Local Alkaline Research Articles

Microenvironment regulation for high-performance acidic CO2 electroreduction on Poly(ionic liquid)-modified Cu surface

Electrocatalytic reduction of CO2 (CO2RR) under acidic conditions provides a feasible way for converting CO2 to multi-carbon products (C2+) with high feedstock conversion and high energetic efficiency (EE). In this work, poly(ionic liquid) (PIL)-Cu hybrids were employed as excellent acidic CO2RR electrocatalysts. A high faradaic efficiency towards C2+ products (FEC2+) of more than 61.0 % was achieved within a wide pH range from 2 to 14 at –700 mA cm–2. The optimum FEC2+ of 83.1 % was obtained at –700 mA cm–2 and pH = 2, corresponding to an EEC2+ of 37.6 %. By reducing the inlet CO2 flow rate to 1.59 mL min–1, a very high CO2 single-pass conversion of 98.7 % was achieved at –300 mA cm–2. The confinement of PIL layer caused by the semi-rigid abundant porous structure and dense cationic-anionic network enables the maintenance of a moderate local alkaline microenvironment and enrichment of K+ cations at the active sites. These effects jointly promote the C–C coupling at the Cu-PIL interface under acidic conditions. Remarkably, the CO2RR pathway can be regulated by functionality and morphology of the PIL layer.

Exudate Unidirectional Pump to Promote Glucose Catabolism Triggering Fenton-Like Reaction for Chronic Diabetic Wounds Therapy.

The massive accumulation of exudate containing high concentrations of glucose causes wound infection and triggers the release of inflammatory factors, which in turn delays the closure of diabetic wounds. In this study, a Janus membrane is constructed by combining glucose oxidase (GOx) and copper ions (Cu2+) for the treatment of diabetic wounds, which is named as Janus@GOx/Cu2+. It consists of hydrophobic, transitional, and superhydrophilic layers in a three-layer structure with gradient hydrophilicity for self-pumping properties. The Janus@GOx/Cu2+ membrane triggers a series of cascading reactions while pumping out diabetic wound exudates. First, glucose oxidase loaded onto the hydrophilic layer of the Janus@GOx/Cu2+ membrane decomposes glucose into hydrogen peroxide (H2O2) and glucuronic acid, reducing the local glucose level. The generated glucuronic acid neutralizes the local alkaline environment of chronic wounds. Simultaneously, the H2O2 interacts with the Cu2+ contained in the hydrophobic layers of the Janus@GOx/Cu2+ membrane via a Fenton-like reaction, generating hydroxyl radicals with excellent bactericidal properties. Cu2+ promotes angiogenesis and wound healing in diabetic wounds. Under the action of multiple responses, the Janus@GOx/Cu2+ membrane promotes wound healing in diabetic infections.

Constructing alkaline microenvironment on catalyst surface for enhanced electrocatalytic synthesis of hydrogen peroxide in a neutral electrolyte

The direct electrochemical synthesis of H2O2 via a two-electron oxygen reduction reaction (2e− ORR) offers a feasible alternative to the energy-intensive anthraquinone oxidation process. Compared to alkaline electrolytes, challenges remain in achieving high 2e− ORR selectivity and activity for electrosynthesis of H2O2 in neutral electrolytes due to the low concentration of OH−, which hinders the effective binding of key intermediate OOH*. Here, we introduced Lewis acid TiO2 to modify carbon black catalyst for adsorbing in-situ generated OH− and created a local alkaline microenvironment for enhancing the 2e− ORR activity and selectivity in neutral electrolytes. H2O2 productivity of TiO2 modified carbon black catalyst (52.5 mmol L−1 h−1) in a neutral electrolyte (0.5 M Na2SO4) at 0.2 V vs. RHE was 1.6 times as much as that of pristine carbon black (33 mmol L−1 h−1), which was similar with that of pristine carbon black (58.4 mmol L−1 h−1) in an alkaline electrolyte (0.1 M KOH). The finite-element method simulations and experiments indicated that TiO2 could enhance local alkalinity to increase the current density for facilitating 2e− ORR. The density functional theory calculations indicated that the introducing of TiO2 into the CB structure could promote the adsorption of O2, facilitate the adsorption of *OOH and reduce the overpotential, resulting in high activity towards 2e− ORR to H2O2. This work proposes a new strategy for optimizing electrode–electrolyte interface to enhance 2e− ORR performance in neutral electrolytes.

