Alkali Cations Research Articles

Amino-functionalization enhanced CO2 reduction reaction in pure water.

The electrochemical reduction of carbon dioxide (CO2RR) to carbon monoxide represents a cost-effective pathway towards realizing carbon neutrality. To suppress the hydrogen evolution reaction (HER), the presence of alkali cations is critical, which can however lead to precipitate formation on the electrode, adversely impacting the device stability. Employing pure water as the electrolyte in zero-gap CO2 electrolyzers can address this challenge, albeit at the cost of diminished catalyst performance due to the absence of alkali cations. In this study, we introduce a novel approach by implementing amino modifications on the catalyst surface to mimic the function of alkali metal cations, while simultaneously working in pure water. This modification enhances the adsorption of carbon dioxide and protons, thereby facilitating the CO2RR while concurrently suppressing the HER. Utilizing this strategy in a zero-gap CO2 electrolyzer with pure water as the anolyte resulted in an impressive carbon monoxide faradaic efficiency (FECO) of 95.5% at a current density of 250 mA cm-2, while maintaining stability for over 180 hours without any maintenance.

Crystal structures of potassium and cesium salts of adenine: the role of alkali cations.

This study reports the crystal structures of potassium and cesium salts of adenine (K-adenine and Cs-adenine) in perspective of the interaction of alkali cations with purine nucleobases. Unlike previously-known guanine...

Electrolyte Engineering for Improved Selectivity of Electrochemical CO2 Reduction

Electrochemical CO2 reduction reaction (eCO2RR) offers a promising solution to produce valuable chemical building blocks especially when coupled with renewable energy sources. However, its practical application faces significant challenges including low production selectivity due to competing hydrogen evolution reactions (HER). As both reactions are highly sensitive to the chemical environment formulated around active sites within electrochemical double layer (EDL), a comprehensive understanding is required on the role of electrolyte components, such as cation, anion, local pH, and water molecules, in tailoring chemical environment and thereby determining selectivity between eCO2RR and HER kinetics on the same catalyst surface.In this context, recent studies have shown that electrolyte engineering can largely control eCO2RR/HER selectivity.[2,3] For instance, different alkali cations have been shown to largely determine CO2 conversion kinetics due to their different hydrated structure within EDL structures.[4] Moreover, an increased cation population within EDL can promote effective eCO2RR over HER even under highly acidic conditions through charge screening effect.[5] Nevertheless, a lack of dynamic information from conventional experimental approaches (e.g. gas chromatography-mass spectrometry) is largely limiting our efforts to comprehensively understand electrolyte engineering effects. To advance our knowledge in electrolyte engineering for high eCO2RR selectivity, it is essential to investigate the functional correlation between electrolyte properties and eCO2RR/HER competition occurring at the electrochemical interface in operando manner.[6,7] In this work, we utilized in situ Differential Electrochemical Mass Spectrometry (DEMS) to monitor the effects of various electrolyte engineering on eCO2RR/HER selectivity in a dynamic manner. Based on the online collection of product molecules and CO2 from Au catalyst surface, in situ DEMS can provide detailed information on both reaction competition between eCO2RR and HER and local CO2 concentration on catalyst surface on electrified catalyst surface. Based on the strength of in situ DEMS analysis, the critical role of electrolyte components will be addressed in terms of eCO2RR/HER kinetics and the local chemical environment. Overall, this work will highlight importance of understanding specific role of electrolyte engineering toward designing efficient eCO2RR systems for carbon-neutral energy technology.[1] A. Wagner, C. D. Sahm, and E. Reisner, Nat. Catal. 2020, 3, 775–786.[2] J. C. Bui, C. Kim, A. J. King, O. Romiluyi, A. Kusoglu, A. Z. Weber, and A. T. Bell, Acc. Chem. Res. 2022, 55, 484-494.[3] G. Marcandalli, M. C. O. Monteiro, A. Goyal, and M. T. M. Koper, Acc. Chem. Res. 2022, 55,1900-1911.[4] M. C. O. Monteiro, F. Dattila, B. Hagedoorn, R. Garcia-Muelas, N. Lopez, and M. T. M. Koper, Nat. Catal. 2021, 4, 654-662.[5] J. Gu, S. Liu, W. Ni, W. Ren, S. Haussener, and X. Hu, Nat. Catal. 2022, 5, 268-276.[6] A. Goyal, G. Marcandalli, V. A. Mints, and M. T. M. Koper, J. Am. Chem. Soc. 2020, 142, 4154-4161[7] E. L. Clark and A. T. Bell, J. Am. Chem. Soc. 2018, 140, 7012-7020.

