Electrocatalytic Coupling of Nitrate and Formaldehyde for Hexamethylenetetramine Synthesis via C-N Bond Construction and Ring Formation.

Hexamethylenetetramine (HMTA) is extensively used in the defense industry, medicines, food, plastics, rubber, and other applications. Traditional organic synthesis of HMTA relies on ammonia derived from the Haber process at high temperatures and pressures. In contrast, electrochemical methods enable a safe and green one-pot synthesis of HMTA from waste NO3-. However, HMTA synthesis through the electrochemical method is challenging owing to the complex reaction pathways involving C-N bond construction and ring formation. In this study, HMTA was efficiently synthesized over electrochemical oxidation-derived copper (e-OD-Cu), with a yield of 76.8% and a Faradaic efficiency of 74.9% at -0.30 VRHE. The catalytic mechanism and reaction pathway of HMTA synthesis on e-OD-Cu were investigated through a series of in situ characterization methods and density-functional theory calculations. The results demonstrated that the electrocatalytic synthesis of HMTA involved a tandem electrochemical-chemical reaction. Additionally, the results indicated that the presence of Cu vacancies enhanced substrate adsorption and inhibited the further hydrogenation of C═N. Overall, this study provides an electrocatalytic method for HMTA synthesis and an electrochemical strategy for constructing multiple C-N bonds.

Hydrogen Electrode Reactions in Energy-Related Electrocatalysis Systems.

Hydrogen electrode reactions, including hydrogen evolution reactions and hydrogen oxidation reactions, are fundamental and crucial within aqueous electrochemistry. Particularly in energy-related electrocatalysis processes, there is a consistent involvement of hydrogen-related electrochemical processes, underscoring the need for in-depth study. This review encompasses significant reports, delving into elementary steps and reaction mechanisms of hydrogen electrode reactions, as well as catalyst design strategies. In addition, we focus on the application of hydrogen electrode reaction mechanism in different energy-related electrocatalytic reactions, and the significance of the promotion and suppression of reaction kinetics in different reaction systems. It thoroughly elucidated the significance of these reactions and the need for a deeper understanding, offering a novel perspective for the future development of this field.

Combining anodic alcohol oxidative coupling for C-C bond formation with cathodic ammonia production.

Electrocatalytic oxidation of alcohols using heterogeneous catalysts is a promising aqueous, energy-efficient and environmentally friendly approach, especially for coupling different alcohols to prolong the carbon chain via co-oxidation. Precisely regulating critical steps to tailor electrode materials and electrolyte composition is key to selectively coupling alcohols for targeted synthesis. However, selectively coupling different alcohols remains challenging due to the lack of effective catalyst and electrolyte design promoting specific pathways. Herein, we demonstrate a paired electrolysis strategy for combining anodic oxidative coupling of ethanol (EtOH) and benzyl alcohol (PhCH2OH) to synthesize cinnamaldehyde (CAL) and cathodic ammonia production. The strategies involve: (i) utilizing the salt-out effect to balance selective oxidation and coupling rates; (ii) developing platinum-loaded nickel hydroxide electrocatalysts to accelerate intermediate coupling kinetics; (iii) introducing thermodynamically favorable nitrate reduction at the cathode to improve coupling selectivity by avoiding hydrogenation of products while generating valuable ammonia instead of hydrogen. We achieved 85% coupling selectivity and 278 µmol/h NH3 productive rate at 100 mA/cm2 with a low energy input (∼1.63 V). The membrane-free, low energy, scalable approach with a wide substrate scope highlights promising applications of this methodology. This work advances heterogeneous electrocatalytic synthesis through rational design principles that integrate anodic oxidative coupling with cathodic nitrate reduction reactions, having synergistic effects on efficiency and selectivity.

Spatially Confined Microcells: A Path toward TMD Catalyst Design.

With the ability to maximize the exposure of nearly all active sites to reactions, two-dimensional transition metal dichalcogenide (TMD) has become a fascinating new class of materials for electrocatalysis. Recently, electrochemical microcells have been developed, and their unique spatial-confined capability enables understanding of catalytic behaviors at a single material level, significantly promoting this field. This Review provides an overview of the recent progress in microcell-based TMD electrocatalyst studies. We first introduced the structural characteristics of TMD materials and discussed their site engineering strategies for electrocatalysis. Later, we comprehensively described two distinct types of microcells: the window-confined on-chip electrochemical microcell (OCEM) and the droplet-confined scanning electrochemical cell microscopy (SECCM). Their setups, working principles, and instrumentation were elucidated in detail, respectively. Furthermore, we summarized recent advances of OCEM and SECCM obtained in TMD catalysts, such as active site identification and imaging, site monitoring, modulation of charge injection and transport, and electrostatic field gating. Finally, we discussed the current challenges and provided personal perspectives on electrochemical microcell research.

Electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites for persistent uranium recovery at a low potential.

Electrochemical uranium extraction (EUE) from seawater is a very promising strategy, but its practical application is hindered by the high potential for electrochemical system, as well as the low selectivity, efficiency, and poor stability of electrode. Herein, we developed creatively a low potential strategy for persistent uranium recovery by electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites coupled with indirect reduction of uranium, finally achieving high selectivity, efficient and persistent uranium recovery. As-designed titanium dioxide rich in oxygen vacancies (TiO2-VO) electrode displayed an EUE efficiency of ∼99.9 % within 180 min at a low potential of 0.09 V in simulated seawater with uranium of 5∼20 ppm. Moreover, the TiO2-VO electrode also showed high selectivity (89.9 %) to uranium, long-term cycling stability and antifouling activity in natural seawater. The excellent EUE property was attributed to the fact that electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites enhanced EUE cycling process and achieved persistent uranium recovery. The continuous regeneration of oxygen vacancies not only reduced the adsorption energy of U(VI)O22+ but also serve as a storage and transportation channel for electrons, accelerating electron transfer from Ti(III) to U(VI) at solid-liquid interface and promoting EUE kinetic rate.

Electrocatalysis Boosts the Methanol Thermocatalytic Dehydrogenation for High-Purity H2 and CO Production.

Hydrogen production from methanol represents an energy-sustainable way to produce ethanol, but it normally results in heavy CO2 emissions. The selective conversion of methanol into H2 and valuable chemical feedstocks offers a promising strategy; however, it is limited by the harsh operating conditions and low conversion efficiency. Herein, we realize efficient high-purity H2 and CO production from methanol by coupling the thermocatalytic methanol dehydrogenation with electrocatalytic hydrogen oxidation on a bifunctional Ru/C catalyst. Electrocatalysis enables the acceleration of C-H cleavage and reduces the partial pressure of hydrogen at the anode, which drives the chemical equilibrium and significantly enhances methanol dehydrogenation. Furthermore, a bilayer Ru/C + Pd/C electrode is designed to mitigate CO poisoning and facilitate hydrogen oxidation. As a result, a high yield of H2 (558.54 mmol h-1 g-1) with high purity (99.9%) was achieved by integrating an applied cell voltage of 0.4 V at 200 °C, superior to the conventional thermal and electrocatalytic processes, and CO is the main product at the anode. This work presents a new avenue for efficient H2 production together with valuable chemical synthesis from methanol.

Lutetium-Induced Ultrafine PtRu Nanoclusters with a High Electrochemical Surface Area for Direct Methanol Fuel Cells at Alleviated Temperatures.

PtRu alloys have been recognized as the state-of-the-art catalysts for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, their applications in DMFCs are still less efficient in terms of both catalytic activity and durability. Rare earth (RE) metals have been recognized as attractive elements to tune the catalytic activity, while it is still a world-class challenge to synthesize well-dispersed Pt-RE alloys. Herein, we developed a novel hydrogen-assisted magnesiothermic reduction strategy to prepare a highly dispersed carbon-supported lutetium-doped PtRu catalyst with ultrafine nanoclusters and atomically dispersed Ru sites. The PtRuLu catalyst shows an outstanding high electrochemical surface area (ECSA) of 239.0 m2 gPt-1 and delivers an optimized MOR mass activity and specific activity of 632.5 mA mgPt-1 and 26 A cmPt-2 at 0.4 V vs saturated calomel electrode (SCE), which are 3.6 and 3.5 times of commercial PtRu-JM and an order higher than PtLu, respectively. These novel catalysts have been demonstrated in a high-temperature direct methanol fuel cell running in a temperature range of 180-240 °C, achieving a maximum power density of 314.3 mW cm-2. The AC-STEM imaging, in situ ATR-IR spectroscopy, and DFT calculations disclose that the high performance is resulted from the highly dispersed PtRuLu nanoclusters and the synergistic effect of the atomically dispersed Ru sites with PtRuLu nanoclusters, which significantly reduces the CO* intermediates coverage due to the promoted water activation to form the OH* to facilitate the CO* removal.

