High Local pH Research Articles

Production of C3–C6 Acetate Esters via CO Electroreduction in a Membrane Electrode Assembly Cell

AbstractElectrocatalytic carbon monoxide reduction has been previously reported to yield a range of carbonaceous products including alcohols, hydrocarbons and carboxylic acids. However, esters, an important family of organic compounds, have not been formed. Herein, we report the electrosynthesis of C3 to C6 acetate esters (H3C−(C=O)−O−R) from carbon monoxide using copper catalysts in a membrane electrode assembly cell. Ethyl acetate and propyl acetate could be produced with an unprecedented total Faradaic efficiency (FE) of ∼22 % and with a current density of up to −55 mA cm−2, alongside minor quantities of methyl acetate and butyl acetate. The esters are produced via the addition reaction of ethenone (H2C=C=O) and alcohols produced during CO reduction. We show that the near water‐free reaction conditions and the high local pH play key roles in the formation of the esters.

Three-Phases Interface Induced Local Alkalinity Generation Enables Electrocatalytic Glucose Oxidation in Neutral Electrolyte.

Electrocatalytic glucose oxidation is crucial to the development of non-enzymatic sensors, an attractive alternative for enzymatic biosensors. However, due to OH− consumption during the catalytic process, non-enzymatic detection generally requires electrolytes having an alkaline pH value, limiting its practical application since biofluids are neutral. Herein, via interfacial microenvironment design, we addressed this limitation by developing a non-enzymatic sensor with an air–solid–liquid triphase interface electrodes that synergistically integrates the functions of local alkalinity generation and electrocatalytic glucose oxidation. A sufficiently high local pH value was achieved via oxygen reduction reaction at the triphase interface, which consequently enabled the electrochemical oxidation (detection) of glucose in neutral solution. Moreover, we found that the linear detection range and sensitivity of triphase non-enzymatic sensor can be tuned by changing the electrocatalysts of the detection electrode. The triphase electrode architecture provides a new platform for further exploration and promotes practical application of non-enzymatic sensors.

Selective Borohydride Oxidation Reaction on Nickel Catalyst with Anion and Cation Exchange Ionomer for High‐Performance Direct Borohydride Fuel Cells

AbstractDirect borohydride fuel cells (DBFCs) operate with liquid H2O2 and a high‐energy‐density NaBH4 solution. A facile, direct synthesis method using a non‐noble nickel catalyst for the DBFC anode is shown. The complex anode reaction with an anion‐exchange ionomer (AEI) and a cation‐exchange ionomer (CEI) is evaluated in half‐cell and single‐cell configurations. The ionomer type produces high (AEI) or low local pH (CEI) at the active site of the catalyst in the single‐cell configuration, generating different catalytic reactions. The performance of the nickel catalyst is compared to that of a palladium catalyst. The selective catalytic activities for the borohydride oxidation reaction and hydrogen oxidation reaction are the key parameters for achieving good performance. Furthermore, fuel utilization and H2 evolution measurement in a single‐cell configuration provide more information on the complex anode reaction in the DBFC. The nickel catalyst with CEI on nickel foam (NiF@CEI‐Ni) shows the highest DBFC peak power density (0.59 W cm−2) with a non‐noble metal anode catalyst.

Low interfacial pH discloses the favorable biodegradability of several Mg alloys

Low interfacial pH (7.5–8.0) and corrosion rate were found for several Mg alloys (CP-Mg, UHP-Mg, Mg-0.15 wt%Ca, Mg-4 wt%Ag) in Ca2+-containing Hanks’ Balanced Salt Solution (HBSS, pHinitialbulk = 7.4) at 37 °C under hydrodynamic condition. Low interfacial pH and corrosion rate originated from the facilitated formation of the protective calcium-phosphate-rich precipitates at 37 °C. This study indicates that Mg degradation in a quasi-physiological environment causes only slight alkalization (pH < 8.0), as opposed to the high local and bulk pH (ca. 10.4) characteristic for Mg in NaCl electrolyte. It is also stressed that no synthetic pH buffers should be added to constantly supplied Ca2+-containing HBSS.