Doping Strategy to Improve the Electrochemical Behavior of Lithium Rich Transition Metal Oxides As Cathodes for Lithium-Ion Batteries

Lithium-rich transition metal oxides are considered a promising cathodic solutions in Li-ion batteries to meet the growing energetic demand, thanks to their high specific capacity and operational voltage [1-2]. Li-rich layered materials have a general stoichiometry Li1+xTM1-xO2, in which TM is a blend of transition metals, as Ni, Mn, Co [2]. They stand out due to their high lithium concentration and specific capacity [1-2]. The higher capacity of Lithium-Rich can be attributed to the specific anionic redox reaction in the bulk at above 4.5 V. Nevertheless, large irreversible capacity loss in the first cycle, poor rate capability, mean working potential decay upon cycling and cobalt content are still major drawbacks that are hindering commercialization. In order to make these materials up scalable to industrial production, it is important to consider the reduction of costs and the toxicity of raw materials, in particular cobalt. Cobalt reduction has been identified as major driver to improve the environmental benignity of batteries and the sustainability of the overall production-consumption-recycling lifecycle. Several efforts to reduce these problems have been made, including the development of different synthetic strategies, doping and surface modification. The most, widely explored, chemical strategy to mitigate the voltage decay and structural degradation in Lithium Rich cathodes is the doping. Elemental doping can be divided into cation and anion doping. As an example, incorporation of redox inactive metals, such as Al, Zr, Ti, has been proposed in order to stabilize the lattice as well as the partial replacement of lithium ions with other alkali cations, e.g. K and Na; or doping the oxygen anion sublattice. In this communication, we present our doping approaches. In particular, the simultaneous replacement of cobalt in the layered structure with aluminum and lithium (over-lithiation). Moreover, we present over-lithiated Co-free materials where the introduction of different amount of iron has been investigated. The characterization of these novel layered materials is reported in terms of composition, structure, morphology and electrochemical performances. These approaches can be applied as a strategy to mitigate the voltage decay and reduce the Cobalt content.[1] Ji, X. et al. Journal of Power Sources 487, (2021).[2] Zhao, S. et al. Angewandte Chemie - International Edition 60, 2208–2220 (2021).

NHC Carbene-Metal Complex Ligand Binding Energies.

The ligand binding energies (LBEs) of N-heterocyclic carbenes (NHCs) and CH2 and CF2 adducts with group 1, 2, 10, and 11 metals and complexes with metals from these groups are predicted at the coupled cluster CCSD(T) level of theory by using density functional theory optimized geometries. The differences in LBEs as a function of the metal and the types of bonding interactions as well as the type of carbene are described. The bonding between the alkali cations and alkaline earth dications is predominantly ionic with a linear correlation between the LBEs and the cation hardness. In contrast, the bonding behaviors of the group 10 and 11 metals and metal complexes have only a weak, indirect correlation between the LBEs and the metal hardness. The difference in bonding behavior between the groups of metals arises due to the accessibility of electron donation between the ligand and the metal in the transition metal complexes, which results in more covalent-like bonding behavior. The presence of the methyl groups on the NHC nitrogen results in only slightly more delocalized charge from the metal onto the ring, but there is significant redistribution of the charge on the ring. Saturation of the NHC ring had a much smaller effect on how the charge was distributed on the ring. The analysis of the bonding behavior of NHCs with various metal groups enables improved understanding of carbene-metal interactions to inform rational design of NHC-based systems.

