For battery architectures that need a solid ion conductor with good contacting performance and high stability against electrochemical oxidation, polymerized ionic liquids (PIL) pose a valuable class of materials. The low conductivity of the binary PIL/ lithium salt system can be increased using a ternary ionic liquid acting as plasticiser. The conductive mechanism of the ternary system is however not fully understood. This work shows the shift in conduction mechanism for the ternary Li−/[1,3]PYR-/PDADMA-FSI system by increasing the lithium salt concentration and comparing the transfer mechanism to binary ionic liquid (IL) electrolyte analogues using pulsed field gradient (PFG) nuclear magnetic resonance (NMR), NMR relaxometry, Raman spectroscopy and electrochemical techniques. Two conducting regimes were found which show a strong trade-off between conductivity and transference number. In the low lithium salt regime (≤35 wt% LiFSI), cluster diffusion of aggregated lithium is the dominating mechanism leading to low transference numbers (0.04–0.15 at room temperature (RT)). The high salt regime (≥50 wt% LiFSI) shows diffusion through free lithium ion hopping transfer, which has a stronger dependence on temperature and yields higher transference numbers (0.31 at RT). Increasing lithium salt concentration shows an inverse linear correlation with conductivity. The electrochemical characteristics of ternary IL/PIL/lithium salt are shown to be highly tuneable by varying the lithium salt fraction, while it maintains excellent characteristics like processability, stability and mechanical function.

In Fig. 4(e) on page 6733 of this article, the legends in the graph for faradaic efficiency of CO and C2+ were misplaced. The original figure should be replaced with an updated one. Note that this correction does not have any impact on the main idea and conclusion of this article. The updated Fig. 4 is as follows. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers. (Figure presented).

Electrochemical carbon dioxide reduction (CO2R) is an attractive route to use renewable electricity to convert CO2 emissions to carbon-based chemicals. Continuous-flow electrolyzers with gas diffusion electrodes (GDEs) allow for the CO2R at high reaction rates. In addition to the electrolyzer configuration and operating conditions, the product selectivity strongly depends on the morphology of the electrocatalyst. This study demonstrates electrodeposition of copper (Cu) catalysts as a simple and efficient approach for preparing GDEs with good control over morphology. We study the influence of the activation process of the gas diffusion layer and the electrodeposition conditions on the morphology. Four Cu GDEs with different morphologies showed distinctly different current responses and product distributions. The partial current density for ethanol (jethanol) ranged from −18 mA cm–2 to −29 mA cm–2. Depending on the Cu GDE morphology, jethylene ranged between −25 mA cm–2 and −44 mA cm–2. Although the catalyst layers revealed surface restructuring after CO2 electrolysis, the morphologies remained distinctly different and retained the crystal structure of polycrystalline Cu. Electrodeposited Cu-GDEs maintained their selectivity for 6 h at a cell voltage of 4 V, representing a 5-fold improvement compared to sputtered Cu GDEs. Overall, this study demonstrates a facile approach for preparing GDEs with control over the catalyst morphology to tune CO2R to specific gaseous and liquid products.

Electrochemical CO2 reduction presents an opportunity to transform waste flue gas with water and renewable electricity into chemicals or fuels. However, the energy-intensive nature of purification of flue gas underscores the appeal of directly utilizing the flue gas streams containing impurities. In this study, we investigate the impact of SO2 impurities on CO2 electroreduction in two electrochemical cell geometries: an H-cell and a membrane electrode assembly (MEA) cell. We observe distinctly different behavior of the Ag on carbon black (Ag/CB) catalyst under SO2 impurities in the H-cell compared to the MEA cell, where SO2 impurities exhibit a more pronounced effect on Ag/CB catalysts in the H-cell than in the MEA cell. This difference is attributed to the higher solubility of SO2 in the electrolyte compared to CO2, resulting in an accumulation effect and causing differences in the SO2 concentration near the electrode between the H-cell and the MEA system. By depositing a very thin SiO2 coating on the outermost surface of the Ag/CB catalyst using atomic layer deposition (ALD), the impact of SO2 on the catalyst's selectivity is diminished. This is attributed to the permeability difference between CO2 and SO2 through the SiO2 coatings and results in a local SO2 concentration difference between samples with and without SiO2 coatings.

