Cyclic two-step electrolysis for stable electrochemical conversion of carbon dioxide to formate

Physicochemical Principles of AC Electrosynthesis: Reversible Reactions

Electrolysis integrates renewable energy into chemical manufacturing and is key to sustainable chemistry. Controlling the waveform beyond direct current (DC) addresses the long-standing obstacle of chemoselectivity, yet it also expands the parameter set to optimize, creating a demand for theoretical predictions. Here, we report the first analytical theory for predicting chemoselectivity in an alternating current (AC) electrosynthesis. The mechanism is a selective reversal of the unwanted redox reaction during periods of opposite polarity, reflected in the final reaction outcome as a time-averaged effect. In the ideal scenario of all redox reactions being reversible, square AC waveform biases the outcome toward more overoxidation/over-reduction, whereas sine AC waveform exhibits the opposite effect. However, in a more realistic scenario of some redox reactions being quasi-reversible, sine AC may behave mostly like square AC. These predictions are in numerical agreement with model experiments employing acetophenone and align qualitatively with the literature precedent. Collectively, this study provides theoretical proof for a growing trend that promotes changing waveforms to overcome limitations challenging to address by varying canonical electrochemical parameters.

Dynamic Control of Asymmetric Charge Distribution for Electrocatalytic Urea Synthesis

Constructing dual catalytic sites with charge density differences is an efficient way to promote urea electrosynthesis from parallelNO 3 - ${\mathrm{NO}}_3^ - $ and CO2 reduction yet still challenging in static system. Herein, a dynamic system is constructed by precisely controlling the asymmetric charge density distribution in an Au-doped coplanar Cu7 clusters-based 3D framework catalyst (Au@cpCu7CF). In Au@cpCu7CF, the redistributed charge between Au and Cu atoms changed periodically with the application of pulse potentials switching between -0.2 and -0.6 V and greatly facilitated the electrosynthesis of urea. Compared with the static condition of pristine cpCu7CF (FEurea = 5.10%), the FEurea of Au@cpCu7CF under pulsed potentials is up to 55.53%. Theoretical calculations demonstrated that the high potential of -0.6 V improved the adsorption of *HNO2 and *NH2 on Au atoms and inhibited the reaction pathways of by-products. While at the low potential of -0.2 V, the charge distribution between Au and Cu atomic sites facilitated the thermodynamic C-N coupling step. This work demonstrated the important role of asymmetric charge distribution under dynamic regulation for urea electrosynthesis, providing a new inspiration for precise control of electrocatalysis.

Programmed alternating current optimization of Cu-catalyzed C-H bond transformations

Direct current (DC) electrosynthesis, which has undergone optimization over the past century, plays a pivotal role in a variety of industrial processes. Alternating current (AC) electrosynthesis, characterized by polarity reversal and periodic fluctuations, may be advantageous for multiple chemical reactions, but apparatus, principles, and application scenarios remain underdeveloped. In this work, we introduce a protocol for programmed AC (pAC) electrosynthesis that systematically adjusts currents, frequencies, and duty ratios. The application of representative pAC waveforms facilitates copper-catalyzed carbon-hydrogen bond cleavage in cross-coupling and difunctionalization reactions that exhibit suboptimal performance under DC and chemical oxidation conditions. Moreover, observing catalyst dynamic variation under diverse waveform applications provides mechanistic insight.

Review on strategies for improving the added value and expanding the scope of CO2 electroreduction products

The electrochemical reduction of CO2 into value-added chemicals has been explored as a promising solution to realize carbon neutrality and inhibit global warming. This involves utilizing the electrochemical CO2 reduction reaction (CO2RR) to produce a variety of single-carbon (C1) and multi-carbon (C2+) products. Additionally, the electrolyte solution in the CO2RR system can be enriched with nitrogen sources (such as NO3-, NO2-, N2, or NO) to enable the synthesis of organonitrogen compounds via C-N coupling reactions. However, the electrochemical conversion of CO2 into valuable chemicals still faces challenges in terms of low product yield, poor faradaic efficiency (FE), and unclear understanding of the reaction mechanism. This review summarizes the promising strategies aimed at achieving selective production of diverse carbon-containing products, including CO, formate, hydrocarbons, alcohols, and organonitrogen compounds. These approaches involve the rational design of electrocatalysts and the construction of coupled electrocatalytic reaction systems. Moreover, this review presents the underlying reaction mechanisms, identifies the existing challenges, and highlights the prospects of the electrosynthesis processes. The aim is to offer valuable insights and guidance for future research on the electrocatalytic conversion of CO2 into carbon-containing products of enhanced value-added potential.

