Sustainable membrane-coated electrodes for CO2 electroreduction to methanol in alkaline media

CO2 electroreduction has high potential to combine Carbon Capture Utilization and energy storage from renewable sources. The key challenge is the construction of highly efficient electrodes giving optimal CO2 conversion to high-value products. In this regard, research on electrode structures remains as an important task to face. Despite the advancements in gas diffusion electrodes (GDEs) to facilitate CO2 transfer and electrode efficiency, catalyst is still vulnerable to be swept by the gas and the liquid electrolyte, reducing the stability. We report the fabrication of novel membrane coated electrodes (MCEs), by coating an anion exchange membrane over a copper (Cu):chitosan (CS) catalyst layer onto the carbon paper. CS and poly(vinyl) alcohol (PVA) were chosen for membrane preparation and catalyst binder, where Cu was embedded in the polymer matrix as nanoparticles or ion-exchanged in a layered stannosilicate or zeolite Y, to improve their hydrophilic, conductive, mechanical and environmentally-friendly properties considered relevant to the sustainability of the electrode fabrication and performance. The intimate connection between the CS:PVA polymer membrane over-layer and the CS/Cu catalytic layer


INTRODUCTION
Over the past few years, we have observed how the impacts of climate change throughout the planet are increasing dramatically, and so is the global urgency to take measures against them.
As a matter of fact, two different observatories have recently recorded the alarming concentration of carbon dioxide in the atmosphere of 415 ppm [1,2] . Therefore, different techniques for the Carbon Capture, Utilization and Storage (CCUS) are being studied to reduce CO2 emissions and to use it as raw material in industry, in response to the Circular Economy [3] . The combination of CCUS with a renewable energy production model makes the electrochemical reduction of CO2 (CO2RR) a plausible technological alternative, by simultaneously confronting the energy storage from renewable sources and the CO2 transformation into value added products [4] .
However, the electrochemical conversion of CO2 is still a challenging subject. One of the main issues is the fabrication of electrodes that provide productive and efficient transformation of CO2 at low overpotentials. To this effect, it is important to improve the effectiveness and selectivity of complex electrocatalysts [5] . Electrocatalysis is an interfacial phenomenon, where the relative ratio of CO2 and H2 (H + ) is dictated by the intrinsic selectivity of surface active sites and the local concentration of reaction compounds involved in the different rate-controlling stages. Therefore, there is an urgent need for understanding the mechanisms involved in order to design more effective electrodes [6,7] . In this regard, many researchers focus on the catalyst composition, being copper one of the most studied metals [8][9][10][11] . Besides composition, surface structure and morphology also plays a relevant role in electrode performance. The effect of surface morphology on the CO2RR to alcohols or hydrocarbons has been studied in the form of Cu-coated nanospikes [12] , nanowires [13] or Metal Organic Frameworks (MOFs) [14,15] , among others. The micro and meso structure of the electrode determines the diffusional gradients under steady-state conditions. Steady-state conditions are the most commonly investigated in CO2/HCO3electrolytes because their slow equilibration kinetics leads to the mass transfer limited region. In order to facilitate CO2 transfer to the catalyst and improve the performance of the electroreduction process, researchers have applied high pressure [16] , gas diffusion electrodes (GDEs) [17,18] , taking advantage of the higher surface of catalyst accessible to the CO2, and metal coated ion-exchange membrane electrodes (CCMs) [19] . However, material losses and degradation hinder the durability of the electrodes in continuous flow electrochemical cells for CO2 reduction [7,19,20] .