Carbon-supported nickel and nitrogen co-doped (Ni-N-C) catalysts have been extensively studied as selective and active catalysts for CO2 electroreduction to CO. Most studies have focused on adjusting the coordination structure of Ni-Nx active sites, while the impact of the carbon supports has often been overlooked. In this study, a series of Ni-N-C catalysts on different carbon supports, including carbon black (CB), multi-walled carbon nanotubes (CNT), and activated nitrogen-doped biochar (ANBC), were synthesized using a ligand-mediated method. The effect of the carbon support on the electrocatalytic performance for CO2 reduction was investigated at both low current densities, in a H-cell, and high current densities, in a MEA electrolyzer. All of the prepared Ni-N-C catalysts show good faradaic efficiencies (FE) toward CO production (up to ∼90 %), however, the onset potentials and partial current densities for CO production vary greatly. The textural properties of the carbon support and the distribution of Ni-Nx active sites on the carbon support are demonstrated as the main factors behind the performance differences. In particular, hierarchical porous structures with a large specific surface area are helpful to facilitate mass transport and improve the dispersion of active sites, which allows for a better CO2 reduction performance of Ni-N-ANBC compared to Ni-N-CB and Ni-N-CNT. This study demonstrates the importance of the carbon support for Ni-N-C catalysts and provides new insights into the design of efficient Ni-N-C catalysts for the CO2RR.

Recent progress in the electrochemical reduction of CO₂ (CO₂RR) has led to notable breakthroughs in generating C₂ compounds such as ethylene and ethanol. Nevertheless, the direct formation of C₃ products encounters significant limitations due to the C₂–C₁ coupling reaction, posing a considerable challenge to improving their faradaic efficiency. Here, a design for an elevated pressure cascade catalytic reactor to convert CO₂ to C₃ products in a two-step electrochemical process is presented. At 25 bar pressure, by regulating the potential of the cascade system and the electrolyte flow rate, a 40% selectivity for 2-propanol on a copper electrode placed upstream of a silver electrode that converts CO₂ to CO is reported. In cascade mode (with both silver and copper electrodes active), the C₃:C₂ oxygenate ratio significantly increases to 7 compared to the noncascade mode (copper only) with a modest ratio of about 0.6. Therefore, our elevated pressure cascade electrolysis approach demonstrates a notable step forward in CO₂ electroreduction to oxygenated C₃ products.

Despite the huge efforts devoted to the development of the electrochemical reduction of CO2 (ECO2R) in the past decade, still many challenges are present, hindering further approaches to industrial applications. This paper gives a perspective on these challenges from a Process Systems Engineering (PSE) standpoint, while at the same time highlighting the opportunities for advancements in the field in the European context. The challenges are connected with: the coupling of these processes with renewable electricity generation; the feedstock (in particular CO2); the processes itself; and the different products that can be obtained. PSE can determine the optimal interactions among the components of such systems, allowing educated decision making in designing the best process configurations under uncertainty and constrains. The opportunities, on the other hand, stem from a stronger collaboration between the PSE and the experimental communities, from the possibility of integrating ECO2R into existing industrial productions and from process-wide optimisation studies, encompassing the whole production cycle of the chemicals to exploit possible synergies.

Electrochemical CO₂ reduction is a promising way of closing the carbon cycle while synthesizing useful commodity chemicals and fuels. One of the possible routes to scale up the process is CO₂ reduction at elevated pressure, as this is a way to increase the concentration of poorly soluble CO₂ in aqueous systems. Yet, not many studies focus on this route, owing to the inherent challenges with high-pressure systems, such as leaks, product quantification, and ease of operation. In this study, we use a high-pressure flow cell setup to investigate the impact of CO₂ pressure on the electrochemical performance of a copper foam electrode for CO₂ reduction within a pressure range of 1 to 25 bar. Our initial findings using a 0.5 M potassium bicarbonate (KHCO₃) electrolyte show a consistent improvement in selectivity towards CO₂ reduction products, with HCOOH being the dominant product. By conducting a systematic exploration of operating parameters including applied current density, applied CO₂ pressure, cation effect, and electrolyte concentration, the selectivity towards formate (HCOOH) is optimized, achieving a remarkable 70 % faradaic efficiency (FE) under moderate conditions of 25 bar in a 0.5 M cesium bicarbonate (CsHCO₃) electrolyte. Additionally, we report the synthesis of isopropanol with a FE of 11 % at the 25 bar in 0.5 M KHCO₃ which is the highest reported selectivity towards isopropanol on copper using a bicarbonate system.