Interfacial Micro-Environment of Electrocatalysis and Its Applications for Organic Electro-Oxidation Reaction

Conventional designing principal of electrocatalyst is focused on the electronic structure tuning, on which effectively promotes the electrocatalysis. However, as a typical kind of electrode-electrolyte interface reaction, the electrocatalysis performance is also closely dependent on the electrocatalyst interfacial micro-environment (IME), including pH, reactant concentration, electric field, surface geometry structure, hydrophilicity/hydrophobicity, etc. Recently, organic electro-oxidation reaction (OEOR), which simultaneously reduces the anodic polarization potential and produces value-added chemicals, has emerged as a competitive alternative to oxygen evolution reaction, and the role IME played in OEOR is receiving great interest. Thus, this article provides a timely review on IME and its applications toward OEOR. In this review, the IME for conventional gas-involving reactions, as a contrast, is first presented, and then the recent progresses of IME toward diverse typical OEOR are summarized; especially, some representative works are thoroughly discussed. Additionally, cutting-edge analytical methods and characterization techniques are introduced to comprehensively understand the role IME played in OEOR. In the last section, perspectives and challenges of IME regulation for OEOR are shared.

Comprehensive Comparisons between Directing and Alternating Current Electrolysis in Organic Synthesis

Organic electrosynthesis has consistently aroused significant interest within both academic and industrial spheres. Despite the considerable progress achieved in this field, the majority of electrochemical transformations have been conducted through the utilization of direct-current (DC) electricity. In contrast, the application of alternating current (AC), characterized by its polarity-alternating nature, remains in its infancy within the sphere of organic synthesis, primarily due to the absence of a comprehensive theoretical framework. This minireview offers an overview of recent advancements in AC-driven organic transformations and seeks to elucidate the differences between DC and AC electrolytic methodologies by probing into their underlying physical principles. These differences encompass the ability of AC to preclude the deposition of metal catalysts, the precision in modulating oxidation and reduction intensities, and the mitigation of mass transfer processes.

The Reversible Electrochemical Interconversion of Formate and CO2 by Formate Dehydrogenase from Cupriavidus necator

The bacterial molybdenum (Mo)-containing formate dehydrogenase (FdsDABG) from Cupriavidus necator is a soluble NAD+-dependent enzyme belonging to the DMSO reductase family. The holoenzyme is complex and possesses nine redox-active cofactors including a bis(molybdopterin guanine dinucleotide) (bis-MGD) active site, seven iron-sulfur clusters, and 1 equiv of flavin mononucleotide (FMN). FdsDABG catalyzes the two-electron oxidation of HCOO- (formate) to CO2 and reversibly reduces CO2 to HCOO- under physiological conditions close to its thermodynamic redox potential. Here we develop an electrocatalytically active formate oxidation/CO2 reduction system by immobilizing FdsDABG on a glassy carbon electrode in the presence of coadsorbents such as chitosan and glutaraldehyde. The reversible enzymatic interconversion between HCOO- and CO2 by FdsDABG has been realized with cyclic voltammetry using a range of artificial electron transfer mediators, with methylene blue (MB) and phenazine methosulfate (PMS) being particularly effective as electron acceptors for FdsDABG in formate oxidation. Methyl viologen (MV) acts as both an electron acceptor (MV2+) in formate oxidation and an electron donor (MV+•) for CO2 reduction. The catalytic voltammetry was reproduced by electrochemical simulation across a range of sweep rates and concentrations of formate and mediators to provide new insights into the kinetics of the FdsDABG catalytic mechanism.

Electrocatalytic Reactions for Converting CO2 to Value-Added Products: Recent Progress and Emerging Trends

Carbon dioxide (CO₂) emissions are an important environmental issue that causes greenhouse and climate change effects on the earth. Nowadays, CO₂ has various conversion methods to be a potential carbon resource, such as photocatalytic, electrocatalytic, and photo-electrocatalytic. CO₂ conversion into value-added products has many advantages, including facile control of the reaction rate by adjusting the applied voltage and minimal environmental pollution. The development of efficient electrocatalysts and improving their viability with appropriate reactor designs is essential for the commercialization of this environmentally friendly method. In addition, microbial electrosynthesis which utilizes an electroactive bio-film electrode as a catalyst can be considered as another option to reduce CO₂. This review highlights the methods which can contribute to the increase in efficiency of carbon dioxide reduction (CO₂R) processes through electrode structure with the introduction of various electrolytes such as ionic liquid, sulfate, and bicarbonate electrolytes, with the control of pH and with the control of the operating pressure and temperature of the electrolyzer. It also presents the research status, a fundamental understanding of carbon dioxide reduction reaction (CO₂RR) mechanisms, the development of electrochemical CO₂R technologies, and challenges and opportunities for future research.