Apart from the electrodes and catalysts, another important device that may play a significant role in the electrolytic cell are the ion exchange membrane (IEM) [21,22] and the electrochemical environment [5] . The most studied configuration in flow reactors are membrane reactors, where the membrane role consists just on the physical barrier that separates the anode and the cathode and facilitates the selective transport of ions between them to close the circuit, while simultaneously attenuating the cross-over in the opposite direction and the re-oxidation of the product. [23] In order to avoid the challenges of using liquid electrolytes, to improve CO2 solubility and recovery of liquid products, solid polymer electrolyte membranes were introduced in the design of electrochemical flow reactors [7,19,20] . The development of alkaline anion-exchange membranes (AAEMs), bipolar membranes and mosaic membranes in opposition to most conventionally employed cation exchange membranes (CEMs), Nafion 117 (DuPont) [24][25][26] , is an example of the increasing relevance that the role of the IEM in the electrochemical reaction is gaining in research literature [10] . Despite the predominance of CEMs, the most widely studied electrochemical environment for CO2RR is slightly alkaline (almost neutral) rather than acid medium, in order to reduce the influence of the Hydrogen Evolution Reaction (HER) that otherwise competes with CO2RR. Thus, AAEMs are attiring the attention as to their suitability for this process [4,27] . Also, high alkaline pH has been observed to influence CO2 reduction on Cu catalyst surfaces, due to the hydroxide ions role in modulating the catalyst surface and suppressing the HER [19] . AAEMs work by facilitating the flow of anions (e.g. OH -) from the cathode to the anode. In CO2 electrolyzers working in alkaline conditions, OHions rapidly react in the presence of CO2 to form HCO3and CO3 2but the lower mobility of the latter ions compared to OHusually inhibit ion transport and reduce CO2 reduction efficiency [19] . Thus the anion transport mechanism is expected to be more limiting for CO2RR with systems using AAEMs than CEMs because the forward reaction of CO2 to products is encouraged without delivering H + to the cathode. And yet, some of the best performing CO2 flow cells known today use AAEMs [28,29] . Through commercial anionic membranes as FAA-3 (Fumatech) [30] or A-901 (Tokuyama) [31] , the rate of product crossover was proportional to the current density. Aeshala et al. highlighted the improved CO2RR efficiency of quaternary ammonium groups in anionic solid polymer electrolytes. [32] Dioxide Materials developed Sustainion@, an AAEM containing imidazolium compounds that improve the performance and selectivity of CO2RR to CO [28,29,33] . However, these membrane materials and preparation are usually expensive or highly toxic to health and environment. Thereby, the search for renewable and more economic polymers in membrane preparation is a key factor to ensure the future sustainability of the process [34] . There, chitosan (CS) is a great alternative in this regard and its use in electrochemical devices has been reviewed [35] , leading to intensive work, especially in the framework of alkaline fuel cells [36] . The conductivity and the mechanical stability of CS can be tuned up by blending with low-cost poly(vinyl alcohol) (PVA), and different metal or ionexchange porous structured fillers embedded in the polymer matrix, for further functionalizing the membrane properties for electrochemical applications, by the Mixed Matrix Membranes (MMM) approach [37] .
Then, the concept of membrane coated electrocatalysts (MCEC) came across recent literature, as an alternative to improve the stability of electrocatalysts for electrochemical devices, from sensors to fuel cells, as a mean of controlling the interfacial phenomenon of electrocatalysis and the local concentration of reaction compounds and catalyst sites involved in the different ratecontrolling stages [38] . Likewise, the encapsulation of metal electrocatalysts in different matrices has been reported to have a significant influence on the CO2RR selectivity and stability, depending on the nature of the polymer. Protective membrane layers composed of metal oxides [39,40] have been proposed for HER and Methanol Oxidation Reaction, and conductive polymers [41][42][43][44][45] have been studied for the CO2 electroreduction at chemistry laboratories, where the polymer both protects the catalytic layer and boosts the ion transport to the active sites, thus reducing the required over potentials [42,46] and slightly improving the efficiency of the CO2 electrochemical reduction in different media. This creates a new field for research that we may call "membrane coated electrodes (MCEs)". As an example, polypyrrole (Ppy) coating has been recently observed to increase the stability, conductivity, and catalytic activity of Cu2O shape structures on paper electrodes in CO2RR in aqueous electrolyte medium [47] . With these new MCE structures, new reaction pathways and mechanisms may be possible, and the product selectivity can be tuned up by applying a transport-mediated reaction selectivity and the protective layers controlling the mass and ion transport to the metal electrocatalyst, by anticipating that rapid transport to the electrode and through a thin membrane and analyte pre-concentration in the membrane improve the sensitivity of the system [38] . Likewise, we believe that the dispersion of metal particles into a conductive polymeric matrix may provide synergies with the specific areas of metal catalyst and thus improve the catalytic efficiency [37] . For instance, the hydrophilicity and crossover, a major challenge in fuel cells, has been controlled by coating a silica sol-gel derived over-layer to Nafion membranes [40] .