Electrochemical CO₂ reduction in non-aqueous solvents is promising due to the increased CO₂ solubility of organic-based electrolytes compared to aqueous electrolytes. Here the effect of nine different salts in propylene carbonate (PC) on the CO₂ reduction product distribution of polycrystalline Cu is investigated. Three different cations (tetraethylammonium (TEA), tetrabutylammonium (TBA), and tetrahexylammonium (THA)) and three different anions (chloride (Cl), tetrafluoroborate (BF₄), and hexafluorophosphate (PF₆)) were used. Chronoamperometry and in-situ FTIR measurements show that the size of the cation has a crucial role in the selectivity. A more hydrophobic surface is obtained when employing a larger cation with a weaker hydration shell. This stabilizes the CO₂⁻ radical and promotes the formation of ethylene. CO₂ reduction in 0.7 M THACl/PC shows the highest hydrocarbon formation. Lastly, we hypothesize that the hydrocarbon formation pathway is not through C−C coupling, as the CO solubility in PC is very high, but through the dimerization of the COH intermediate.

In this study, the effect of halide anions on the selectivity of the CO₂ reduction reaction to CO was investigated in choline-based ethylene glycol solutions containing different halides (ChCl : EG, ChBr : EG, ChI : EG). The CO₂RR was studied using silver (Ag) and gold (Au) electrodes in a compact H-cell. Our findings reveal that chloride effectively suppresses the hydrogen evolution reaction and enhances the selectivity of carbon monoxide production on both Ag and Au electrodes, with relatively high selectivity values of 84 % and 62 %, respectively. Additionally, the effect of varying ethylene glycol content in the choline chloride-containing electrolyte (ChCl : EG 1 : X, X=2, 3, 4) was investigated to improve the current density during CO₂RR on the Ag electrode. We observed that a mole ratio of 1 : 4 exhibited the highest current density with a comparable faradaic efficiency toward CO. Notably, an evident surface reconstruction process took place on the Ag surface in the presence of Cl⁻ ions, whereas on Au, this phenomenon was less pronounced. Overall, this study provides new insights into anion-induced surface restructuring of Ag and Au electrodes during CO₂RR, and its consequences on the reduction performance on such surfaces in non-aqueous electrolytes.

Extending the lifetime of electrocatalytic materials is a major challenge in electrocatalysis. Here, we employ atomic layer deposition (ALD) to coat the surface of carbon black supported platinum nanoparticles (Pt/CB) with an ultra-thin layer of silicon dioxide (SiO2) to prevent deactivation of the catalyst during H2 evolution. Our results show that after an accelerated durability test (ADT) the current density at −0.2 V vs. reversible hydrogen electrode (RHE) of the unprotected Pt/CB catalyst was reduced by 34%. By contrast, after coating the Pt/CB catalyst with 2 SiO2 ALD cycles, the current density at the same potential was reduced by 7% after the ADT procedure, whereas when the Pt/CB sample was coated with 5 SiO2 ALD cycles, the current density was reduced by only 2% after the ADT. Characterization of the Pt particles after electrochemical testing shows that the average particle size of the uncoated Pt/CB catalyst increases by roughly 16% after the ADT, whereas it only increases by 3% for the Pt/CB catalyst coated with 5 cycles of SiO2 ALD. In addition, the coating also strongly reduces the detachment of Pt nanoparticles, as shown by a strong decrease in the Pt concentration in the electrolyte after the ADT. However, 20 cycles of SiO2 ALD coating results in an over-thick coating that has an inhibitory effect on the catalytic activity. In summary, we demonstrate that only a few cycles of SiO2 ALD can strongly improve the stability of Pt catalyst for the hydrogen evolution reaction.

Carbon dioxide (CO2) electrolysis on copper (Cu) catalysts has attracted interest due to its direct production of C2+ feedstocks. Using the knowledge that CO2 reduction on copper is primarily a tandem reaction of CO2 to CO and CO to C2+ products, we show that modulating CO concentrations within the liquid catalyst layer allows for a C2+ selectivity of >80% at 200 mA cm−2 under broad conversion conditions. The importance of CO pooling is demonstrated through residence time distribution curves, varying flow fields (serpentine/parallel/interdigitated), and flow rates. While serpentine flow fields require high conversions to limit CO selectivity and maximize C2+ selectivity, the longer CO residence times of parallel flow fields achieve similar selectivity over broad flow rates. Critically, we show that parts of the catalyst area predominantly reduce CO instead of CO2 as supported by CO reduction experiments, transport modelling, and achieving a CO2 utilization efficiency greater than the theoretical limit of 25% for C2+ products.