Promote electroreduction of CO2 via catalyst valence state manipulation by surface-capping ligand

Electrochemical CO2 reduction provides a potential means for synthesizing value-added chemicals over the near equilibrium potential regime, i.e., formate production on Pd-based catalysts. However, the activity of Pd catalysts has been largely plagued by the potential-depended deactivation pathways (e.g., [Formula: see text]-PdH to [Formula: see text]-PdH phase transition, CO poisoning), limiting the formate production to a narrow potential window of 0 V to -0.25 V vs. reversible hydrogen electrode (RHE). Herein, we discovered that the Pd surface capped with polyvinylpyrrolidone (PVP) ligand exhibits effective resistance to the potential-depended deactivations and can catalyze formate production at a much extended potential window (beyond -0.7 V vs. RHE) with significantly improved activity (~14-times enhancement at -0.4 V vs. RHE) compared to that of the pristine Pd surface. Combined results from physical and electrochemical characterizations, kinetic analysis, and first-principle simulations suggest that the PVP capping ligand can effectively stabilize the high-valence-state Pd species (Pdδ+) resulted from the catalyst synthesis and pretreatments, and these Pdδ+ species are responsible for the inhibited phase transition from [Formula: see text]-PdH to [Formula: see text]-PdH, and the suppression of CO and H2 formation. The present study confers a desired catalyst design principle, introducing positive charges into Pd-based electrocatalyst to enable efficient and stable CO2 to formate conversion.

MoS2 Passivated Multilayer Graphene Membranes for Li-Ion Extraction From Seawater

Abundant Li resources in the ocean are promising alternatives to refining ore, whose supplies are limited by the total amount and geopolitical imbalance of reserves in Earth's crust. Despite advances in Li⁺ extraction using porous membranes, they require screening other cations on a large scale due to the lack in precise control of pore size and inborn defects. Herein, MoS₂ nanoflakes on a multilayer graphene membrane (MFs-on-MGM) that possess ion channels comprising i) van der Waals interlayer gaps for optimal Li⁺ extraction and ii) negatively charged vertical inlets for cation attraction, are reported. Ion transport measurements across the membrane reveal ≈6- and 13-fold higher selectivity for Li⁺ compared to Na⁺ and Mg²⁺ , respectively. Furthermore, continuous, stable Li⁺ extraction from seawater is demonstrated by integrating the membrane into a H₂ and Cl₂ evolution system, enabling more than 10⁴ -fold decrease in the Na⁺ concentration and near-complete elimination of other cations.

Insight into the Electrochemical CO2-to-Ethanol Conversion Catalyzed by Cu2S Nanocrystal-Decorated Cu Nanosheets

Ethanol (C₂H₅OH) is an economically ideal C₂ product in electrochemical CO₂ reduction. However, the CO₂-to-C₂H₅OH conversion yield has been rather low and the underlying catalytic mechanism remains vague or unexplored in most cases. Herein, by decorating small Cu₂S nanocrystals uniform ly on Cu nanosheets, three desirable features are integrated into the electrocatalyst, including a relatively high positive local charge on Cu (Cu^δ+), abundant interfaces between Cu^δ+ and zero-valence Cu⁰, and a non-flat, stepped catalyst surface, leading to the promoted affinity of *CO, decreased *COCO formation barrier, and thermodynamically preferred *CH₂CHO-to-*CH₃CHO conversion. As a result, a high partial current density of ∼20.7 mA cm^-2 and a Faraday efficiency of 46% for C₂H₅OH are delivered at -1.2 V vs reversible hydrogen electrode in an H-cell containing a 0.1 M KHCO₃ solution. This work proposes an efficient strategy for the high-yield CO₂-to-C₂H₅OH conversion, emphasizing the promise for the industrial production of alcohol and related products from CO₂.

Pt-Co Electrocatalysts: Syntheses, Morphologies, and Applications

Pt-Co electrocatalysts have attracted significant attention because of their excellent performance in many electrochemical reactions. This review focuses on Pt-Co electrocatalysts designed and prepared for electrocatalytic applications. First, the various synthetic methods and synthesis mechanisms are systematically summarized; typical examples and core synthesis parameters are discussed for regulating the morphology and structure. Then, starting with the design and structure-activity relationship of catalysts, the research progress of the morphologies and structures of Pt-Co electrocatalysts obtained based on various strategies, the structure-activity relationship between them, and their properties are summarized. In addition, the important electrocatalytic applications and mechanisms of Pt-Co catalysts, including electrocatalytic oxidation/reduction and bifunctional catalytic reactions, are described and summarized, and their high catalytic activities are discussed on the basis of their mechanism and active sites. Moreover, the advanced electrochemical in situ characterization techniques are summarized, and the challenges and direction concerning the development of high-performance Pt-Co catalysts in electrocatalysis are discussed.