Stable WO3 electrochromic system based on NH4+ hydrogen bond chemistry

As the best-known and extensively-studied electrochromic material, tungsten trioxide (WO3) has drawn tremendous interest due to its low material cost, environmental benignity, dual band regulation, high optical modulation, and high chemical stability. However, these films always suffer from ion-trapping-induced degradation in electrochromic performance when cycled in alkali cation (such as Li+, Na+, K+, etc.) electrolytes. Herein, we report a stable WO3 electrochromic system enabled by a NH4CF3SO3-TEP (Triethyl phosphate) organic electrolyte. Based on comparative experiments and systematic characterizations, the prolonged cycling stability is mainly attributed to the formation of hydrogen bonds between the NH4+ ions and the WO3 lattice, which are much weaker than metallic coordination bonds. Furthermore, the bulky CF3SO3− anion and large TEP solvent molecule are also favorable to stabilize WO3, since they are more resistive to be co-inserted into the WO3 lattice along with the shuttling NH4+ cations. Thanks to these merits, this NH4CF3SO3-TEP electrolyte simultaneously enables great electrochromic activity (76.1 % transmittance modulating ability at 633 nm) and impressive cyclic color-switching stability (1000 times color change without any detectable electrochromic performance or mechanical degradation), overwhelmingly outperforming the conventional Li+/K+ electrolytes. Furthermore, as a demonstration of its application, a WO3/Zn electrochromic device is fabricated based on a NH4+/Zn2+-CF3SO3 dual-cation TEP electrolyte. These findings may shed light on the in-depth understanding of WO3′s “ion trapping” effect, as well as the electrolyte design of high-performance WO3-based electrochromic devices.

Carbon Monoxide Reduction Reaction to Produce Multicarbon Products in Acidic Electrolytes Using Gas Diffusion Electrode Loaded with Copper Nanoparticles

AbstractThe synthesis of multi‐carbon products (C2+) by electrochemical CO2 reduction reaction (CO2RR) is a promising technology that will contribute to the realization of a carbon‐neutral society. In particular, efficient CO2RR to produce C2+ in acidic electrolytes is desirable because the conversion of CO2 to inert (bi)carbonate can be suppressed under acidic conditions, thereby increasing the efficiency of substrate CO2 utilization. Herein, since C2+ products are produced via the dimerization of carbon monoxide, an intermediate in CO2RR, the focus is on the carbon monoxide reduction reaction (CORR). A gas diffusion electrode loaded with copper nanoparticles is used in acidic electrolytes to investigate the conditions necessary for efficient C2+ production. The faradaic efficiency and partial current density for C2+ production attained 75% and 280 mA cm−2 in a pH 2.0 solution, and they reached up to 66% and 260 mA cm−2 even in a pH 1.0 solution. Numerical simulations showed that increasing the alkalinity of the electrode surface to greater than pH 7 by consuming protons is necessary to facilitate the production of C2+ during the CORR. When the desired level of alkalinity is achieved, the concentration and type of alkali cations present at the electrode surface have an impact on the selectivity for C2+ production.

Formation of Neptunium(V) Carbonates: Examining the Forceful Influence of Alkali and Alkaline Earth Cations.

Herein, neptunium(V) carbonates containing sodium or potassium cations were synthesized via chemical precipitation. Various techniques such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetry combined with differential scanning calorimetry, X-ray diffraction, and X-ray absorption spectroscopy were used to analyze the microstructures and elemental compositions of these samples. The crystal structures of hydrated NaNpO2CO3·3H2O (P1, a = 4.3420(2) Å, b = 4.8962(2) Å, c = 10.0933(11) Å, α = 91.014(7)°, β = 77.834(11)°, and γ = 90.004(10)°) and KNpO2CO3 (P63/mmc, a = b = 5.0994(2) Å, c = 10.2210(15) Å) were determined for the first time using the Rietveld method. The synthesized carbonates exhibited distinct structural features and decomposition behaviors, as demonstrated through thermogravimetry analysis, which revealed the presence of crystalline hydrate water in sodium neptunium(V) carbonate. Furthermore, calcium-containing neptunium(V) carbonates were synthesized and characterized. Samples with the general composition Ca0.5NpO2CO3 were obtained using the ion exchange method and chemical precipitation from solutions containing competing cations (Ca2+, Na+, K+, and Mg2+). The synthesis conditions notably affected the diffraction patterns of the obtained calcium neptunium(V) carbonates. This investigation enhances our understanding of the structural properties and thermodynamic stability of neptunium(V) carbonates in the presence of diverse cations commonly found under radioactive waste disposal conditions.

Alkali Metal Cation-Sulfate Anion Ion Pairs Promoted the Cleavage of C-C Bond During Ethanol Electrooxidation.