The improvement on anion conductivity, mechanical resistance and hydrophilic character is desirable for an overall better behavior of the MCE. In this work, GDEs for the electroreduction of CO2 have been prepared using Cu nanoparticles (NPs) and CS biopolymer solution as binder of the catalytic layer sprayed on carbon paper, instead of Nafion (DuPont) or Fumion (Fumatech).
The MCE was prepared by coating a membrane over-layer on top of the new GDE. This membrane over-layer was composed of a CS:PVA equimolar blend filled by different Cu-containing inorganic fillers, whose effect on the physico chemical and mechanical properties, among other features, was correlated with the membrane composition in a previous work [48] . The aim of the present work is evaluating whether the controlled anion conductivity, mechanical resistance and hydrophilic character of this membrane layer provides catalytic to the MCE in the CO2RR to other products, and simultaneously provides surface electrode protection in terms of electrode efficiency and stability in an undivided electrochemical cell. As such, the alkaline anion exchange membranes (AAEMs) composed of Cu/CS:PVA, Cu-UZAR-S3/CS:PVA and Cu-Y/CS:PVA mixed matrix membranes (MMMs) were selected as membrane over-layer in this work on account of the permeability, hydrophilicity and conductive and mechanical resistance, respectively. A pure CS:PVA polymer membrane over-layer was also characterized in this work, as well as an uncoated GDE without membrane over-layer were also evaluated for comparison purposes.

Preparation of CS:PVA polymer coated electrodes
The prepared MCEs were composed of three layers, as schematized in the configuration plotted in Figure 1, consisting of a bottom porous carbon paper (Toray TGP-H-60) acting as conductive macroporous support and gas diffusion layer (GDL), a catalytic layer where the catalytic ink is composed of Cu NPs (60-80 nm Sigma Aldrich, Spain) and CS aqueous solution, prepared from a 1 wt. % solution of CS (coarse ground flakes and powder, 310,000 -375,000 Da and 75% deacetylation degree, Sigma Aldrich) as binder, and a membrane over-layer over the GDE. The catalyst:binder mass ratio was 70:30 in all cases. Water was added to the binder as vehicle and the final concentration of solids (Cu + CS) was 3 wt. %. The ink was sonicated for 20 min and air-brushed onto the carbon paper. For the membrane over-layer fabrication, an equimolar blend of CS and PVA (powder, 85,000 -120,000 Da and 99+% hydrolyzed, Sigma Aldrich) were stirred for 24h, from previously prepared aqueous solutions of CS 1 wt. % and PVA 4 wt. %, respectively. [48] The polymer solution was cast over the GDE (carbon paper + catalytic layer) and left drying overnight at room temperature. When the solvent was evaporated, the solid membrane layer was perfectly fixed and integrated as part of the electrode. Electrodes were then immersed in NaOH 1M for the activation of the alkaline anion exchange membrane (AAEM) over-layer. The geometric surface area of the electrodes was 10 cm 2 and its catalytic loading, 1 mg/cm 2 .

Preparation of mixed matrix membrane coated electrodes
The same procedure was followed for the preparation of the mixed matrix MCEs, by adding different Cu-based fillers to the polymeric CS:PVA blend prior to the casting over the catalytic layer. Three fillers were selected from our previous work, on account of their water uptake and water vapor permeability, ion exchange capacity and conductivity, and tensile strength, respectively: commercial Cu NPs, Cu-exchanged on layered stannosilicate UZAR-S3 (Cu-UZAR-S3) or zeolite Y (Cu-Y). [48] It was expected that the implications observed on the stability of the Cu oxidation state in Cu NPs, Cu-exchanged in layered silicates and Cu-exchanged in zeolites may lead to a different catalytic activity of the MCE, and not only due the Cu additional content. Cu-UZAR-S3 and Cu-Y selected loadings were 10 wt. % of the total solid content of the membrane, as the optimal from the previous work, [48] while for Cu NPs, the filler loading was kept below 5 wt.% because the addition of higher Cu NPs loadings decreased the solution viscosity so much that the membrane casting upon MCE preparation was very cumbersome. Table 1 enumerates the different electrodes prepared as a function of membrane over-layer composition.

Electrochemical experiments
The electrochemical behavior was first studied by performing cyclic voltammetry (CV) on the as-prepared electrodes in Table 1 with CO2 before the experiments and continuously aerated during the electro reduction process.