Nanoporous tin oxides for efficient electrochemical CO2 reduction to formate

CO2 electroreduction reaction (CO2RR) has been considered as an effective technology to close the anthropogenic carbon cycle. Formate, a product of two-electron transfer in CO2RR, is an economically valuable feedstock. In this work, nanoporous tin oxides were controllable synthesized by a facile and scalable electrochemical anodic oxidation method. XPS result indicated that the increased Sn4+ species after anodic oxidation were beneficial to reduce the overpotential of formate formation. Operando Raman spectra revealed that the enhanced formate selectivity could be attributed to the high local pH within the porous structure, which suppresses hydrogen evolution reaction (competing reaction against CO2RR). Further flow cell test showed a formate partial current density of 285 mA cm−2 with the selectivity of 96.4%, indicating a promising industrial application prospect.

The Influence of the Oxygen Reduction Reaction (ORR) on Pt Oxide Electrochemistry

AbstractIn this study, we employed microelectrodes and scanning electrochemical microscopy (SECM) to investigate the role of molecular oxygen and local pH changes on the electrochemistry of Pt oxide. We show that in acidic media and alkaline conditions, the impact of O2 is negligible, while in unbuffered neutral media, O2 strongly affects the formation of Pt oxides. Experiments carried under hindered diffusion reveal that this is due to a high local pH arising from the oxygen reduction reaction. This is evidenced by the appearance, at very positive potentials, of a diffusion controlled wave consistent with the oxidation of OH−. The ORR produces a sufficiently alkaline environment near the electrode to promote the formation of oxide at much more negative potentials than anticipated from the bulk pH. As a result, the onset of oxide formation overlaps the onset of oxygen reduction and it is impossible to obtain a Pt surface free from oxide at potentials positive of the onset of the ORR. Thus, prior exposure of the Pt surface to dissolved oxygen does not leave irreversibly adsorbed oxygen species as previously reported by our group; instead, the ORR induces a coverage of oxide at much lower potentials than determined by the bulk pH.

Simultaneous electrochemical degradation of organophosphorus pesticides and recovery of phosphorus: Synergistic effect of anodic oxidation and cathodic precipitation

To address future phosphorus scarcity and organophosphorus pesticides discharge associated environmental problems, a filter-press type electrochemical system was developed for acephate, a typical organophosphorus pesticide, degradation and simultaneous recovery of phosphorus. In this reaction system, boron-doped diamond (BDD) mediated anodic oxidation could transform acephate into ortho-phosphate (o-PO4) and then o-PO4 was precipitated with Ca2+ at the cathode surface in the form of hydroxyapatite induced by the local basic environment. The phosphorus recovery efficiency raised from 57 % to 92 % within 180 min by elevating current density from 5 to 30 mA/cm2, accompanying the enhanced acephate mineralization efficiency from 77% to 97%. These enhancement trends were attributed to the increased yield of BDD(•OH) and higher local pH near the cathode, respectively, at higher current density applied. Phosphorus recovery efficiency swelled by 15% with solution pH decreasing from 9.0 to 4.0 since anodic oxidation of acephate into o-PO4 was favorable in the acid solution. Moreover, phosphorus recovery was seriously depressed in the initial reaction stage with the presence of Mg2+, whereas bicarbonate posed the negative effect over the whole reaction process. Unexpectedly, the presence of Cl− inhibited the degradation of acephate since highly oxidative •OH was consumed by Cl−. In general, the electrochemical strategy of “anodic oxidation-cathodic precipitation” has been demonstrated practicable for phosphorus recovery from the organophosphorus wastewater.

Degradation study for the membrane electrode assembly of anion exchange membrane fuel cells at a single-cell level

The cathode side catalyst and binder were severely deteriorated compared to the membrane and that of the anode side during the constant current operation. This is due to the high local pH of the cathode caused by the water imbalance inside the MEA.

Graphene-modified graphite paper cathode for the efficient bioelectrochemical removal of chromium

Metal-free electrocatalysts have been widely used as cathodes for the reduction of hexavalent chromium [Cr(VI)] in microbial fuel cells (MFCs). The electrocatalytic activity of such system needs to be increased due to the low anodic potential provided by bacteria. In this study, graphite paper (GP) was treated by liquid nitrogen to form three-dimensional graphite foam (3DGF), improving the Cr(VI) reduction by 17% and the total Cr removal by 81% at 30 h in MFCs. X-ray absorption spectroscopy confirmed the Cr(VI) reduction product as Cr(OH)3. Through the spectroscopy characterizations, electrochemical measurements, and density functional theory calculations, the porous structures, edges, and O-doped defects on the 3DGF surface resulted in a higher electro-conducting rate and a lower mass transfer rate, which provide more active sites for the Cr(VI) reduction. Additionally, the scrolled graphene-like carbon nanosheets and porous structures on the 3DGF surface might limit the OH− diffusion and result in a high local pH, which accelerated the Cr(OH)3 formation. The results of this study are expected to provide a simple method to manipulate the carbon materials and insights into mechanisms of Cr(VI) reduction in MFCs by the 3DGF with in situ exfoliated edges and O-functionalized graphene.

