new route in electrochemical nitrile hydrogenation and general opens up promising avenues in green electrosynthesis.

The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control. An emerging strategy to generate coordinatively-unsaturated active sites is through the use of organic linkers that lack a functional group that would usually bind with the metal nodes. To execute this strategy, we synthesize a model MOF, Ni-MOF-74 and incorporate a fraction of 2-hydroxyterephthalic acid in place of 2,5-dihydroxyterephthalic acid. The defective MOF, Ni-MOF-74D, is evaluated vs. the nominally defect-free Ni-MOF-74 with a host of ex situ and in situ spectroscopic and electroanalytical techniques, using the oxidation of hydroxymethylfurtural (HMF) as a model reaction. The data indicates that Ni-MOF-74D features a set of 4-coordinate Ni–O4 sites that exhibit unique vibrational signatures, redox potentials, binding motifs to HMF, and consequently superior electrocatalytic activity relative to the original Ni-MOF-74 MOF, being able to convert HMF to the desired 2,5-furandicarboxylic acid at 95% yield and 80% faradaic efficiency. Furthermore, having such rationally well-defined catalytic sites coupled with in situ Raman and infrared spectroelectrochemical measurements enabled the deduction of the reaction mechanism in which co-adsorbed *OH functions as a proton acceptor in the alcohol oxidation step and carries implications for catalyst design for heterogeneous electrosynthetic reactions en route to the electrification of the chemical industry., The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control.

Electrosynthetic techniques are gaining prominence across the fields of chemistry, engineering and energy science. However, most works within the direction of synthetic heterogeneous electrocatalysis focus on water electrolysis and CO2 reduction. In this work, we moved to expand the scope of this technology by developing a synthetic scheme which couples CO2 and NH3 at a gas-liquid-solid triple-phase boundary to produce species with C-N bonds. Specifically, by bringing in CO2 from the gas phase and NH3 from the liquid phase together over solid copper catalysts, we have succeeded in forming formamide and acetamide products for the first time. In a subsequent complementary step, we have combined electrochemical analysis and a newly developed operando spectroelectrochemical method, capable of probing the aforementioned triple phase boundary, to extract an initial level of mechanistic analysis regarding the reaction pathways of these reactions and the current system’s limitations. We believe that the development and understanding of this set of reaction pathways will play an exceptionally significant role in expanding the community’s understanding of on-surface electrosynthetic reactions as well as push this set of inherently sustainable technologies towards widespread applicability.

This work entails the integrated use of electrochemistry and operando Raman spectroscopy to probe the reduction of a biomass platform, furfural, to value-added chemicals on Cu electrodes. The results reveal key strutural differences of the Cu that dictate selectivity for furfural alcohol or 2-methylfuran.

The development of electrochemical technologies is becoming increasingly important due to their growing part in renewable energy conversion and storage. Within this context, metal organic frameworks (MOFs) are finding an important role as electrocatalysts. Specifically, their molecularly defined structure across several lengths scales endows them functionality not accessible with conventional heterogeneous catalysts. To this end, this perspective will focus on the unique features within MOFs and their analogs that enable them to carry out electrocatalytic reactions in unique ways to synthesize fuels and value-added chemicals from abundant building blocks like CO2 and N2. We start with a brief overview of the initial advent of MOF electrocatalysts prior to moving to overview the forefront of the field of MOF-based electrosynthesis. The main discussion focuses on three principal directions in MOF-based electrosynthesis: multifunctional active sites, electronic modulation, and catalytic microenvironments. To conclude, we identify several challenges in the next stage of MOF electrocatalyst development and offer several key directions to take as the field matures.

Enzymes use adaptive catalytic pocket to accelerate catalysis. Recently published in Nature Catalysis, Zhong and coworkers have translated this functionality into a MOF with a Cu-Ni active site in which the Cu-Ni distance changes to stabilize intermediates along the CO2 to CH4 pathway and give rise to exceptional catalytic selectivity.