Potentials over Ag/AgCl were set at -0.3V, -0.5V, -1.0V and -1.5V, after the CV observations. The duration of each experiment was 60 min. To determine product composition and concentration, liquid samples were taken and analyzed via gas chromatography-mass spectrometry (GC-MS-QP2010 Ultra, Shimadzu). The efficiency of the electron transfer towards the reduction of CO2 to products was determined by calculating the Faraday Efficiency (FE) to main products detected for every experiment, using Equation (1).
where z is the number of electrons exchanged, n is the moles of product generated, F is the Faraday constant (96484.5 C/mol) and q is the total charge applied, in Coulombs. and after aeration with N2, while this value descended to 10.5 after saturation with CO2 due to partial carbonation of KOH, which was constant along the voltammetry electrolysis experiment as was the pH. The potential was referred to the Reversible Hydrogen Electrode (RHE) as Evs RHE = Evs Ag/AgCl + 0.197 + 0.059 · pHelectrolyte, where pHelectrolyte was the initial pH of the solution [49] , in order to compare with literature.

Electrochemical characterization
In Figure 2, the reduction activity observed in the red voltammograms (no CO2) can be only be attributed to the electrode or H2O reduction (HER) contributions. Aydin et al. reported that at -0.7V vs Ag/AgCl, Cu wire presented a reduction peak [42] as the one appreciated for the Cu plate ( Figure 2a) and the uncoated GDE ( Figure 2b) in this work at lower overpotentials. A large oxidation activity was appreciated in the reverse scan, most remarkable in the Cu plate, which implies that the continuous metal plate electrode was extremely vulnerable to redox reactions during CV [49] . This oxidation activity was also observed, though less pronounced, in the uncoated CS:PVA/Cu GDE. This may be attributed to the structural differences between the Cu continuous plate and the Cu:CS GDE, although it has been hypothesized that the binding of an ionic polymer, i.e. CS, with the metal ion may slightly protect the Cu NP catalyst in the catalytic layer ( Figure   1) [50] from degradation, which does not occur in the Cu plate. This protection may also slightly reduce the number of active sites available for the reaction, while enhancing the activity of those that are indeed available, compared with the metal plate. In this sense, the MCEs seemed passivated since their voltammograms in Figures 2c-2f do not show those electrode contributions, so it can be expected that the membrane over-layer successfully reduced the degradation of the catalytic layer. [43] For all the electrodes tested, notorious current reductions were observed at overpotentials higher than -0.5V vs RHE, where HER is the predominant reaction. [17,51] In the CO2 saturated electrolyte, a reduction peak appeared at 0.25V vs RHE, attributed to CO2RR. This reduction activity was more significant for the MCEs with Cu-UZAR-S3/CS:PVA and Cu-Y/CS:PVA MMMs as membrane over-layers, whose voltammograms are represented in Figures 2e and 2f, respectively. Therefore, it could be advanced that the enhanced hydrophilicity, ion exchange capacity and anion conductivity of these membranes observed in our previous work, [48] may be leading to an improvement of the electrode behavior in CO2 electrochemical reduction.

Electrochemical reduction of CO2
Electroreduction experiments at constant potentials of -0.3V, -0.5V, -1.0V and -1.5V vs Ag/AgCl were carried out for 1h. These potential values were selected in agreement with the different stages observed in the CVs in Figure 2: at -0.3V, a first reduction process was observed, at -0.5V, we identified the CO2RR reduction process, at -1.0V, another reduction began, generating a high current density and, finally, at -1.5V, a great reduction current was involved, primary attributed to HER.