Coordination-Cage-Catalysed Hydrolysis of Organophosphates: Cavity- or Surface-Based?

The hydrophobic central cavity of a water‐soluble M8L12 cubic coordination cage can accommodate a range of phospho‐diester and phospho‐triester guests such as the insecticide “dichlorvos” (2,2‐dichlorovinyl dimethyl phosphate) and the chemical warfare agent analogue di(isopropyl) chlorophosphate. The accumulation of hydroxide ions around the cationic cage surface due to ion‐pairing in solution generates a high local pH around the cage, resulting in catalysed hydrolysis of the phospho‐triester guests. A series of control experiments unexpectedly demonstrates that—in marked contrast to previous cases—it is not necessary for the phospho‐triester substrates to be bound inside the cavity for catalysed hydrolysis to occur. This suggests that catalysis can occur on the exterior surface of the cage as well as the interior surface, with the exterior‐binding catalysis pathway dominating here because of the small binding constants for these phospho‐triester substrates in the cage cavity. These observations suggest that cationic but hydrophobic surfaces could act as quite general catalysts in water by bringing substrates into contact with the surface (via the hydrophobic effect) where there is also a high local concentration of anions (due to ion pairing/electrostatic effects).

Polydopamine-on-liposomes: stable nanoformulations, uniform coatings and superior antifouling performance.

Polydopamine (PDA), a mussel-inspired synthetic polymer, affords biocompatible and antifouling coatings on a variety of surfaces. However, the traditional protocol of preparing PDA by polymerizing dopamine (DA) under basic conditions yields physically-unstable and non-uniform coatings that are prone to delamination and exhibit compromised antifouling performance in vivo. Here, we show that the high local pH in the vicinity of vesicular self-assemblies formed by a series of acetal-based cationic amphiphiles can be exploited to conveniently polymerise DA under physiological conditions in a gradual manner without requiring any external oxidant. Two of the four PDA-liposome nanoformulations viz. PDA-L1 and PDA-L2 turned out to be highly stable physically and resisted precipitation for more than a month while the other two formulations (PDA-L3 and PDA-L4) were less stable and formed visible precipitates with time. Further, the PDA-liposome formulations had significantly improved haemocompatibility compared to that of pristine liposomes. PDA-L1 formed highly uniform, nanostructured coatings on implants like catheter, cotton and bandages that did not delaminate even after a week of continuous incubation in simulated body fluid, or on exposure to pH change and presence of proteolytic enzymes. The PDA-L1 coated catheter implants resisted biofouling by both Gram-positive and Gram-negative bacteria in vitro and also had superior in vivo performance in mice vis-à-vis the implants coated with traditional base-polymerised PDA formulation (BP-PDA). Thus, these novel liposomal PDA nanoformulations significantly improve the practical utility of PDA-based coatings for antimicrobial applications.

Boosting Electrochemical Reduction of CO2 at a Low Overpotential by Amorphous Ag‐Bi‐S‐O Decorated Bi0 Nanocrystals

AbstractBimetal‐S‐O composites have been rarely researched in electrochemical reduction of CO2. Now, an amorphous Ag‐Bi‐S‐O decorated Bi0 catalyst derived from Ag0.95BiS0.75O3.1 nanorods by electrochemical pre‐treatment was used for catalyzing eCO2RR, which exhibited a formate FE of 94.3 % with a formate partial current density of 12.52 mA cm−2 at an overpotential of only 450 mV. This superior performance was attributed to the attached amorphous Ag‐Bi‐S‐O substance. S could be retained in the amorphous region after electrochemical pre‐treatment only in samples derived from metal‐S‐O composites, and it would greatly enhance the formate selectivity by accelerating the dissociation of H2O. The existence of Ag would increase the current density, resulting in a higher local pH, which made the role of S in activating H2O more significantly and suppressed H2 evolution more effectively, thus endowing the catalyst with a higher formate FE at low overpotentials.