Ultra-Low-Potential Methanol Oxidation on Single-Ir-Atom Catalyst.

Methanol oxidation plays a central role to implement sustainable energy economy, which is restricted by the sluggish reaction kinetics due to the multi-electron transfer process accompanied by numerous sequential intermediate. In this study, an efficient cascade methanol oxidation reaction is catalyzed by single-Ir-atom catalyst at ultra-low potential (<0.1 V) with the promotion of the thermal and electrochemical integration in a high temperature polymer electrolyte membrane electrolyzer. At the elevated temperature, the electron deficient Ir site with higher methanol affinity could spontaneous catalyze the CH3OH dehydrogenation to CO under the voltage, then the generated CO and H2 was electrochemically oxidized to CO2 and proton. However, the methanol cannot thermally decompose with the voltage absence, which confirm the indispensable of the coupling of thermal and electrochemical integration for the methanol oxidation. By assembling the methanol oxidation reaction with hydrogen evolution reaction with single-Ir-atom catalysts in the anode chamber, a max hydrogen production rate reaches 18 mol gIr -1 h-1, which is much greater than that of Ir nanoparticles and commercial Pt/C. This study also demonstrated the electrochemical methanol oxidation activity of the single atom catalysts, which broadens the renewable energy devices and the catalyst design by an integration concept.

Photoelectrochemical Lithium Extraction from Waste Batteries.

The amount of global hybrid-electric and all electric vehicle has increased dramatically in just five years and reached an all-time high of over 10 million units in 2022. A good deal of waste lithium (Li)-containing batteries from dead vehicles are invaluable unconventional resources with high usage of Li. However, the recycle of Li by green approaches is extremely inefficient and rare from waste batteries, giving rise to severe environmental pollutions and huge squandering of resources. Thus, in this mini review, we briefly summarized a green and promising route-photoelectrochemical (PEC) technology for extracting the Li from the waste lithium-containing batteries. This review first focuses on the critical factors of PEC performance, including light harvesting, charge-carrier dynamics, and surface chemical reactions. Subsequently, the conventional and PEC technologies applying in the area of Li recovery processes are analyzed and discussed in depth, and the potential challenges and future perspective for rational and healthy development of PEC Li extraction are provided positively.

Pulse potential mediated selectivity for the electrocatalytic oxidation of glycerol to glyceric acid.

Preventing the deactivation of noble metal-based catalysts due to self-oxidation and poisonous adsorption is a significant challenge in organic electro-oxidation. In this study, we employ a pulsed potential electrolysis strategy for the selective electrocatalytic oxidation of glycerol to glyceric acid over a Pt-based catalyst. In situ Fourier-transform infrared spectroscopy, quasi-in situ X-ray photoelectron spectroscopy, and finite element simulations reveal that the pulsed potential could tailor the catalyst's oxidation and surface micro-environment. This prevents the overaccumulation of poisoning intermediate species and frees up active sites for the re-adsorption of OH adsorbate and glycerol. The pulsed potential electrolysis strategy results in a higher glyceric acid selectivity (81.8%) than constant-potential electrocatalysis with 0.7 VRHE (37.8%). This work offers an efficient strategy to mitigate the deactivation of noble metal-based electrocatalysts.

Catalyst Selection over an Electrochemical Reductive Coupling Reaction toward Direct Electrosynthesis of Oxime from NOx and Aldehyde.

Aqueous electrochemical coupling reactions, which enable the green synthesis of complex organic compounds, will be a crucial tool in synthetic chemistry. However, a lack of informed approaches for screening suitable catalysts is a major obstacle to its development. Here, we propose a pioneering electrochemical reductive coupling reaction toward direct electrosynthesis of oxime from NOx and aldehyde. Through integrating experimental and theoretical methods, we screen out the optimal catalyst, i.e., metal Fe catalyst, that facilitates the enrichment and C-N coupling of key reaction intermediates, all leading to high yields (e.g., ∼99% yield of benzaldoxime) for the direct electrosynthesis of oxime over Fe. With a divided flow reactor, we achieve a high benzaldoxime production of 22.8 g h-1 gcat-1 in ∼94% isolated yield. This work not only paves the way to the industrial mass production of oxime via electrosynthesis but also offers references for the catalyst selection of other electrochemical coupling reactions.