Direct ethanol fuel cells show great promise as a means of converting biomass ethanol derived from biomass into electricity. However, the efficiency of complete conversion is hindered by the low selectivity in breaking the C-C bond. This selectivity is determined by factors such as the material structure and reaction conditions, including the nature of the supporting electrolyte. Cations serve not only as facilitators of electricity conduction through ion migration but also as influencers of the reaction pathways. In this study, we utilized differential electrochemical mass spectrometry to track the in situ generation of CO2 during potential scanning. The presence of alkali cations led to an enhancement in the CO2 selectivity. In addition, in situ Raman spectroscopy provided evidence of the formation of alkali metal cation-sulfate anion ion pairs. The catalytic activity and CO2 selectivity were found to be directly correlated to the ionic strength of these ion pairs.

Evidence for Mixed Mg Coordination Environments in Silicate Glasses: Results from 25Mg NMR Spectroscopy at 35.2 T.

The Mg-O coordination environment of silicate glasses of composition CaMgSi2O6, Na2MgSi3O8, and K2MgSi5O12 is probed using ultrahigh-field (35.2 T) 25Mg magic angle spinning nuclear magnetic resonance (MAS NMR) and triple-quantum MAS NMR spectroscopy. These spectra clearly reveal the coexistence of 4-fold- (MgIV) and 6-fold- (MgVI) coordinated Mg in all glasses. The MgIV/MgVI ratio implies an average Mg-O coordination number of ∼5 for CaMgSi2O6 glass, bringing NMR results for the first time in good agreement with those reported in previous studies based on diffraction and X-ray absorption spectroscopy, thus resolving a decade-long controversy regarding Mg coordination in alkaline-earth silicate glasses. The Mg-O coordination number decreases to ∼4.5 in the alkali-Mg silicate glasses, indicating that Mg competes effectively with the low field strength alkali cations for the nonbridging oxygen in the structure to attain tetrahedral coordination. This work illustrates the promise of ultrahigh-field NMR spectroscopy in structural studies involving nuclides with low gyromagnetic ratio.

Assessing Precipitation Redistribution and Hydro-Chemical Dynamics in a High-Elevation Evergreen Broad-Leaved Forest

Forest water dynamics and hydro-chemical characteristics are essential for understanding forest hydrology and ecological processes. Yet, such understanding is limited by a lack of long-term monitoring data and observations from specialized forest ecosystems such as those from high elevation. Here, we analyze the precipitation redistribution including interception, stemflow, and throughfall and hydro-chemical characteristics by using a 15 year (2005–2019) precipitation dataset in a high elevation, evergreen broad-leaved forest in Southwest China. The forest experienced an obvious seasonal variation in precipitation with a monthly average of 117.31 ± 91.21 mm. The precipitation redistribution was influenced by precipitation intensity and leaf area index and differed inter-annually and intra-annually, with a general pattern: throughfall > canopy interception > stemflow. Throughfall rate increased significantly from 2015 to 2019 after experiencing the January 2015 snowstorm. The majority of water within the study site was retained in the soil and apoplastic materials. The primary means of water output was evapotranspiration, with minimal surface runoff. Quality of surface water was affected by the weathering of rocks, resulting in a lower pH than that of atmospheric precipitation. During the rainy season, elemental Ca and Mg showed negative correlation with precipitation due to plant mediation. The other elements, pH, total dissolved solids, precipitation, air temperature, and water temperature showed different degrees of correlation with each other. Overall, while the water balance fluctuated over the past 15 years, the water-holding capacity remained relatively stable. Alkali cations such as Ca2+, Mg2+, and K+ in the water body showed a decreasing trend during 2005–2019, which is a potential threat to ecological stability.

Synthesis and Structure of New Potassium and Cesium Zinc Diphosphates

This article presents the results of a study of new solid solutions formed in the system of diphosphates of alkaline elements and zinc: K2Zn3(P2O7)2–Cs2Zn3(P2O7)2. The obtained materials are promising as matrices for creating phosphors. The formation of phases containing two alkali cations is established on samples obtained by solid-phase synthesis by X-ray phase analysis, and the results of studying their thermal stability are presented.

Stabilization of Guest Molecules inside Cation-Lidded Cucurbiturils Reveals that Hydration of Receptor Sites Can Impede Binding.