In-Situ Near Crack Tip pH Measurements to Confirm Alkaline Crack Conditions Causing Crack Arrest in Cathodically Polarized AA5456-H116

ABSTRACT In-situ crack tip pH measurements for corrosion fatigue (CF) cracks in sensitized AA5456-H116 loaded under low loading frequencies show that cathodic polarization has the ability to arrest actively growing stress corrosion (SCC) and CF cracks and produce a local alkaline crack tip pH. A method for measuring crack tip pH in-situ was developed. For AA5456-H116 under a single level of high sensitization, CF experiments while loading in the Paris regime at a loading frequency of 0.1 Hz were conducted under freely corroding conditions and a cathodic polarization of −1.3 VSCE. Results show that under freely corroding conditions the crack actively grows, and the crack tip pH is slightly acidic, while at −1.3 VSCE an alkaline crack tip develops with a pH of 10-12. The findings of this study support the earlier published hypothesis that crack arrest of SCC and low loading frequency CF cracks is due to corrosion-induced blunting after the development of highly alkaline conditions that causes corrosion of the crack tip region blunting and halting the crack.

Ag–Cr2O3 interfaces with local alkaline microenvironments for electroreduction of CO2 to CO in an acidic electrolyte

Electrochemical CO2 reduction in acidic electrolyte is a potential strategy for efficient CO2 utilization by preventing the formation of carbonate, but it remains a great challenge to improve the selectivity of CO2 reduction in acidic electrolytes due to the competitive hydrogen evolution reaction. Herein, we demonstrate Ag2CrO4 derived Ag–Cr2O3 composite catalyst with local alkaline microenvironments for enhanced selectivity of CO2 to CO product in an acidic KCl electrolyte. Under the electrochemical reduction of CO2, the Ag2CrO4 pre-catalyst undergoes a chemical transformation induced by chloride ions to generate AgCl–Cr2O3, meanwhile, AgCl is electrochemically reduced Ag to form a Cr2O3 coated Ag composite catalyst with rich Ag–Cr2O3 interfaces. The Ag–Cr2O3 gas diffusion electrode constructed from carbon nanopowder effectively increases the hydrophobicity of the electrode, and the optimized electrode exhibits high CO Faradaic efficiency (FE) (over 75%) at a wide current density of 50–300 mA cm-2 and achieves a maximum FE of 86.7% toward CO product at 300 mA cm-2. The in situ Raman spectroscopy reveals that Cr2O3 can adsorb OH− which regulates the local alkaline environment to promote the CO2 adsorption on the Ag–Cr2O3 interface and stabilize the *CO2-/*COOH intermediates in the acidic electrolyte. This work provides an effective strategy to tune the reaction interfaces for CO2 reduction in acidic electrolytes.

Influence of Chloride Ion Concentration on Corrosion Behavior of WC–MgO Composite

The influence of chloride ion (Cl−) concentration on the corrosion mechanism of WC–MgO composites has been studied in this work. The results suggest that the corrosion resistance of WC–MgO composite decreases first and then increases with the increase in Cl− concentration. Solution conductivity and dissolved oxygen content are the main influence factors. The solution conductivity determines the charge transfer process, and the dissolved oxygen determines the cathodic oxygen absorption reaction. The corrosion characteristic is typical pitting corrosion. Meanwhile, the corrosion mechanism contains an oxidation process of the WC matrix and the dissolution destruction of the MgO toughening phase. The formation of the WO3 corrosion layer hinders the general corrosion to protect the inner material. However, the dissolution of MgO induces the initiation of pitting. The local alkaline caused by MgO dissolution promotes the dissolution of the WC matrix, which leads to the expansion of pitting.