Construction of Ag─Co(OH)2 Tandem Heterogeneous Electrocatalyst Induced Aldehyde Oxidation and the Co-Activation of Reactants for Biomass Effective and Multi-Selective Upgrading.

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) provides a feasible way for utilization of biomass resources. However, how to regulate the selective synthesis of multiple value-added products is still a great challenge. The cobalt-based compound is a promising catalyst due to its direct and indirect oxidation properties, but its weak adsorption capacity restricts its further development. Herein, by constructing Ag─Co(OH)2 heterogeneous catalyst, the efficient and selective synthesis of 5-hydroxymethyl-2-furanoic acid (HMFCA) and 2,5-furan dicarboxylic acid (FDCA) at different potential ranges are realized. Based on various physical characterizations, electrochemical measurements, and density functional theory calculations, it is proved that the addition of Ag can effectively promote the oxidation of aldehyde group to a carboxyl group, and then generate HMFCA at low potential. Moreover, the introduction of Ag can activate cobalt-based compounds, thus strengthening the adsorption of organic molecules and OH- species, and promoting the formation of FDCA. This work achieves the selective synthesis of two value-added chemicals by one tandem catalyst and deeply analyzes the adsorption enhancement mechanism of the catalyst, which provides a powerful guidance for the development of efficient heterogeneous catalysts.

Enhanced charge-carrier dynamics and efficient solar-to-urea conversion on Si-based photocathodes.

Photoelectrochemical (PEC) coupling of CO2 and nitrate can provide a useful and green source of urea, but the process is affected by the photocathodes with poor charge-carrier dynamics and low conversion efficiency. Here, a NiFe diatomic catalysts/TiO2 layer/nanostructured n+p-Si photocathode is rationally designed, achieving a good charge-separation efficiency of 78.8% and charge-injection efficiency of 56.9% in the process of PEC urea synthesis. Compared with the electrocatalytic urea synthesis by using the same catalysts, the Si-based photocathode shows a similar urea yield rate (81.1 mg·h-1·cm-2) with a higher faradic efficiency (24.2%, almost twice than the electrocatalysis) at a lower applied potential under 1 sun illumination, meaning that a lower energy-consumption method acquires more aimed productions. Integrating the PEC measurements and characterization results, the synergistic effect of hierarchical structure is the dominating factor for enhancing the charge-carrier separation, transfer, and injection by the matched band structure and favorable electron-migration channels. This work provides a direct and efficient route of solar-to-urea conversion.

Tip-like Fe-N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction.

Single atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O2 electroreduction. Here, enriched tip-like FeN4 sites (T-Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip-like FeN4 and the more denser interfacial water layer, thereby enhancing the kinetics of the proton-coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip-like FeN4 sites, promoting the dissociation of O-O bond via side-on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T-Fe SAC nanoreactor exhibits excellent ORR activities (E1/2 =0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN4 and Pt/C. This work clarified the in-depth insights into the origin of catalytic activity of tip-like FeN4 sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.

Catalysts and electrolyzers for the electrochemical CO2 reduction reaction: from laboratory to industrial applications.

To cope with the urgent environmental pressure and tight energy demand, using electrocatalytic methods to drive the reduction of carbon dioxide molecules and produce a variety of fuels and chemicals, is one of the effective pathways to achieve carbon neutrality. In recent years, many significant advances in the study of the electrochemical carbon dioxide reduction reaction (CO2RR) have been made, but most of the works exhibit low current density, small electrode area and poor long-term stability, which are not suitable for large-scale industrial applications. Herein, combining the research achievements obtained in laboratories and the practical demand of industrial production, we summarize recent frontier progress in the field of the electrochemical CO2RR, including the fundamentals of catalytic reactions, catalyst design and preparation, and the construction of electrolyzers. In addition, we discuss the bottleneck problem of industrial CO2 electrolysis, and further present the prospect of the essential issues to be solved by the available technology for industrial electrolysis. This review can provide some basic understanding and knowledge accumulation for the development and practical application of electrochemical CO2RR technology.

Vacancy-induced catalytic mechanism for alcohol electrooxidation on nickel-based electrocatalyst.