Electrolytic bicarbonate conversion holds the promise to integrate carbon capture directly with electrochemical conversion. Most research has focused on improving the faradaic efficiencies of the system, however, the stability of the system has not been thoroughly addressed. Here, we find that the bulk electrolyte pH has a large effect on the selectivity, where a higher pH results in a lower selectivity. However, the bulk electrolyte pH has no effect on the stability of the system. A decrease in CO selectivity of 30 % was observed within the first three hours of operation in an optimized system with 3 M KHCO₃ and gap between the membrane and electrode. Single-pass electrolyte experiments at various constant pH values (8.5, 9.0, 9.5, and 10.0), show that only at a pH of 10 the CO selectivity was stable during three hours, reaching a faradaic efficiency toward CO of only 18 % as compared to an initial 55 % at pH 8.5. Trace metal impurities present in the electrolyte were found to be the cause of the decrease in stability as these deposit on the electrode surface. By complexing the trace metal ions with ethylenediaminetetraacetic acid (EDTA), the metal deposition was avoided and a stable CO selectivity was obtained.

The analytical tools to quantify CO₂RR products are often slow and have high limits of detection. As a result, researchers are forced to extend the duration of their experiments to accumulate sufficient product and surpass these detection limits. This slows down research considerably, and the research scope often remains limited. To help speed up CO₂RR catalyst studies, we have developed a new differential electrochemical mass spectrometer (DEMS) setup and cell design that enables the quantification of major gaseous and liquid products significantly faster than conventional analytical techniques. Special attention was given to the hydrodynamics of the cell to avoid mass transfer limitations and the calibration of the setup to accurately quantify the major CO₂ reduction products. As proof of concept of the methodology, the products formed during CO₂RR on a polycrystalline Ag and Cu electrode in a 0.1-M KHCO₃ electrolyte at different potentials were measured and quantified.

Electrochemical ammonia synthesis via the nitrogen reduction reaction (NRR) has been poised as one of the promising technologies for the sustainable production of green ammonia. In this work, we developed extensive process models of fully integrated electrochemical NH ₃ production plants at small scale (91 tonnes per day), including their techno-economic assessments, for (Li-)mediated, direct and indirect NRR pathways at ambient and elevated temperatures, which were compared with electrified and steam-methane reforming (SMR) Haber-Bosch processes. The levelized cost of ammonia (LCOA) of aqueous NRR at ambient conditions only becomes comparable with SMR Haber-Bosch at very optimistic electrolyzer performance parameters (FE > 80% at j ≥ 0.3 A cm ⁻²) and electricity prices (<$0.024 per kW h). Both high temperature NRR and Li-mediated NRR are not economically comparable within the tested variable ranges. High temperature NRR is very capital intensive due the requirement of a heat exchanger network, more auxiliary equipment and an additional water electrolyzer (considering the indirect route). For Li-mediated NRR, the high lithium plating potentials, ohmic losses and the requirement for H ₂, limits its commercial competitiveness with SMR Haber-Bosch. This incentivises the search for materials beyond lithium.

In this study, we experimentally screen a promising class of intermetallic alloys for the electrochemical reduction of CO₂ toward hydrocarbon products. Based on previous DFT-based screening papers, combinations of strongly CO-binding metals such as iron, cobalt, and nickel with weakly CO-binding metals such as gallium, aluminium or zinc were selected as potentially promising catalytic materials. Despite the challenging production of these alloys, we report a general two-step synthesis method for intermetallic alloys and discuss the specific synthesis conditions that must be taken into account when synthesising these materials. After their synthesis, we use a recently developed differential electrochemical mass spectrometry (DEMS) setup to rapidly quantify the CO₂ reduction products over a range of potentials. Almost all newly developed intermetallic catalysts are shown to produce methane and ethylene, while the CoSn catalyst showed higher selectivity towards formate production. However, all tested catalysts mostly produced hydrogen and only reduce CO₂ to a small extent, despite the favourable computational screening results. We discuss possible reasons for this discrepancy and outline a more holistic approach for linking future DFT studies with experiments.