Electrochemical conversion of CO2 to value-added chemicals over bimetallic Pd-based nanostructures: Recent progress and emerging trends

Electrochemical conversion of CO₂ to fuels and chemicals as a sustainable solution for waste transformation has garnered tremendous interest to combat the fervent issue of the prevailing high atmospheric CO₂ concentration while contributing to the generation of sustainable energy. Monometallic palladium (Pd) has been shown promising in electrochemical CO₂ reduction, producing formate or CO depending on applied potentials. Recently, bimetallic Pd-based materials strived to fine-tune the binding affinity of key intermediates is a prominent strategy for the desired product formation from CO₂ reduction. Herein, the recent emerging trends on bimetallic Pd-based electrocatalysts are reviewed, including fundamentals of CO₂ electroreduction and material engineering of bimetallic Pd-electrocatalysts categorized by primary products. Modern analytical techniques on these novel electrocatalysts are also thoroughly studied to get insights into reaction mechanisms. Lastly, we deliberate over the challenges and prospects for Pd-based catalysts for electrochemical CO₂ conversion.

Efficient and Selective CO2 Reduction to Formate on Pd-Doped Pb3 (CO3 )2 (OH)2 : Dynamic Catalyst Reconstruction and Accelerated CO2 Protonation

Exploring catalyst reconstruction under the electrochemical condition is critical to understanding the catalyst structure-activity relationship as well as to design effective electrocatalysts. Herein, a PbF₂ nanocluster is synthesized and its self-reconstruction under the CO₂ reduction condition is investigated. F^- leaching, CO₂ -saturated environment, and application of a cathodic potential induce self-reconstruction of PbF₂ to Pb₃ (CO₃ )₂ (OH)₂ , which effectively catalyze the CO₂ reduction to formate. The in situ formed Pb₃ (CO₃ )₂ (OH)₂ discloses >80% formate Faradaic efficiencies (FEs) across a broad range of potentials and achieves a maximum formate FE of ≈90.1% at -1.2 V versus reversible hydrogen electrode (RHE). Kinetic studies show that the CO₂ reduction reaction (CO₂ RR) on the Pb₃ (CO₃ )₂ (OH)₂ is rate-limited at the CO₂ protonation step, in which proton is supplied by bicarbonate (HCO₃ ^- ) in the electrolyte. To improve the CO₂ RR kinetics, the Pb₃ (CO₃ )₂ (OH)₂ is further doped with Pd (4 wt%) to enhance its HCO₃ ^- adsorption, which leads to accelerated protonation of CO₂ . Therefore, the Pd-Pb₃ (CO₃ )₂ (OH)₂ (4 wt%) reveals higher formate FEs of >90% from -0.8 to -1.2 V versus RHE and reaches a maximum formate FE of 96.5% at -1.2 V versus RHE with a current density of ≈13 mA cm^-2 .

Unraveling the Interfacial Polarization Effect between Pd and Polymeric Carbon Nitride toward Efficient CO2 Electroreduction to CO

The efficient electrochemical conversion of carbon dioxide (CO₂) to carbon monoxide (CO) using renewable energy is an effective route to pursue carbon neutrality. Optimizing the binding energy of CO on palladium (Pd) metal-based materials used in this process is to make sure the timely desorption of CO from their active sites is critical. Tuning the electronic structure of the Pd center is an effective strategy to optimize its catalytic performance. Herein, we rationally design Pd nanoparticles (NPs)/polymeric carbon nitride (CN) (Pd/CN) composite, which alters the electronic structure of Pd by introducing the interfacial polarization effect to accelerate CO desorption and improve CO selectivity of Pd catalyst. The optimized Pd/CN exhibits a CO Faradaic efficiency of 92.7% at -0.9 V versus reversible hydrogen electrode in CO₂-saturated 0.1 M KHCO₃ solution. Experimental investigations and theoretical calculations jointly confirm that the enhanced CO selectivity and stability originate from the electron transfer at the Pd/CN interface, and the weakened *CO adsorption on the palladium hydride surface.

Intercalated Gold Nanoparticle in 2D Palladium Nanosheet Avoiding CO Poisoning for Formate Production under a Wide Potential Window

The electrochemical CO₂ reduction into formate acid over Pd-based catalysts under a wide potential window is a challenging task; CO poisoning commonly occurring on the vulnerable surface of Pd must be overcome. Herein, we designed a two-dimensional (2D) AuNP-in-PdNS electrocatalyst, in which the Au nanoparticles are intercalated in Pd nanosheets, for formate production under a wide potential window from -0.1 to -0.7 V versus a reversible hydrogen electrode. Based on the X-ray absorption spectra (XAS) characterizations, CO accumulation detection, and CO stripping voltammetry measurements, we observed that the intercalated Au nanoparticles could effectively avoid the CO formation and boost the formate production on the Pd nanosheet surface by regulating its electronic structure.