Owing to outstanding performances, nickel-based electrocatalysts are commonly used in electrochemical alcohol oxidation reactions (AORs), and the active phase is usually vacancy-rich nickel oxide/hydroxide (NiOx Hy ) species. However, researchers are not aware of the catalytic role of atom vacancy in AORs. Here, we study vacancy-induced catalytic mechanisms for AORs on NiOx Hy species. As to AORs on oxygen-vacancy-poor ß-Ni(OH)2 , the only redox mediator is electrooxidation-induced electrophilic lattice oxygen species, which can only catalyze the dehydrogenation process (e.g., the electrooxidation of primary alcohol to carboxylic acid) instead of the C-C bond cleavage. Hence, vicinal diol electrooxidation reaction involving the C-C bond cleavage is not feasible with oxygen-vacancy-poor ß-Ni(OH)2 . Only through oxygen vacancy-induced adsorbed oxygen-mediated mechanism, can oxygen-vacancy-rich NiOx Hy species catalyze the electrooxidation of vicinal diol to carboxylic acid and formic acid accompanied with the C-C bond cleavage. Crucially, we examine how vacancies and vacancy-induced catalytic mechanisms work during AORs on NiOx Hy species.

A Universal Approach for Sustainable Urea Synthesis via Intermediate Assembly at the Electrode/Electrolyte Interface.

Electrocatalytic C-N coupling process is indeed a sustainable alternative for direct urea synthesis and co-upgrading of carbon dioxide and nitrate wastes. However, the main challenge lies in the unactivated C-N coupling process. Here, we proposed a strategy of intermediate assembly with alkali metal cations to activate C-N coupling at the electrode/electrolyte interface. Urea synthesis activity follows the trend of Li+

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.

Selective Electroreduction of 5-Hydroxymethylfurfural to Dimethylfuran in Neutral Electrolytes via Hydrogen Spillover and Adsorption Configuration Adjustment.

5-Hydroxymethylfurfural (HMF), one of the essential C6 biomass derivatives, has been deeply investigated in electrocatalytic reduction upgrading. Nevertheless, the high product selectivity and rational design strategy of electrocatalysts for electrocatalytic HMF reduction is still a challenge. Here, a high selective electro-reduction of HMF to dimethylfuran (DMF) on palladium (Pd) single atom loaded on titanium dioxide (Pd SA/TiO2 ) via hydrogen spillover and adsorption configuration adjustment in neutral electrolytes is achieved. Combining density functional theory calculations and in situ characterization, it is revealed that Pd single atom could weaken the interaction between Pd atoms and adsorbed hydrogen (*H) to promote the *H spillover for increasing *H coverage on the surface and maintain the tilted adsorption configuration to activate C═O bond; thus the selectivity of DMF on Pd SA/TiO2 increases to 90.33%. Besides, it is elaborated that low *H coverage on TiO2 favors the formation of bis(hydroxymethyl)hydro-furoin (BHH), and the flat adsorption configuration of HMF on Pd nanoparticles benefits to form 2,5-dihydroxymethylfuran (DHMF). This work provides a promising approach for modifying electrocatalysts to realize the selective electroreduction of HMF to value-added products.

Cu@Co with Dilatation Strain for High-Performance Electrocatalytic Reduction of Low-Concentration Nitric Oxide.

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3 ) is a clean and sustainable strategy to simultaneously remove NO and synthesize NH3 . However, the conversion of low concentration NO to NH3 is still a huge challenge. In this work, the dilatation strain between Cu and Co interface over Cu@Co catalyst is built up and investigated for electroreduction of low concentration NO (volume ratio of 1%) to NH3 . The catalyst shows a high NH3 yield of 627.20 µg h-1 cm-2 and a Faradaic efficiency of 76.54%. Through the combination of spherical aberration-corrected transmission electron microscopy and geometric phase analyses, it shows that Co atoms occupy Cu lattice sites to form dilatation strain in the xy direction within Co region. Further density functional theory calculations and NO temperature-programmed desorption (NO-TPD) results show that the surface dilatation strain on Cu@Co is helpful to enhance the NO adsorption and reduce energy barrier of the rate-determining step (*NO to *NOH), thereby accelerating the catalytic reaction. To simultaneously realize NO exhaust gas removal, NH3 green synthesis, and electricity output, a Zn-NO battery with Cu@Co cathode is assembled with a power density of 3.08 mW cm-2 and an NH3 yield of 273.37 µg h-1 cm-2 .