Aqueous electrolytes used in CO2 electroreduction typically have a CO2 solubility of around 34 mM under ambient conditions, contributing to mass transfer limitations in the system. Non-aqueous electrolytes exhibit higher CO2 solubility (by 5–8-fold) and also provide possibilities to suppress the undesired hydrogen evolution reaction (HER). On the other hand, a proton donor is needed to produce many of the products commonly obtained with aqueous electrolytes. This work investigates the electrochemical CO2 reduction performance of copper in non-aqueous electrolytes based on dimethylformamide (DMF), n-methyl-2-pyrrolidone (NMP), and acetonitrile (ACN). The main objective is to analyze whether non-aqueous electrolytes are a viable alternative to aqueous electrolytes for hydrocarbon production. Additionally, the effects of aqueous/non-aqueous anolytes, membrane, and the selection of a potential window on the electrochemical CO2 reduction performance are addressed in this study. Experiments with pure DMF and NMP mainly produced oxalate with a faradaic efficiency (FE) reaching >80%; however, pure ACN mainly produced hydrogen and formate due to the presence of more residual water in the system. Addition of 5% (v/v) water to the non-aqueous electrolytes resulted in increased HER and formate production with negligible hydrocarbon production. Hence, we conclude that aqueous electrolytes remain a better choice for the production of hydrocarbons and alcohols on a copper electrode, while organic electrolytes based on DMF and NMP can be used to obtain a high selectivity toward oxalate and formate.

Selective ion separation is a fundamental challenge with applications ranging from the manufacturing of pharmaceuticals & industrial salts to water desalination. In particular, the separation of formate, a primary product of electrochemical carbon dioxide reduction, has attracted attention not only to reduce carbon emissions and energy costs but to provide new routes to value-added chemicals. In the present study, selective formate separation from an aqueous solution is demonstrated using an electrochemical flow cell with symmetric redox-active polyvinyl ferrocene electrodes. An electrosorption system equipped with an electrosorption cell, inline conductivity, and pH sensors was constructed to provide real-time measurements of the formate adsorption performance in continuous flow mode while varying operating conditions such as the flow rate, cell voltage, and electrolyte concentration. These parameters were optimized using a Box–Behnken experimental design to improve the formate adsorption selectivity. The flow cell results showed a selectivity higher than 6.0 toward the removal of formate in an electrolyte containing a 30-fold excess of perchlorate under optimal operation conditions (i.e., 0.5 mL/min flow rate, 1.0 V, and 15 mM electrolyte concentration). The performance of the flow cell was also tested using a solution that contained different liquid CO₂ reduction products, and formate separation was achieved. The results suggest that the proper design of the electrochemical cell and efficient operation of the flow platform pave the way for scaling up the technology for selective formate separation.

Nitrogen-doped (N-doped) carbon catalysts have been widely studied for electrochemical CO₂ reduction to CO. However, the correlation between the physicochemical properties of N-doped carbon catalysts and their electrocatalytic performance for the CO₂RR is still unclear. Herein, a series of N-doped biochar catalysts with different physicochemical properties were synthesized by tuning the carbonization temperature and N-doping level and used for the CO₂RR to analyze the structure-performance relationship. The prepared catalysts exhibited massive differences in maximum faradaic efficiency to CO from 26.8 to 94.9% at around −0.8 to −0.9 V vs RHE. In addition, we find that simply increasing the specific surface area and N-doping level of the catalysts does not effectively improve the catalytic performance for the CO₂RR. A multivariate correlation analysis reveals a negative correlation between the N-doping content and the electrochemical performance. The porous structural properties exhibit a positive correlation to the FE_CO but almost no correlation to j_CO. Interestingly, improving the degree of graphitization, surface hydrophobicity, the abundance of defects, and optimizing the porosity of the N-doped biochar catalyst can efficiently enhance the catalytic performance for the CO₂RR. We conclude that comprehensively analyzing the synergistic effect of various properties of N-doped biochar is critical to reveal structure-activity relationships.

Electrochemical CO₂ capture is promising for closing the carbon cycle but needs technological advances. In a recent issue of Nature Energy, a novel chemistry for electrochemical CO₂ capture is presented, demonstrating low energy consumption and high purity with virtually no degradation. This finally allows competition with amine-based capture technology.