Rational-Designed Principles for Electrochemical and Photoelectrochemical Upgrading of CO2 to Value-Added Chemicals

The chemical transformation of carbon dioxide (CO2 ) has been considered as a promising strategy to utilize and further upgrade it to value-added chemicals, aiming at alleviating global warming. In this regard, sustainable driving forces (i.e., electricity and sunlight) have been introduced to convert CO2 into various chemical feedstocks. Electrocatalytic CO2 reduction reaction (CO2 RR) can generate carbonaceous molecules (e.g., formate, CO, hydrocarbons, and alcohols) via multiple-electron transfer. With the assistance of extra light energy, photoelectrocatalysis effectively improve the kinetics of CO2 conversion, which not only decreases the overpotentials for CO2 RR but also enhances the lifespan of photo-induced carriers for the consecutive catalytic process. Recently, rational-designed catalysts and advanced characterization techniques have emerged in these fields, which make CO2 -to-chemicals conversion in a clean and highly-efficient manner. Herein, this review timely and thoroughly discusses the recent advancements in the practical conversion of CO2 through electro- and photoelectrocatalytic technologies in the past 5 years. Furthermore, the recent studies of operando analysis and theoretical calculations are highlighted to gain systematic insights into CO2 RR. Finally, the challenges and perspectives in the fields of CO2 (photo)electrocatalysis are outlined for their further development.

Bias-Adaptable CO2-to-CO Conversion via Tuning the Binding of Competing Intermediates

CO₂ electroreduction powered by renewable electricity represents a promising method to enclose anthropogenic carbon cycle. Current catalysts display high selectivity toward the desired product only over a narrow potential window due primarily to unoptimized intermediate binding. Here, we report a functional ligand modification strategy in which palladium nanoparticles are encapsulated inside metal-organic frameworks with 2,2'-bipyridine organic linkers to tune intermediate binding and thus to sustain a highly selective CO₂-to-CO conversion over widened potential window. The catalyst exhibits CO faradaic efficiency in excess of 80% over a potential window from -0.3 to -1.2 V and reaches the maxima of 98.2% at -0.8 V. Mechanistic studies show that the 2,2'-bipyridine on Pd surface reduces the binding strength of both *H and *CO, a too strong binding of which leads to competing formate production and CO poison, respectively, and thus enhances the selectivity and stability of CO product.

Voltage cycling process for the electroconversion of biomass-derived polyols

Electrification of chemical reactions is crucial to fundamentally transform our society that is still heavily dependent on fossil resources and unsustainable practices. In addition, electrochemistry-based approaches offer a unique way of catalyzing reactions by the fast and continuous alteration of applied potentials, unlike traditional thermal processes. Here, we show how the continuous cyclic application of electrode potential allows Pt nanoparticles to electrooxidize biomass-derived polyols with turnover frequency improved by orders of magnitude compared with the usual rates at fixed potential conditions. Moreover, secondary alcohol oxidation is enhanced, with a ketoses-to-aldoses ratio increased up to sixfold. The idea has been translated into the construction of a symmetric single-compartment system in a two-electrode configuration. Its operation via voltage cycling demonstrates high-rate sorbitol electrolysis with the formation of H2 as a desired coproduct at operating voltages below 1.4 V. The devised method presents a potential approach to using renewable electricity to drive chemical processes.

Alternating Current Electrolysis as Efficient Tool for the Direct Electrochemical Oxidation of Hydroxamic Acids for Acyl Nitroso Diels-Alder Reactions

The acyl nitroso Diels-Alder reaction of 1,3-dienes with electrochemically oxidised hydroxamic acids is described. By using alternating current electrolysis, their typical electro-induced decomposition could be suppressed in favour of the 1,2-oxazine cycloaddition products. The reaction was optimised using Design of Experiments (DoE) and a sensitivity test was conducted. A mixture of triethylamine/hexafluoroisopropanol served as supporting electrolyte in dichloromethane, thus giving products of high purity after evaporation of the volatiles without further purification. The optimised reaction conditions were applied to various 1,3-dienes and hydroxamic acids, giving up to 96 % isolated yield.

Spontaneously Sn-Doped Bi/BiOx Core-Shell Nanowires Toward High-Performance CO2 Electroreduction to Liquid Fuel

Electrochemical CO₂ reduction provides a promising strategy to product value-added fuels and chemical feedstocks. However, it remains a grand challenge to further reduce the overpotentials and increase current density for large-scale applications. Here, spontaneously Sn doped Bi/BiOx nanowires (denoted as Bi/Bi(Sn)O_x NWs) with a core-shell structure were synthesized by an electrochemical dealloying strategy. The Bi/Bi(Sn)O_x NWs exhibit impressive formate selectivity over 92% from -0.5 to -0.9 V versus reversible hydrogen electrode (RHE) and achieve a current density of 301.4 mA cm^-2 at -1.0 V vs RHE. In-situ Raman spectroscopy and theoretical calculations reveal that the introduction of Sn atoms into BiO_x species can promote the stabilization of the *OCHO intermediate on the Bi(Sn)O_x surface and suppress the competitive H₂/CO production. This work provides effective in situ construction of the metal/metal oxide hybrid composites with heteroatom doping and new insights in promoting electrochemical CO₂ conversion into formate for practical applications.