Docking of alkali metal ions to water-soluble macrocyclic receptors generally reduces the affinity of guest molecules due to competitive binding. The idea that solvation water molecules could display a larger steric hindrance towards guest binding than cations has not been considered to date. We show that the docking of large cations to cucurbit[5]uril (CB5) unexpectedly increases (by a factor of 5-8) the binding of hydrophobic guests, methane and ethane. This is due to the removal of water molecules from the carbonyl portals of CB5 during cation binding, which frees up space for hydrophobe encapsulation. In contrast, smaller cations like sodium protrude deeply into the cavity of CB5 and cause the expected decrease in binding, such that the rational selection of alkali cations allows for a variation of up to a factor of 20 in binding of methane and ethane. The statistical analysis of crystallographic data shows that the cavity volume of CB5 can be enlarged by placing large alkali ions (Rb+ and Cs+ ) centro-symmetrically at the portals. The results reveal a hitherto elusive steric hindrance of solvation water molecules near receptor binding sites, which is pertinent for the design of supramolecular catalysts and the understanding of biological receptors.

Stabilization of Guest Molecules inside Cation‐Lidded Cucurbiturils Reveals that Hydration of Receptor Sites Can Impede Binding

AbstractDocking of alkali metal ions to water‐soluble macrocyclic receptors generally reduces the affinity of guest molecules due to competitive binding. The idea that solvation water molecules could display a larger steric hindrance towards guest binding than cations has not been considered to date. We show that the docking of large cations to cucurbit[5]uril (CB5) unexpectedly increases (by a factor of 5–8) the binding of hydrophobic guests, methane and ethane. This is due to the removal of water molecules from the carbonyl portals of CB5 during cation binding, which frees up space for hydrophobe encapsulation. In contrast, smaller cations like sodium protrude deeply into the cavity of CB5 and cause the expected decrease in binding, such that the rational selection of alkali cations allows for a variation of up to a factor of 20 in binding of methane and ethane. The statistical analysis of crystallographic data shows that the cavity volume of CB5 can be enlarged by placing large alkali ions (Rb+ and Cs+) centro‐symmetrically at the portals. The results reveal a hitherto elusive steric hindrance of solvation water molecules near receptor binding sites, which is pertinent for the design of supramolecular catalysts and the understanding of biological receptors.

Experimental research of alkali metals modified Mg/DOBDC metal organic framework as high capacity CO2 adsorbent

In this paper, novel M−Mg/DOBDC (M = Li, Na, K) composites (a MOF built of Mg(OAc)2·4H2O and MOAc (M = Li, Na, K) linked by 2,5-dioxido-1,4-benzenedicarboxylate (DOBDC) ligands) were prepared for the first time by doping alkali metals in Mg/DOBDC MOF. The CO2 dynamic adsorption performance of the novel synthesized composite was experimentally investigated, including different alkali metal doping amounts and alkali metal species. The structural morphology and CO2 adsorption of the composites were characterized by XRD, FT-IR, SEM, EDX, BET, CO2-TPD and TGA. Ten cycles of adsorption–desorption tests were performed on the M−Mg/DOBDC after doping with alkali metals. In addition, the CO2 adsorption process of the materials was simulated using various models. The results showed that the introduction of the alkali cation M+ would coordinate with the active site of the metal center and had high affinity and activation ability for CO2. The composite with the best dynamic CO2 uptake after the modification of Li, Na and K alkali metals was 0.5 K-Mg/DOBDC with an adsorption capacity of 14.93 mmol g−1 (0.1 MPa, 25 °C), which was 3.44 times higher than that of the parent material Mg/DOBDC. That was higher than the previously reported CO2 capture performance.

Cation Adaptive Structures Based on Manganese Cyanide Prussian Blue Analogues: Application of Powder Diffraction Data to Solve Complex, Unprecedented Stoichiometries and New Structure Types.