Boosting Electrochemical Reduction of CO2 at a Low Overpotential by Amorphous Ag‐Bi‐S‐O Decorated Bi0 Nanocrystals

Bimetal-S-O composites have been rarely researched in electrochemical reduction of CO2 . Now, an amorphous Ag-Bi-S-O decorated Bi0 catalyst derived from Ag0.95 BiS0.75 O3.1 nanorods by electrochemical pre-treatment was used for catalyzing eCO2 RR, which exhibited a formate FE of 94.3 % with a formate partial current density of 12.52 mA cm-2 at an overpotential of only 450 mV. This superior performance was attributed to the attached amorphous Ag-Bi-S-O substance. S could be retained in the amorphous region after electrochemical pre-treatment only in samples derived from metal-S-O composites, and it would greatly enhance the formate selectivity by accelerating the dissociation of H2 O. The existence of Ag would increase the current density, resulting in a higher local pH, which made the role of S in activating H2 O more significantly and suppressed H2 evolution more effectively, thus endowing the catalyst with a higher formate FE at low overpotentials.

In-situ disintegration of egg white gels by pepsin and kinetics of nutrient release followed by time-lapse confocal microscopy

Digestion behaviour of food protein-based hydrogels is greatly influenced by the gel characteristics and in particular the microstructure. Using egg white gels (EWGs) as a model food, this study aimed to explore the real time disintegration by pepsin of different microstructures and subsequent nutrient release kinetics. Using thermal treatment at 80 °C, EWGs with two different microstructures but similar protein concentration (10%) were produced by varying the pH conditions (pH 5 and pH 9). The in situ spatiotemporal disintegration of the microstructure during static in vitro gastric digestion was followed using a high resolution confocal microscopic technique. Tetramethylrhodamine isothiocyanate (TRITC)-dextran (4400 Da) was incorporated into the gels as a model fluorescent molecule of peptide-like size, to trace its release due to the pepsin action. The looser microstructure of pH5-EWG caused the gel to disintegrate more quickly and to a greater extent, leading to a higher rate of TRITC-dextran release. In contrast, the compact-dense microstructure of the pH9-EWG showed slower kinetics of disintegration and (TRITC)-dextran release, likely due to a reduced accessibility of pepsin to its substrates. Pepsin activity being highly pH-dependent, high local pH and high buffering capacity of pH9-EWG may also play a pivotal role in the slower disintegration observed for this gel. In both EWGs, spatial degradation was mainly observed at the gel surface while the interior area fractions remained unchanged. Thus, surface erosion is possibly the underlying mechanism of EWG disintegration by pepsin in these experimental conditions.

In vitro and in vivo anti-corrosion properties and bio-compatibility of 5β-TCP/Mg-3Zn scaffold coated with dopamine-gelatin composite

Mg alloy is an excellent biomaterial due to its ideal mechanical properties, bio-degradability and bio-compatibility. However, high local pH, subcutaneous gas pockets and compromised mechanical integrity caused by high degradation rate restrict its clinical application. The purpose of this study is to improve the anti-corrosion properties of 5β-TCP/Mg-3Zn scaffold using poly-dopamine/gelatin (PDA/G) composite coatings through an easy, convenient and cheap dipping method. We found that dopamine (C8H11NO2) slowed down corrosion by forming thin, surface-adherent PDA films on the scaffold surface. Gelatin formed a dense organic membrane cover on the rough surface which results from the processing of PDA membrane to seal the macrocracks and protect it from corrosion. As compared to bare 5β-TCP/Mg-3Zn alloy, electrochemical tests showed that the corrosion current density (icorr) decreased from 5.24 × 10−3 A/cm2 to 1.41 × 10−3 A/cm2, indicating improved anti-corrosion properties. The soaking results indicated that pH values of immersion solution, as well as the volumes of released hydrogen, were 9.83 and 9.25, 20 mL and 15 mL for bare and coated alloy, respectively, indicating that the composite coating enhanced the anti-corrosion property of Mg alloy. The in vitro cytotoxicity test showed that 10%, 50% and 100% concentration of the immersion solution were safe for cellular applications. The in vivo test showed that serum magnesium concentration for PDA/G was lower than that of the bare sample. In addition, the materials and coatings were nontoxic to muscle and other vital organs, including heart, liver, kidney, and muscle. Moreover, the PDA/G composite coating showed a better anti-corrosion property in vivo than the bare sample and displayed a longer service time. These results suggest that coating of 5β-TCP/Mg-3Zn scaffold with PDA/G slowed down the corrosion rate of Mg alloy.