Reactive Microneedle Patches with Antibacterial and Dead Bacteria-Trapping Abilities for Skin Infection Treatment.

Bacterial skin infections are highly prevalent and pose a significant public health threat. Current strategies are primarily focused on the inhibition of bacterial activation while disregarding the excessive inflammation induced by dead bacteria remaining in the body and the effect of the acidic microenvironment during therapy. In this study, a novel dual-functional MgB2 microparticles integrated microneedle (MgB2 MN) patch is presented to kill bacteria and eliminate dead bacteria for skin infection management. The MgB2 microparticles not only can produce a local alkaline microenvironment to promote the proliferation and migration of fibroblasts and keratinocytes, but also achieve >5 log bacterial inactivation. Besides, the MgB2 microparticles effectively mitigate dead bacteria-induced inflammation through interaction with lipopolysaccharide (LPS). With the incorporation of these MgB2 microparticles, the resultant MgB2 MN patches effectively kill bacteria and capture dead bacteria, thereby mitigating these bacteria-induced inflammation. Therefore, the MgB2 MN patches show good therapeutic efficacy in managing animal bacterial skin infections, including abscesses and wounds. These results indicate that reactive metal borides-integrated microneedle patches hold great promise for the treatment of clinical skin infections.

Local Warm Alkaline Hydrogen Peroxide Solutions and Targeted Temperature Management Improve the Treatment of Chronic Wounds

Introduction: To date, there is no systematic review of the effect of local hypo-, normo- and hyperthermia on the processes of local interaction of antiseptics with dense biological masses covering the surface of chronic wounds. Accelerated and reliable cleansing of the wound surface from purulent masses still remains an unsolved problem of surgery. Methods: 6 inventions were found from beginning to 1986 in databases such as EAPATIS, BYPATENTS, DWPI, DEPATISnet, PATENTSCOPE, Espacenet, RUPTO, USPTO, CIPO, CNIPA, KIPRIS, PatSearch, J-PlatPat, Google Patents and TPO. Due to the small number of inventions, methodological heterogeneity, and differences in the content of their claims, a quantitative meta-analysis could not be performed. Results: The prospects of innovative proposals on the influence of local hypothermia and local hyperthermia on the process of local interaction of antiseptic drug solutions with purulent masses and blood on the surface of chronic wounds have been analyzed. The results of the included studies were presented only qualitatively (descriptively). Conclusion: The first review of inventions presents formulations of invented drugs created by physicochemical repurposing of hydrogen peroxide from antiseptic to pyolytics, mucolytics, hemolytics, expectorants and oxygen-releasing antihypoxants. Warm alkaline hydrogen peroxide solutions (WAHPSs) have been shown to rapidly and reliably dissolve thick purulent masses, blood clots and dried blood spots, turning them into a lush oxygenating foam. Temperature regimes that optimize the sanitizing and washing action of WAHPSs in the treatment of chronic wounds and accelerate hemostasis in parenchymatous bleeding are specified.

Sustainable Aqueous Batteries Based on Bipolar Dissociation of Aluminum Hydroxyacetate Electrolyte.