The allure of metal-organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control. An emerging strategy to generate coordinatively-unsaturated active sites is through the use of organic linkers that lack a functional group that would usually bind with the metal node. To execute this strategy, we synthesize a model MOF, Ni-MOF-74 and incorporate a fraction of 2-hydroxyterephthalic acid in place of 2,5-dihydroxyterephthalic acid. The defective MOF, Ni74D, is evaluated vs. the nominally defect-free Ni74 MOF with a host of ex situ and in situ spectroscopic and electroanalytical techniques, using the oxidation of hydroxymethylfurtural (HMF) as a model reaction. The data indicates that Ni74D features a set of 4-coordinate Ni-O4 sites that exhibit unique vibrational signatures, redox potentials, binding motifs to HMF, and consequently superior electrocatalytic activity relative to the original Ni74 MOF, being able to convert HMF to the desired 2,5- furandicarboxylic acid at 95% yield and 80% Faradaic efficiency. The strategy put forth to rationally design coordinatively-unsaturated electrocatalytic sites and the methodology put forth in investigating their behavior stand to bolster the understanding and growth of the field.

International audience; Surface plasmons are collective oscillations of free electrons at the interface between a conducting material and the dielectric environment. These excitations support the formation of strongly enhanced and confined electromagnetic fields. As well, they display fast dynamics lasting tens of femtoseconds and can lead to a strong nonlinear optical response at the nanoscale. Thus, they represent the perfect tool to drive and control fast optical processes, such as ultrafast optical switching, single photon emission, as well as strong coupling interactions to explore and tailor photochemical reactions. In this Virtual Issue, we gather several important papers published in Nano Letters in the past decade reporting studies on the ultrafast dynamics of surface plasmons.

The integration of enzymes with synthetic materials allows efficient electrocatalysis and production of solar fuels. Here, we couple formate dehydrogenase (FDH) from Desulfovibrio vulgaris Hildenborough (DvH) to metal oxides for catalytic CO 2 reduction and report an in-depth study of the resulting enzyme–material interface. Protein film voltammetry (PFV) demonstrates the stable binding of FDH on metal-oxide electrodes and reveals the reversible and selective reduction of CO 2 to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR-IR) spectroscopy confirm a high binding affinity for FDH to the TiO 2 surface. Adsorption of FDH on dye-sensitized TiO 2 allows for visible-light-driven CO 2 reduction to formate in the absence of a soluble redox mediator with a turnover frequency (TOF) of 11±1 s −1 . The strong coupling of the enzyme to the semiconductor gives rise to a new benchmark in the selective photoreduction of aqueous CO 2 to formate. authorsversion published

Electrocatalysis is a promising route to generate fuels and value-added chemicals from abundant feedstocks powered by renewable electricity. The field of electrocatalysis research has made great progress in supplementing electrocatalyst development with operando vibrational spectroscopic techniques, those carried out simultaneously as the reaction is occurring. Such experiments unveil reaction mechanisms, structure-activity relationships and consequently, accelerate the development of next generation electrocatalytic systems. While operando techniques have now been extensively applied to water electrolysis and CO2 reduction, their application to the emerging area of biomass valorization is rather nascent. The electrocatalytic conversion of biomass can provide an alternate, environmentally friendly route to the chemicals which power our society, but this field still requires much growth before the envisioned technologies are economically competetive with thermochemical routes. Within this context, a growing body of work has begun to translate the methodology and concepts from water/CO2 electrolysis to biomass valorization to elucidate links between catalyst structure, adsorbed surface intermediates, and the resultant catalytic performance. The reactions of interest here include the upgrading of biomass platforms such a 5-hydroxymethylfurfural or glycerol to value-added chemicals. In this feature article we highlight these efforts and provide a critical view on the steps necessary to take to further progress the field. We further show how the knowledge derived from these studies can be translated to a plethora of other organic transformations to forge new avenues in renewable energy electrocatalysis.