Comparative analysis of biological versus chemical synthesis of palladium nanoparticles for catalysis of chromium (VI) reduction

The discharge of hexavalent chromium [Cr(VI)] from several anthropogenic activities leads to environmental pollution. In this study, we explore a simple yet cost effective method for the synthesis of palladium (Pd) nanoparticles for the treatment of Cr(VI). The presence of elemental Pd [Pd(0)] was confirmed by scanning electron microscope (SEM), electron dispersive spectroscopy and X-ray diffraction (XRD). We show here that the biologically synthesized nanoparticles (Bio-PdNPs) exhibit improved catalytic reduction of Cr(VI) due to their size being smaller and also being highly dispersed as compared to chemically synthesized nanoparticles (Chem-PdNPs). The Langmuir–Hinshelwood mechanism was successfully used to model the kinetics. Using this model, the Bio-PdNPs were shown to perform better than Chem-PdNPs due to the rate constant (k_bio = 6.37 mmol s⁻¹ m⁻²) and Cr(VI) adsorption constant (K_Cr(VI),bio = 3.11 × 10⁻² L mmol⁻¹) of Bio-PdNPs being higher than the rate constant (k_chem = 3.83 mmol s⁻¹ m⁻²) and Cr(VI) adsorption constant (K_Cr(VI),chem = 1.14 × 10⁻² L mmol⁻¹) of Chem-PdNPs. In addition, product inhibition by trivalent chromium [Cr(III)] was high in Chem-PdNPs as indicated by the high adsorption constant of Cr(III) in Chem-PdNPs of K_Cr(III),chem = 52.9 L mmol⁻¹ as compared to the one for Bio-PdNPs of K_Cr(III),bio = 2.76 L mmol⁻¹.

Assembly of a Metal-Organic Framework (MOF) Membrane on a Solid Electrocatalyst: Introducing Molecular-Level Control Over Heterogeneous CO2 Reduction

Electrochemically active Metal‐Organic Frameworks (MOFs) have been progressively recognized for their use in solar fuel production schemes. Typically, they are utilized as platforms for heterogeneous tethering of exceptionally large concentration of molecular electrocatalysts onto electrodes. Yet so far, the potential influence of their extraordinary chemical modularity on electrocatalysis has been overlooked. Herein, we demonstrate that, when assembled on a solid Ag CO₂ reduction electrocatalyst, a non‐catalytic UiO‐66 MOF acts as a porous membrane that systematically tunes the active site's immediate chemical environment, leading to a drastic enhancement of electrocatalytic activity and selectivity. Electrochemical analysis shows that the MOF membrane improves catalytic performance through physical and electrostatic regulation of reactants delivery towards the catalytic sites. The MOF also stabilizes catalytic intermediates via modulation of active site's secondary coordination sphere. This concept can be expanded to a wide range of proton‐coupled electrochemical reactions, providing new means for precise, molecular‐level manipulation of heterogeneous solar fuels systems.

Designing Atomically Dispersed Au on Tensile-Strained Pd for Efficient CO2 Electroreduction to Formate

Pd is one of the most effective catalysts for the electrochemical reduction of CO₂ to formate, a valuable liquid product, at low overpotential. However, the intrinsically high CO affinity of Pd makes the surface vulnerable to CO poisoning, resulting in rapid catalyst deactivation during CO₂ electroreduction. Herein, we utilize the interaction between metals and metal-organic frameworks to synthesize atomically dispersed Au on tensile-strained Pd nanoparticles showing significantly improved formate production activity, selectivity, and stability with high CO tolerance. We found that the tensile strain stabilizes all reaction intermediates on the Pd surface, whereas the atomically dispersed Au selectively destabilizes CO* without affecting other adsorbates. As a result, the conventional COOH* versus CO* scaling relation is broken, and our catalyst exhibits 26- and 31-fold enhancement in partial current density and mass activity toward electrocatalytic formate production with over 99% faradaic efficiency, compared to Pd/C at -0.25 V versus RHE.

Recent Advances in Paired Electrosynthesis

Progress in electroorganic synthesis is linked to innovation of new synthetic reactions with impact on medicinal chemistry and drug discovery and to the desire to minimise waste and to provide energy-efficient chemical transformations for future industrial processes. Paired electrosynthetic processes that combine the use of both anode and cathode (convergent or divergent) with minimal (or without) intentionally added electrolyte or need for additional reagents are of growing interest. In this overview, recent progress in developing paired electrolytic reactions is surveyed. The discussion focuses on electrosynthesis technology with proven synthetic value for the preparation of small molecules. Reactor types are contrasted and the concept of translating light-energy driven photoredox reactions into paired electrolytic reactions is highlighted as a newly emerging trend.