Rechargeable aqueous batteries are potential systems for large-scale energy storage due to their high safety and low cost. However, developing aqueous batteries with high sustainability, affordability, and reversibility is urgent and challenging. Here we report an amphoteric aluminum hydroxyacetate (AlAc(OH)2) electrolyte with the ability of bipolar ionization of H+ and OH-, which facilitates the redox reactions at both the anthraquinone (AQ) anode and nickel hydroxide (Ni(OH)2) cathode. The bipolar ionization ability of the AlAc(OH)2(H2O)3 solvation structure results from the strong polarization ability of Al3+ and OH-. The H+/OH- dissociation ability with a dissociation constant of 5.0/3.0 is stronger than that of water (14.0), which boosts the simultaneous stable redox reactions of electrodes. Specifically, H+ uptake prevents the AQ anode from the formation of an ionic bond, suppressing the electrode dissolution, whereas OH- provides the local alkaline environment for the stable conversion reaction of the Ni(OH)2 cathode. The AQ anode in the designed AQ||Ni(OH)2 battery delivers a discharge capacity of 243.9 mAh g-1 and a capacity retention of 78.2% after 300 cycles with high reversibility. Moreover, a pouch cell with a discharge capacity of 0.90 Ah was assembled, exhibiting an energy density of 44.7 Wh kg-1 based on the total mass of the battery. This work significantly widens the types of aqueous batteries and represents a design philosophy of bipolar electrolytes and distinct electrochemical reactions with H+ and OH-.

Acetamide Electrosynthesis from CO2 and Nitrite in Water.

Renewable electricity driven electrocatalytic CO2 reduction reaction (CO2 RR) is a promising solution to carbon neutralization, which mainly generate simple carbon products. It is of great importance to produce more valuable C-N chemicals from CO2 and nitrogen species. However, it is challenging to co-reduce CO2 and NO3 - /NO2 - to generate aldoxime an important intermediate in the electrocatalytic C-N coupling process. Herein, we report the successful electrochemical conversion of CO2 and NO2 - to acetamide for the first time over copper catalysts under alkaline condition through a gas diffusion electrode. Operando spectroelectrochemical characterizations and DFT calculations, suggest acetaldehyde and hydroxylamine identified as key intermediates undergo a nucleophilic addition reaction to produce acetaldoxime, which is then dehydrated to acetonitrile and followed by hydrolysis to give acetamide under highly local alkaline environment and electric field. Moreover, the above mechanism was successfully extended to the formation of phenylacetamide. This study provides a new strategy to synthesize highly valued amides from CO2 and wastewater.

Acetamide Electrosynthesis from CO2 and Nitrite in Water

AbstractRenewable electricity driven electrocatalytic CO2 reduction reaction (CO2RR) is a promising solution to carbon neutralization, which mainly generate simple carbon products. It is of great importance to produce more valuable C−N chemicals from CO2 and nitrogen species. However, it is challenging to co‐reduce CO2 and NO3−/NO2− to generate aldoxime an important intermediate in the electrocatalytic C−N coupling process. Herein, we report the successful electrochemical conversion of CO2 and NO2− to acetamide for the first time over copper catalysts under alkaline condition through a gas diffusion electrode. Operando spectroelectrochemical characterizations and DFT calculations, suggest acetaldehyde and hydroxylamine identified as key intermediates undergo a nucleophilic addition reaction to produce acetaldoxime, which is then dehydrated to acetonitrile and followed by hydrolysis to give acetamide under highly local alkaline environment and electric field. Moreover, the above mechanism was successfully extended to the formation of phenylacetamide. This study provides a new strategy to synthesize highly valued amides from CO2 and wastewater.

Pure-water-fed, electrocatalytic CO2 reduction to ethylene beyond 1,000 h stability at 10 A

AbstractElectrocatalytic CO2 reduction at near-ambient temperatures requires a complex inventory of protons, hydroxyls, carbonate ions and alkali-metal ions at the cathode and anode to be managed, necessitating the use of ion-selective membranes to regulate pH. Anion-exchange membranes provide an alkaline environment, allowing CO2 reduction at low cell voltages and suppression of hydrogen evolution while maintaining high conversion efficiencies. However, the local alkaline conditions and the presence of alkali cations lead to problematic carbonate formation and even precipitation. Here we report a pure-water-fed (alkali-cation-free) membrane–electrode–assembly system for CO2 reduction to ethylene by integrating an anion-exchange membrane and a proton-exchange membrane at the cathode and anode side, respectively, under forward bias. This system effectively suppresses carbonate formation and prevents salt precipitation. A scaled-up electrolyser stack achieved over 1,000 h stability without CO2 and electrolyte losses and with 50% Faradaic efficiency towards ethylene at a total current of 10 A.