Cu-Based Bimetallic Electrocatalysts for CO2 Electrochemical Conversion to Valuable Chemicals: Study of Product Selective Distribution

The carbon dioxide emissions contribute largely to the global climate change, and this may lead to serious consequences, such as ice melting at the Earth’s poles and the fast-rising of the sea level [1]. The conversion of CO2 to molecules with higher energy is a possible strategy for fuel and/or chemical reactant production or even energy storage. In this context, different metal electrocatalysts are under investigation, but only copper seems to be effective for generating hydrocarbons, mainly methane (CH4) and ethylene (C2H4) [2]. However, further advances are still necessary to increase its product selectivity and stability. Considering this scenario, in this study, the selectivity and stability of copper-based electrocatalysts for the CO2 electrochemical reduction, in KHCO3 aqueous electrolyte, was investigated by on-line Differential Electrochemical Mass Spectrometry (DEMS), under different reaction conditions. Polycrystalline bulk copper electrodes (Cu rod of a rotating electrode) produced only CH4 as the reaction product in the first scan from -0.5 to -2.4 V vs. Ag/AgCl. However, in the subsequent scans, the signal for C2H4 became evident and its magnitude increased, while that for CH4 decreased. During long-term potentiostatic polarization at -2.0 V, after ca. 1 h, CH4 was suppressed and only C2H4 was observed, this being stable for more than 7 h. After this period of polarization, XRD analysis revealed the formation of copper hydroxide. When the reaction was conducted on copper oxide, only C2H4 was observed. Although the Cu2O phase suffer reduction to metallic copper, as revealed by EXAFS [3], some superficial (and metastable) hydroxides may remain or be sustained by the OH- species that are produced during the CO2 reduction in the aqueous media. The formation of OH- may also be responsible for the observed copper hydroxide phase on the surface of the bulk copper electrode, after 7 h of polarization. Interestingly, when the concentration of KHCO3 was reduced from 0.5 to 0.1 molL-1 (reduced buffer capacity) the DEMS signal for C2H4 was increased for all cases, as observed before [4]. These results point out to an important role of the superficial oxides/hydroxides (or high local pH) on the selectivity for C2H4. Importantly, in addition to the increase in the selectivity, it is noted an increase in the stability of the electrocatalyst when the reaction is totally deviated to the formation of C2H4 [5]. The necessary presence of hydroxides on the copper surface for the C2H4 formation is further confirmed when palladium was co-deposited or alloyed with copper. As palladium induces the hydrogen spillover, copper is already present in the metallic state in the as-prepared material, and remains in the same reduced state even after the CO2 reduction, as revealed by XRD analyses. This copper-palladium electrocatalyst produced only CH4 and H2 (to a higher extent), with no measurable C2H4 signal. The adsorbed hydroxide species (or high local pH) may favor the electron transfer with non-simultaneous proton transfer, which favor pathways of CO – CO coupling species, producing ethylene as the final product [4]. Acknowledgements The authors gratefully acknowledge financial support from FAPESP (2014/26699-3, 2016/13323-0 and 2013/16930-7), CAPES and CNPq (306469/20162). [1] H. Khatib, Energy Policy, 2012, 48, 737–743. [2] Hirunsit, P., Soodsawang, W., Limtrakul, J., J. Phys. Chemistry C, 2015, 119, 8238–8249. [3] Camilo, M. R., Silva, W. O., Lima, F. H. B. J. Braz. Chem. Soc., 2017, 28, 1803–1815. [4] Kas, R., Kortlever, R., Yılmaz, H., Koper, M. T. M., Mul, G., ChemElectroChem, 2015, 2, 354 – 358. [5] Dinh, C., Burdyny, T., Kibria, MD G., Seifitokaldani, A., Gabardo, C. M., de Arquer, F. P. G., Kiani, A., Edwards, J. P., de Luna, P., Bushuyev, O. S., Zou, C., Quintero-Bermudez, R., Pang, Y., Sinton, D., Sargent, E. H., Science, 2018, 360 (6390), 783–787.

Branched Copper Oxide Nanoparticles Induce Highly Selective Ethylene Production by Electrochemical Carbon Dioxide Reduction.

For long-term storage of renewable energy, the electrochemical carbon dioxide reduction reaction (CO2RR) offers a promising option for converting electricity to permanent forms of chemical energy. In this work, we present highly selective ethylene production dependent upon the catalyst morphology using copper oxide nanoparticles. The branched CuO nanoparticles were synthesized and then deposited on conductive carbon materials. After activation, the major copper species changed to Cu+, and the resulting electrocatalyst exhibited a high Faradaic efficiency (FE) of ethylene reaching over 70% and a hydrogen FE of 30% without any byproducts in a neutral aqueous solution. The catalyst also showed high durability (up to 12 h) with the ethylene FE over 65%. Compared to cubic morphology, the initial branched copper oxide structure formed highly active domains with interfaces and junctions in-between during activation, which caused large surface area with high local pH leading to high selectivity and activity for ethylene production.