Electrocatalytic conversion of biomass-derived intermediates is a green route to value-added chemicals. However, this technology is just emerging and the mechanisms of this process are not fully resolved. Here, we present the first operando Raman spectroscopic investigation of 5-hydroxymethylfurfural oxidation on gold nanoparticle surfaces, opening up avenues for understanding such reactivity and for rational systems design.

Electrocatalytic reduction of carbon dioxide (CO2R) to fuels and chemicals is a pressing scientificand engineering challenge that is, in part, hampered by a lack of understanding of the surface reactionmechanism, even for relatively simple systems. While many efforts have been dedicated to promoting CO2Ron catalytic surfaces by tuning composition, morphology, and defects, the role of the reaction environmentaround the active site, and how this can be leveraged to modulate CO2R, is less clear. To this end, wefocused on a model CO2R catalyst, Ag nanoparticles, and carried out a combined electrocatalytic andoperando Raman spectroscopic investigation of CO2R on their surfaces. Bare Ag and chemically modifiedAg nanoparticles were investigated to understand how the surface reaction environment dictatesintermediate binding and catalytic efficiency en route to CO generation. The results revealed that theprimary product on Ag is CO, which is formed through a doubly-bound CObridge configuration. In contrast,electrografted imidazole and polyvinylpyrrolidone (PVP)-coated Ag feature CO in a singly-bound COatopconfiguration on their surfaces, whereas porous zeolitic-imidazolate framework-coated Ag was observedto bind both CObridge and COatop. Further, another function of the Ag surface modifications is to dictate thetype of Ag surface sites which form Ag-C bonds with CO2R intermediates. Through analysis of the ofelectrochemical and spectroscopic data, we deduce which key aspects of CO2R on Ag surface render aCO2R system efficient and show how surface chemistry dictates diverging CO2R surface reactionmechanisms. The insights gained here are important as they provide the community with a greaterunderstanding of heterogeneous CO2R and can be further translated to a number of catalytic systems.

Extracellular electron transfer (EET) in microorganisms is prevalent in nature and has been utilized in functional bioelectrochemical systems. EET of Geobacter sulfurreducens has been extensively studied and has been revealed to be facilitated through c-type cytochromes, which mediate charge between the electrode and G. sulfurreducens in anodic mode. However, the EET pathway of cathodic conversion of fumarate to succinate is still under debate. Here, we apply a variety of analytical methods, including electrochemistry, UV-vis absorption and resonance Raman spectroscopy, quartz crystal microbalance with dissipation, and electron microscopy, to understand the involvement of cytochromes and other possible electron-mediating species in the switching between anodic and cathodic reaction modes. By switching the applied bias for a G. sulfurreducens biofilm coupled to investigating the quantity and function of cytochromes, as well as the emergence of Fe-containing particles on the cell membrane, we provide evidence of a diminished role of cytochromes in cathodic EET. This work sheds light on the mechanisms of G. sulfurreducens biofilm growth and suggests the possible existence of a nonheme, iron-involving EET process in cathodic mode.

Natural photosynthesis stores sunlight in chemical energy carriers, but it has not evolved for the efficient synthesis of fuels, such as H2. Semi-artificial photosynthesis combines the strengths of natural photosynthesis with synthetic chemistry and materials science to develop model systems that overcome nature’s limitations, such as low-yielding metabolic pathways and non-complementary light absorption by photosystems I and II. Here, we report a bias-free semi-artificial tandem platform that wires photosystem II to hydrogenase for overall water splitting. This photoelectrochemical cell integrated the red and blue light-absorber photosystem II with a green light-absorbing diketopyrrolopyrrole dye-sensitized TiO2 photoanode, and so enabled complementary panchromatic solar light absorption. Effective electronic communication at the enzyme–material interface was engineered using an osmium-complex-modified redox polymer on a hierarchically structured TiO2. This system provides a design protocol for bias-free semi-artificial Z schemes in vitro and provides an extended toolbox of biotic and abiotic components to re-engineer photosynthetic pathways.