Corrosion sensing and self-healing composite coatings on magnesium alloy AZ31 enabled by stimuli-responsive microcapsules loaded with phenolphthalein and epoxy resin

Polymer coatings inevitably suffer from micro-damage during film formation and the in-service period, leading to interfacial corrosion of the metal substrate and even catastrophic accidents. Constructing a coating system that integrates early corrosion sensing and efficient damage self-healing capabilities is highly pursued yet difficult to achieve in practice. This work reports a strategy for designing smart anticorrosion coating with autonomous corrosion-detecting and in-situ self-healing functions. The dual-functional composeite coating was designed on magnesium (Mg) alloy AZ31, via embedding urea-formaldehyde microcapsules loaded with phenolphthalein (PhPh)/epoxy resin. By immersing the scribed samples in a 3.5 wt% NaCl solution, the interfacial corrosion reaction at coating damage can be timely sensed and visualized by the apparent pink color in just 7 min. The local alkaline environment produced by Mg corrosion, initiates the chromogenic reaction of PhPh and indicates interfacial corrosion. Meanwhile, the released epoxy resin, as a healing agent can effectively fill the coating defects and thus prevent the intrusion of corrosive medium. Electrochemical impedance spectroscopy shows that the long-term corrosion resistance of the coating was significantly improved after introducing synthesized microcapsules. After 115 d of immersion, the low-frequency impedance of the composite coating with 3 wt% of microcapsules (PUM3) is above 1010 Ω·cm2, whereas the pure polyurea coating (PUA) has dropped to 109 Ω·cm2.This feasible and effective design concept of microcapsule-based intelligent anticorrosive coating provides a new idea for developing environmentally adaptive protective materials with corrosion sensing and self-healing functions.

Laboratory Investigation on Enhanced Oil Recovery Using Local Alkaline –Polymer for Niger – Delta Region

Approximately sixty percent of crude oil still lay trapped in the reservoir even after primary and secondary recovery processes have been completed, hence the need for a method that further improves recovery. To increase oil recovery and encourage utilization of local content, locally source alkaline and polymer materials were used to improve oil recovery in this study. The local alkaline and polymer used are plantain peel ash and corn starch respectively. The efficiency of the plantain peel ash and corn starch solution were tested using different seven core samples. The core samples were individually flooded with brine (salt and water) for secondary recovery process and different concentrations of plantain peel ash and corn starch both in stand-alone and in combined form were used for tertiary recovery. The results obtained from the experimental work showed that sample-B5 with 0.2g of plantain peel ash and 0.2g of corn starch in 100ml of brine gave the highest cumulative recovery of 86% as to compare to samples B1 and B2 which has the cumulative recovery of 70% and 78% respectively. Sample-B7 which has the highest concentration of corn starch (0.4g/100ml) gave the lowest recovery of 65% due to polymer adsorption on the rock surfaces which alters the rock wettability. The assessment of formation damage was done by evaluating and determining the permeability change after tertiary flooding. The concentrations with plantain peel ash have reduced permeability change. These locally sourced materials can replace synthetic enhanced oil recovery (EOR) chemical when properly modified and refined, and they are also cheap and environmentally friendly.