Efficient electroreduction of CO2 to C2+ products on CeO2 modified CuO

Electrocatalytic reduction of CO₂ into multicarbon (C₂₊) products powered by renewable electricity offers one promising method for CO₂ utilization and promotes the storage of renewable energy under an ambient environment. However, there is still a dilemma in the manufacture of valuable C₂₊ products between balancing selectivity and activity. In this work, cerium oxides were combined with CuO (CeO₂/CuO) and showed an outstanding catalytic performance for C₂₊ products. The faradaic efficiency of the C₂₊ products could reach 75.2% with a current density of 1.21 A cm⁻². In situ experiments and density functional theory (DFT) calculations demonstrated that the interface between CeO₂ and Cu and the subsurface Cu₂O coexisted in CeO₂/CuO during CO₂RR and two competing pathways for C–C coupling were promoted separately, of which hydrogenation of *CO to *CHO is energetically favoured. In addition, the introduction of CeO₂ also enhanced water activation, which could accelerate the formation rate of *CHO. Thus, the selectivity and activity for C₂₊ products over CeO₂/CuO can be improved simultaneously.

CO₂ can be efficiently converted into C₂₊ products on CeO₂ modified CuO catalysts and the faradaic efficiency could reach 75.2% with a current density of 1.21 A cm⁻².

Introducing climate change into the biochemistry and molecular biology curriculum

Our climate is changing due to anthropogenic emissions of greenhouse gases from the production and use of fossil fuels. Present atmospheric levels of CO₂ were last seen 3 million years ago, when planetary temperature sustained high Arctic camels. As scientists and educators, we should feel a professional responsibility to discuss major scientific issues like climate change, and its profound consequences for humanity, with students who look up to us for knowledge and leadership, and who will be most affected in the future. We offer simple to complex backgrounds and examples to enable and encourage biochemistry educators to routinely incorporate this most important topic into their classrooms.

Towards the Large-Scale Electrochemical Reduction of Carbon Dioxide

The severe increase in the CO2 concentration is a causative factor of global warming, which accelerates the destruction of ecosystems. The massive utilization of CO2 for value-added chemical production is a key to commercialization to guarantee both economic feasibility and negative carbon emission. Although the electrochemical reduction of CO2 is one of the most promising technologies, there are remaining challenges for large-scale production. Herein, an overview of these limitations is provided in terms of devices, processes, and catalysts. Further, the economic feasibility of the technology is described in terms of individual processes such as reactions and separation. Additionally, for the practical implementation of the electrochemical CO2 conversion technology, stable electrocatalytic performances need to be addressed in terms of current density, Faradaic efficiency, and overpotential. Hence, the present review also covers the known degradation behaviors and mechanisms of electrocatalysts and electrodes during electrolysis. Furthermore, strategic approaches for overcoming the stability issues are introduced based on recent reports from various research areas involved in the electrocatalytic conversion.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Alloyed Palladium-Silver Nanowires Enabling Ultrastable Carbon Dioxide Reduction to Formate

Palladium can enable the electrochemical CO₂ reduction to formate with nearly zero overpotential and good selectivity. However, it usually has very limited stability owing to CO poisoning from the side reaction intermediate. Herein, it is demonstrated that alloying palladium with silver is a viable strategy to significantly enhance the electrocatalytic stability. Palladium-silver alloy nanowires are prepared in aqueous solution with tunable chemical compositions, large aspect ratio, and roughened surfaces. Thanks to the unique synergy between palladium and silver, these nanowires exhibit outstanding electrocatalytic performances for selective formate production. Most remarkably, impressive long-term stability is measured even at < -0.4 V versus reversible hydrogen electrode where people previously believed that formate cannot be stably formed on palladium. Such stability results from the enhanced CO tolerance and selective stabilization of key reaction intermediates on alloy nanowires as supported by detailed electrochemical characterizations and theoretical computations.

Understanding the Voltammetry of Bulk CO Electrooxidation in Neutral Media through Combined SECM Measurements

Recently, the bulk electrooxidation of CO on gold or platinum has been used to detect CO produced during CO₂ reduction in neutral media. The CO bulk oxidation voltammetry may show two distinct peaks depending on the reaction conditions, which up to now have not been understood. We have used scanning electrochemical microscopy (SECM) to probe CO oxidation and pH in the diffusion layer during CO₂ reduction. Our results show that the two different peaks are due to diffusion limitation by two different species, namely, CO and OH^-. We find that between pH 7 and 11, CO oxidation by water and OH^- gives rise to the first and second peak observed in the voltammetry, respectively. Additional rotating disc experiments showed that specifically in this pH range the current of the second peak is diffusion limited by the OH^- concentration, since it is lower than the CO concentration.

Electrode Materials in Modern Organic Electrochemistry

The choice of electrode material is critical for achieving optimal yields and selectivity in synthetic organic electrochemistry. The material imparts significant influence on the kinetics and thermodynamics of electron transfer, and frequently defines the success or failure of a transformation. Electrode processes are complex and so the choice of a material is often empirical and the underlying mechanisms and rationale for success are unknown. In this review, we aim to highlight recent instances of electrode choice where rationale is offered, which should aid future reaction development.