The current density generated at these potentials was stable over the full length of the experiments, as represented in Figure 3a, so steady state conditions were confirmed. Faraday for methanol at -1.0V at the times when the samples were taken. Table 2 presents the main results obtained in the CO2 electroreduction experiments at -1.0V and -1.5V vs Ag/AgCl (-0.18V and -0.68V vs RHE, respectively) for the electrodes prepared in this work. Both the uncoated Cu/CS GDE and the MCEs led to methanol as main product, which is attributed to the alkaline environment, [5] as well as water swelling [11,48] and surface morphology. [12] Some Cu-based GDEs from literature also directed to methanol as main product are also reviewed in Table 2 in order to verify that the current densities generated with our working electrodes were of the same order of magnitude as those reported by other researchers in undivided cells at low overpotentials. [52] For all the electrodes tested in this work, the current densities increased with increasing potential, although the lower potentials (-0.5V and -0.3V vs Ag/AgCl) are not included in Table 2 because the current densities generated in those conditions were too low to make the calculations reliable. The decreasing FE to methanol with increasing potential and current density at higher over-potentials can be allocated to the HER as the dominating reaction [17,51] . The uncoated GDE prepared in this work generated higher current densities and increased over-layers observed previously. [48]   largest water transport reported elsewhere [48] . Therefore, this Cu/CS:PVA membrane layer generated the highest current densities generated of all MCE in Table 2, but the catalyst in metallic form seemed to be less accessible for CO2 and its ionic forms, so the methanol production dropped, in favor of HER as dominant reaction. [56] As Cu in other polymer-coated electrodes studied in the state of Cu(II) [48] , their efficiency towards CO2 conversion was enhanced by the polymer coating. Aydin et al. observed that coating Cu-derived NPs with conductive polypyrrole over a Nafion 117 membrane, controlled the HER, compared to blank Cu as electrocatalyst, with a FE of 25% and 20% towards CH4 and formate, respectively, thus shifting the product selectivity and catalyst activity. [42] Grace et al. observed an improvement in the FE of CO2 to acetic and formic acids by coating Cu2O NPs electrodes with a polyaniline film, [57] even at low overpotentials. Ahn et al. reported that the coating of Cu foam electrode surfaces could both activate and stabilize the electrode surface towards different reaction intermediates. [58] Conductive polypyrrole could also increase the stability of Cu2O NPs in the CO2RR to methanol [47] .
The diffusion layer thickness can be estimated using the Nernst diffusion layer Equation where Iss is the steady state current, D is the diffusion coefficient of CO2 (1.9 x 10 -5 cm 2 /s at room temperature [59] ), C is the dissolved CO2 (aq) concentration in a fully saturated solution, 0.034 M [60] ), A, the geometric area of the working electrode and δ (cm) the diffusion layer thickness. The value obtained for the uncoated Cu:CS GDE in this work was of the same order of magnitude obtained in literature with other GDEs, so Equation (3), modified for a planar electrode by Billy and Co, [59] could be applied to calculate the diffusion layer thickness of our MCE, as where v is the estimated average CO2 flow rate, which in this work is 1 mL/min, and b as the membrane over-layer thickness in Table 1 respectively. These values are higher than those reported in literature, [58,59] though, confirming the additional resistance opposed by the membrane over-layer and expecting the existence of nonidealities when this membrane over-layer is a mixed matrix membrane (MMM), [61,62]  Because the CS:PVA MCE showed a better performance than the uncoated GDE prepared in this work, this was first attributed to the protection provided by the membrane over-layer and the CS binding properties in the catalytic layer mentioned earlier. [58] The encapsulation of a nanoparticulate metal catalyst in a membrane over-layer with OHfunctional groups that interact with the catalyst active sites and CO2-derived reagents can avoid the dissolution of metal NPs and facilitate the membrane fabrication in a mixed matrix containing ions. [38] The membrane overlayer of the Cu/CS:PVA MCE (Figure 4c) was thinner than that of the CS:PVA MCE (Figure 4b) after the electrolysis experiments. When the CS:PVA matrix of the membrane over-layer contained Cu exchanged in inorganic zeo-type fillers, although the oxidation state, hydrophilic, transport and mechanical properties were more promising than the pure CS:PVA polymer membrane material, as analyzed elsewhere, [48] Figure 4d reveals that this layer has collapsed into the carbonaceous porous support below, probably due to local decreases of pH in the electrode surface along the experimental run. The CS tends to dissolve in weak acid solutions and the longer stability of the Cu ion active for CO2RR when exchanged in zeolites and layered silicates as compared to the free metal NPs observed in our previous work may be lowering the local pH of the MCE surface. [63] Nevertheless, the EDX analysis revealed that both the Cu catalyst from the membrane over-layer and the NPs from the intermediate catalyst layer were present in the pores of the Toray paper, attaining a remarkable FE to methanol of 68.05% in