Elucidating key mechanistic processes during acidic CO2 electroreduction on gas diffusion electrodes towards stable production of formic acid

The electrochemical reduction of CO2 using renewable electricity could be a sustainable alternative to produce formic acid. Although using bulk acidic electrolyte offers system and downstream processing benefits, neutral to alkaline electrolyte systems prevail due to challenge suppressing hydrogen evolution in acidic environment. In recent years, it has been shown that HER could be mitigated by confining the OH- being generated and constraining the movement of H3O+ towards reaction surface, thereby producing an alkaline reaction environment within the electrode. Herein, we have demonstrated how a porous and highly hydrophobic Bi-based gas diffusion electrode enables remarkably efficient bulk acidic electrolysis. Importantly, the local alkaline reaction environment has been proven via electrochemical impedance spectroscopy and pH visualization. Furthermore, optical monitoring of electrolyte conditions through a transparent cell sheds light on the CO2 recovery process in the acidic system, promoting a better technical practice in handling with electrochemical cells and CO2 recirculation. Finally, HCOOH accumulation as the key degradation reason is unveiled through investigation into the impact of operating modes on the stability at high current density, where earlier studies failed to adequately address. It is believed that this valuable insight could facilitate stable and efficient formic acid production in future work.

Effect of unsoluble corrosion products of WE43 alloys in vitro on macrophages.

Magnesium alloys have been used to manufacture biodegradable implants, bone graft substitutes, and cardiovascular stents. WE43 was the most widely used magnesium alloy. The degradation process begins when the magnesium alloy stent is implanted in the body and comes into contact with body fluid. The degradation products include hydrogen, Mg2+ , local alkaline environment, and unsoluble products. A large number of studies focused on Mg2+ and pH in vitro, and in vivo of magnesium alloys, but few studies on unsoluble corrosion products (UCPs). In this study, UCPs of WE43 alloy were prepared by immersion in vitro, and their effects on macrophages were investigated. The results showed that the unsoluble corrosion products were Mg24Y5, Mg12YNd, and MgCO3 ·3H2 O, which were dose-dependent on the apoptosis and necrosis of macrophages. After phagocytosis of UCPs, macrophages mainly metabolize in lysosome, and autophagy also participates in the metabolism of UCPs. It also decreases mitochondrial membrane potential and increases lysosomes, endoplasmic reticulum stress, and P2X7 receptor activation. These will increase reactive oxygen species (ROS) in cells, activating NLRP3 inflammatory corpuscles, activating the downstream pro-IL18 and pro-IL1β, and converting it to IL-18, and IL-1β. However, its pro-inflammatory effect is far lower than that of the classical Lipopolysaccharide (LPS) pro-inflammatory pathway. This work has increased our understanding of magnesium alloy metabolism and provides new ideas for the clinical application of magnesium alloys.

Mn‐Precipitates Found in a Martian Crustal Rock

AbstractAlteration minerals in one of the Martian meteorite nakhlites, Yamato (Y) 000802, were studied to understand the alteration process and conditions. Mn‐precipitates are discovered between altered plagioclase grains in Y 000802. Mn‐precipitates consist of hausmannite (), manganite (γ‐Mn3+OOH), rhodochrosite (Mn2+CO3), and a trace amount of Mn4+O2 mineral. Jarosite ) is also found. Mn2+ dissolved from olivine contributes to the formation of Mn‐precipitates. A weakly acidic‐neutral fluid containing a trace amount of altered the olivine, and Mn2+ was dissolved into the fluid. The fluid also reacted with plagioclase and probably induced dealkalization of plagioclase, causing a local strong alkaline environment. Plagioclase was altered to ferroan saponite‐nontronite + amorphous SiO2 under alkaline conditions. Simultaneously, Mn2+/3+‐precipitates were formed from the Mn2+‐containing fluid in the interstices between the altered plagioclase grains under the strong alkaline reducing environment. These alterations occurred in the deep part of the nakhlite body, where they are isolated from Martian subsurface water, including strong oxidants. The formation of Mn2+/3+‐precipitates may have been triggered by the melting of permafrost caused by an impact event around ∼633 Ma. Later, the nakhlite body was probably excavated by another impact, making it susceptible to water including strong oxidants. Pyrrhotite was dissolved and a highly acidic oxidizing fluid was formed, which would induce the formation of jarosite and the Mn4+O2 mineral between ∼633 Ma and ∼11 Ma.