Boosting CO Production in Electrocatalytic CO2 Reduction on Highly Porous Zn Catalysts

Earth-abundant electrocatalysts are desirable for the efficient and selective reduction of CO2 to value-added chemicals. Here, a low-cost porous Zn electrocatalyst is synthesized using a facile electrodeposition method to boost the performance of CO2 electrocatalytic reaction (CO2RR). In an H-cell reactor, the porous Zn catalyst can convert CO2 to CO at a remarkably high faradaic efficiency (FE, ∼95%) and current density (27 mA cm–2) at −0.95 V versus the reversible hydrogen electrode. Detailed electrokinetic studies demonstrate that instead of the enhanced intrinsic activity, the dramatically increased active sites play a decisive role in improving the catalytic activity. In addition, the high local pH induced by the highly porous structure of Zn results in enhanced CO selectivity because of the suppressed H2 evolution. Furthermore, we present a straightforward strategy to transform the porous Zn electrode into a gas diffusion electrode. This way, the CO2RR current density can be boosted to 200 mA cm–2 w...

Comparing the electrocatalytic reduction of CO2 to CO on gold cathodes in batch and continuous flow electrochemical cells

The electrocatalytic reduction of CO2 on gold cathodes was found to differ significantly between a standard batch electrochemical cell and a flow cell incorporating a porous gold cathode. While the well-known influence of KHCO3 concentration on product selectivity was observed in the batch cell, the selectivity of the CO2 reduction reaction was shown to be independent of KHCO3 concentration in the flow cell. The Faradaic efficiency for CO production was found to be 80–90% regardless of the KHCO3 concentration whereas in the batch cell it decreased from 75% to 35% as the KHCO3 concentration is increased from 0.05 to 0.5 mol L−1. The current density was found to be independent of the KHCO3 concentration and similar in both cells (−4 to −10 mA cm−2 at −1.3 V vs Ag|AgCl). As the KHCO3 concentration effect is normally attributed to changes in the local pH at the cathode–electrolyte interface brought about by the buffering action of the electrolyte, the results found in this work suggest that pH buffering can be suppressed or manipulated in some cell/electrode configurations. In the flow cell used in this work, it is suggested that poor transport of the KHCO3 through the porous cathode support to the active surface results in higher local pH than that found at the surface of a cathode immersed in a traditional batch cell.

Importance of Proton Concentration on the Product Selectivity of the CO2 Reduction Reaction

The electrochemical CO2 reduction reaction (CO2RR) is seen as promising route for converting waste CO2 and excess renewable energy into valuable chemicals and synthetic fuels. During this process a variety of carbon-based products such as CO, HCOOH and hydrocarbons can be formed. The cathode material plays a crucial role on determining the product distribution during the CO2RR. For example, Cu has been found to be an interesting material on which CO2 is directly reduced to alcohols and hydrocarbons. (1) While, Ag based catalyst (2) and metal nitrogen doped materials (MNCs) are considered promising catalyst for the reduction of CO2 to CO.(3) In addition to the catalysts material, the pH and local pH are known to be key on determining the selectivity of the reaction. In the case of Cu catalysts, we have shown that the ratio between methane and ethylene prodiuction is strongly dependent on the local pH as ethylene formation is not affected by the proton concentration. As result, in conditions in which a high local pH is favored ethylene is the predominant product, while at low pH values CH4 is favored. (4) In the case of carbon base materials, however, the influence of the reaction conditions on the catalytic performance has not been addressed. Herein we looked into the role of the electrolyte on the selectivity of FeNC materials on CO2RR selectivity. (5) Unlike hydrogen or methane generation, CO production is independent on proton concentration on the NHE scale, suggesting a decoupled proton-electron transfer mechanism for CO formation. The similarity of the reaction mechanism with that of Metal-N macrocyclic complexes is an indication that the Fe centers incorporated to our carbon material indeed behave as the active centers of complex based catalysts. Furthermore, our results show that on doped carbon catalysts, such as FeNC, the selectivity towards the CO2RR can be conveniently tuned by the proton availability in both aqueous and non-aqueous electrolytes.