Coupled Electrochemical and Microbial Catalysis for the Production of Polymer Bricks

Power-to-X technologies have the potential to pave the way towards a future resource-secure bioeconomy as they enable the exploitation of renewable resources and CO2 . Herein, the coupled electrocatalytic and microbial catalysis of the C5 -polymer precursors mesaconate and 2S-methylsuccinate from CO2 and electric energy by in situ coupling electrochemical and microbial catalysis at 1 L-scale was developed. In the first phase, 6.1±2.5 mm formate was produced by electrochemical CO2 reduction. In the second phase, formate served as the substrate for microbial catalysis by an engineered strain of Methylobacterium extorquens AM-1 producing 7±2 μm and 10±5 μm of mesaconate and 2S-methylsuccinate, respectively. The proof of concept showed an overall conversion efficiency of 0.2 % being 0.4 % of the theoretical maximum.

Recent Advances in the Catalyst Design and Mass Transport Control for the Electrochemical Reduction of Carbon Dioxide to Formate

Closing the carbon cycle by the electrochemical reduction of CO2 to formic acid and other high-value chemicals is a promising strategy to mitigate rapid climate change. The main barriers to commercializing a CO2 reduction reaction (CO2RR) system for formate production are the chemical inertness, low aqueous solubility, and slow mass transport characteristics of CO2, along with the low selectivity and high overpotential observed in formate production via CO2 reduction. To address those problems, we first explain the possible reaction mechanisms of CO2RRs to formate, and then we present and discuss several strategies to overcome the barriers to commercialization. The electronic structure of the catalyst can be tuned to favor a specific intermediate by adjusting the catalyst composition and tailoring the facets, edges, and corners of the catalyst to better expose the active sites, which has primarily led to increased catalytic activity and selectivity. Controlling the local pH, employing a high-pressure reactor, and using systems with three-phase boundaries can tune the mass transport properties of reactants at the catalyst surface. The reported electrocatalytic performances are summarized afterward to provide insight into which strategies have critical effects on the production of formate.

A Sustainable Chemicals Manufacturing Paradigm Using CO2 and Renewable H2

The chemical industry must decarbonize to align with UN Sustainable Development Goals. A shift toward circular economies makes CO2 an attractive feedstock for producing chemicals, provided renewable H2 is available through technologies such as supercritical water (scH2O) gasification. Furthermore, high carbon and energy efficiency is paramount to favorable techno-economics, which poses a challenge to chemo-catalysis. This study demonstrates continuous gas fermentation of CO2 and H2 by the cell factory, Cupriavidus necator, to (R,R)-2,3-butanediol and isopropanol as case studies. Although a high carbon efficiency of 0.75 [(C-mol product)/(C-mol CO2)] is exemplified, the poor energy efficiency of biological CO2 fixation requires ∼8 [(mol H2)/(mol CO2)], which is techno-economically infeasible for producing commodity chemicals. Heat integration between exothermic gas fermentation and endothermic scH2O gasification overcomes this energy inefficiency. This study unlocks the promise of sustainable manufacturing using renewable feedstocks by combining the carbon efficiency of bio-catalysis with energy efficiency enforced through process engineering.

Catalyst-electrolyte interface chemistry for electrochemical CO2 reduction

The electrochemical reduction of CO2 stores intermittent renewable energy in valuable raw materials, such as chemicals and transportation fuels, while minimizing carbon emissions and promoting carbon-neutral cycles. Recent technoeconomic reports suggested economically feasible target products of CO2 electroreduction and the relative influence of key performance parameters such as faradaic efficiency (FE), current density, and overpotential in the practical industrial-scale applications. Furthermore, fundamental factors, such as available reaction pathways, shared intermediates, competing hydrogen evolution reaction, scaling relations of the intermediate binding energies, and CO2 mass transport limitations, should be considered in relation to the electrochemical CO2 reduction performance. Intensive research efforts have been devoted to designing and developing advanced electrocatalysts and improving mechanistic understanding. More recently, the research focus was extended to the catalyst environment, because the interfacial region can delicately modulate the catalytic activity and provide effective solutions to challenges that were not fully addressed in the material development studies. Herein, we discuss the importance of catalyst-electrolyte interfaces in improving key operational parameters based on kinetic equations. Furthermore, we extensively review previous studies on controlling organic modulators, electrolyte ions, electrode structures, as well as the three-phase boundary at the catalyst-electrolyte interface. The interfacial region modulates the electrocatalytic properties via electronic modification, intermediate stabilization, proton delivery regulation, catalyst structure modification, reactant concentration control, and mass transport regulation. We discuss the current understanding of the catalyst-electrolyte interface and its effect on the CO2 electroreduction activity.