Ab Initio Molecular Dynamics Study of the Proton Transfer in Hydroxyl Ion-Induced Hydrolysis of Aluminum Monomers.

The hydrolysis process of Al(H2O)63+ induced by hydroxyl ions (OH-) is significant to aluminum solution chemistry. Previous investigations of hydrolysis reactions have primarily relied on static calculations in an implicit solvent environment. Herein, we employ ab initio molecular dynamics (AIMD) to investigate the evolution process of Al(H2O)63+ under various local alkaline conditions in an explicit solvent environment. Our work demonstrates the effect of solvent water in hydrolysis reactions. Specifically, the stepwise hydrolysis reaction induced by hydroxyl ions involves water wire compression and concerted proton transfers. Dehydration reactions occur when the number of hydroxyl ligands attached to the aluminum ion (Al3+) equals or exceeds three. Moreover, the Al(H2O)n(OH)3 species exhibit unique hydrolysis and dehydration reaction characteristics compared to other species. The geometrically stable aluminum monomers determined by AIMD are Al(H2O)5(OH)12+, Al(H2O)4(OH)2+, Al(H2O)1(OH)3, and Al(OH)4-. In addition, the topological analysis analyzes the interaction between Al3+ and coordinated H2O in different configurations, indicating the weakest interaction appearing in Al(H2O)n(OH)3 species.

Mechanical, physical, and degradation properties of 3D printed PLA + Mg composites

In the present study, composite filaments were produced by PLA with and without 1 wt% Mg particles. DSC results show that the presence of Mg reduces the crystallinity and increases the melting temperature. Extruded filaments were used to produce tensile samples by 3D printing. The mechanical properties of 3D printed samples were compared with monolithic and micro-sized samples. The monolithic samples show inferior strength and ductility compared to 3D-printed samples, which feature aligned polymer chains. The micro-sized samples show superior mechanical properties compared to the large samples by having fewer potential failure points. 3D-printed samples were also produced by various infill orientations (0o, 45o, ±45o, and 90o), and the samples were tested for biodegradation in SBF solution. The 0o, infill orientation presented the highest mechanical properties before and after the immersion test. The 90o infill orientation samples were the most damaged samples by degradation. Microstructure studies show crevice corrosion is responsible for severe damage to the 90o infill orientation samples. Mg in the crevice forms and locks a local alkaline environment, accelerating degradation.

Spectroelectrochemical Investigation of the Local Alkaline Environment on the Surface-Nanostructured Au for the Conversion of CO2 to CO

The electrocatalytic conversion of carbon dioxide (CO2) into fuels could potentially achieve a sustainable carbon-based economy. The engineering of nanostructured metal electrodes can enhance their activity and selectivity by controlling their local chemical environment; however, direct observation is challenging. In this study, we investigate the molecular-level reaction mechanism of a nanoporous-structured Au electrode for the conversion of CO2 to carbon monoxide (CO) using surface-enhanced infrared absorption spectroscopy (SEIRAS). We designed a well-structured nanoporous Au layer (with a depth distribution of 56.3 nm) on a Si prism using a high-temperature non-aqueous anodization process and characterized the nanoporous Au electrode using atomic force microscopy (AFM) and X-ray absorption spectroscopy (XAS). The in situ SEIRAS results demonstrated that the nanoporous Au electrode has a dominant active site, promoting the linear CO intermediate and suppressing the bridging CO intermediate when compared with the non-structured Au electrode. We also revealed a high local pH at a reaction potential of −0.9 V and the slow diffusion kinetics of local CO32– at an open-circuit potential. These findings provide deeper insights into the electrochemical kinetics and corresponding mechanisms occurring in the electric double layers and highlight the potential for the design of efficient electrocatalysts for CO2 reduction.