the case of the Cu-Y/CS:PVA MCE at an over-potential of -0.18V vs RHE, as was already shown in Table 2. The design and tuning of the MCEs using renewable or low-cost polymer materials for the membrane over-layer and the binder of the catalytic layer can therefore be an attractive strategy toward enhancing the CO2RR performance in membrane-like reactors needed for large-scale implementation. [64] Commentaries on the hypothesized CO2 reduction mechanism The half-reactions we believe that are taking place in the anode and cathode, from analyzing the scarce, but growing, literature on CO2 reduction in alkaline media, will be presented here in an attempt to start explaining the experimental results described above. The electrolyte in this work was KOH 1M or 2M (no differences in CV performance were observed in the laboratory upon increasing the electrolyte concentration, so we focused to 1M), and taking into account that the solubility of CO2 in water 0.036M at STP conditions, The dissolution of CO2 in the electrolyte causes an acidification of the media, by Equations (5)- (7), as Keeping in mind that the GDE and MCEs studied in this work were activated in NaOH 1M prior to the CO2RR experiments, some of the bicarbonate ions generated are expected to be experiencing an ion exchange process as observed in literature [47] , These were the reactions taking place before the CO2RR experiments. During the electroreduction process, not only CO2RR occured, but also HER, which competed with the desired former reaction. For nearly neutral pH conditions usually reported in literature (Table 2), the typical half-reactions at the cathode for the production of methanol were proposed as follows [47,65,66] However, at high pH values in alkaline electrochemical cells as those used in this work, the reaction mechanism that may be taking place at the cathode is that of hydrogen produced from water electrolysis, [67] (for water electrolysis that was competing with CO2 electrolysis) Still the information reported in literature about the methanol production mechanism in highly alkaline media is scarce. CO was reported to be an intermediate from CO2 in most of the possible products, including methanol, and the reaction generally proposed was [4,23] When Cu was used as catalyst in the cathode at pH > 8 in the electrolyte solution, as The latter species produced in Equations (13)- (14) are unstable and may end up forming CH3OH [68] . In the production of methanol, 6 electrons are involved in the reaction. Thus, assuming that CO2RR in alkaline media generates bicarbonate anions as Equation (12) suggested, the halfreaction at the cathode would result in to HCOOH, CO, CH4 and CH3OH on a Cu catalyst. [8] For CH3OH, CO was generated as intermediate after a two pairs of − + + transferred to the adsorbed CO2, liberating a water molecule. Then, an aldehyde was generated after another pair − + + transferred. The final pair of − + + promoted methanol formation in water-swollen systems. [11] Periasamy et al. proposed a similar route for MeOH production [47] , by Assuming the participation of the same intermediates in the CO2RR to methanol in a high alkaline media as that employed in this work, the former equations can be replaced by Leading to the overall half-reaction, At the anode, the OER takes place, and the half-reaction in high alkaline media would be Therefore, the OH-generated according to Equation (20) It was expected that these renewable or economic polymers were adequate for membrane coating preparation, and the membrane over-layer kept the conditions of humidity and conductivity along the experiment, thus providing protection and higher stability to the catalyst and electrode. When the membrane over-layer was functionalized by the inclusion of ionexchangeable inorganic fillers, the physicochemical properties and electrode activity were improved, but the membrane over-layer was partially dissolved upon reaction and entered the pores of the carbonaceous substrate beneath. Further work should be directed to the understanding of the role of the membrane over-layer from the MMM non-idealities, [62] which agreed with those observed in the electrochemical reduction of CO2 to CH3OH, as well as investigating the performance in a continuous flow filter press cell reactor where the closed environment is expected to prevent the local effects affecting the overall performance, as well as allowing us to complete the mass balance by measuring the gas phase. This way, current system limitations, i.e. no division between the electrodes, which could cause re-oxidation of methanol at the anode or the low solubility of CO2 in aqueous solutions, could be overcome.

AUTHOR CONTRIBUTIONS
The manuscript was written through contributions of all authors.

ACKNOWLEDGMENTS
Financial support from the Spanish Ministry of Science and Universities under project grant CTQ2016-76231-C2-1-R is gratefully acknowledged. A.M.M. also acknowledges the FPI grant no. BES-2017-080795. Prof. Manuel Arruebo (Instituto de Nanociencia de Aragón, Universidad de Zaragoza) is also gratefully acknowledged for providing the SEM-EDX measurements. Anonymous reviewers are also deeply thanked for their insightful comments.

Table of Contents
Membrane-coated electrodes have been prepared by coating the electrode with a mixed matrix layer of chitosan and polyvinyl alcohol with non-toxic inorganic fillers; their performance in CO2 electroreduction to methanol in alkaline media has been evaluated.