A Mn(II) salt and A+ CN- under anaerobic conditions react to form 2-D and 3-D extended structured compounds of Am MnII n (CN)m+2n stoichiometry. Here, the creation and characterization of this large family of compounds, for example AMnII 3 (CN)7 , A2 MnII 3 (CN)8 , A2 MnII 5 (CN)12 , A3 MnII 5 (CN)13 , and A2 MnII [MnII (CN)6 ], where A represents alkali and tetraalkylammonium cations, is reviewed. Cs2 MnII [MnII (CN)6 ] has the typical Prussian blue face centered cubic unit cell. However, the other alkali salts are monoclinic or rhombohedral. This is in accord with smaller alkali cation radii creating void space that is minimized by increasing the van der Waals stabilization energy by reducing ∠Mn-N≡C, which, strengthens the magnetic coupling and increases the magnetic ordering temperatures. This is attributed to the non-rigidity of the framework structure due the significant ionic character associated with the high-spin MnII sites. For larger tetraalkylammonium cations, the high-spin Mn sites lack sufficient electrostatic A+ ⋅⋅⋅NC stabilization and form unexpected 4- and 5-coordinated Mn sites within a flexible, extended framework around the cation; hence, the size, shape, and charge of the cation dictate the unprecedented stoichio-metry and unpredictable cation adaptive structures. Antiferromagnetic coupling between adjacent MnII sites leads to ferrimagnetic ordering, but in some cases antiferromagnetic coupling of ferrimagnetic layers are compensated and synthetic antiferromagnets are observed. The magnetic ordering temperatures for ferrimagnetic A2 MnII [MnII (CN)6 ] with both octahedral high- and low-spin MnII sites increase with decreasing ∠Mn-N≡C. The crystal structures for all of the extended structured materials were obtained by powder diffraction.

Sulfuric acid resistance behaviour of alkali-activated slag and waste glass powder blended precursors

The acid resistance of cementitious materials is an important property when exposed to aggressive acidic environments. In this study, the waste glass powder (GP) and slag as precursors were activated by alkali (Na or K)-silicates or by a combination of (Na or K)-silicates with air pollution control (APC) residues to produce alkali-activated materials (AAMs) and alkali/sulfate-activated materials (ASAMs). The compressive strength and volume change of the AAMs and ASAMs mortar were performed to understand the influence of sulfuric acid attack on the resulting performances. Meanwhile, the microstructure and micro-mechanics evolution were investigated by the nanoindentation technology. The results showed that the compressive strengths of all AAMs and ASAMs mortar decreased under a low pH solution. The Na- and K-AAMs mortar exposed to the acid solution shrank considerably even though a large amount of gypsum formed, while the Na- and K-ASAMs exhibited certain expansion behavior due to the existing sodium sulfate. Upon the sulfuric acid attack, the framework changes of the K-A-S-H/N-A-S-K caused by dealumination had less effect on the integrity than the dealumination and decalcification of the C(-A)-S-H gel. In comparing the alkali cations, the K-type activator impacted more positively than the Na-type activator for the performance development of the AAMs and ASAMs under the sulfuric acid attack. Moreover, the AAMs and ASAMs showed a buffering capacity of acid. This work provides a scientific reference value for applying the AAMs and ASAMs in real environments.

Dual‐Role of Polyelectrolyte‐Tethered Benzimidazolium Cation in Promoting CO2/Pure Water Co‐Electrolysis to Ethylene

AbstractElectrochemical CO2 reduction reaction (CO2RR), as a promising route to realize negative carbon emissions, is known to be strongly affected by electrolyte cations (i.e., cation effect). In contrast to the widely‐studied alkali cations in liquid electrolytes, the effect of organic cations grafted on alkaline polyelectrolytes (APE) remains unexplored, although APE has already become an essential component of CO2 electrolyzers. Herein, by studying the organic cation effect on CO2RR, we find that benzimidazolium cation (Beim+) significantly outperforms other commonly‐used nitrogenous cations (R4N+) in promoting C2+ (mainly C2H4) production over copper electrode. Cyclic voltammetry and in situ spectroscopy studies reveal that the Beim+ can synergistically boost the CO2 to *CO conversion and reduce the proton supply at the electrocatalytic interface, thus facilitating the *CO dimerization toward C2+ formation. By utilizing the homemade APE ionomer, we further realize efficient C2H4 production at an industrial‐scale current density of 331 mA cm−2 from CO2/pure water co‐electrolysis, thanks to the dual‐role of Beim+ in synergistic catalysis and ionic conduction. This study provides a new avenue to boost CO2RR through the structural design of polyelectrolytes.

Dual-Role of Polyelectrolyte-Tethered Benzimidazolium Cation in Promoting CO2/Pure Water Co-Electrolysis to Ethylene.

Electrochemical CO2 reduction reaction (CO2RR), as a promising route to realize negative carbon emissions, is known to be strongly affected by electrolyte cations (i.e., cation effect). In contrast to the widely-studied alkali cations in liquid electrolytes, the effect of organic cations grafted on alkaline polyelectrolytes (APE) remains unexplored, although APE has already become an essential component of CO2 electrolyzers. Herein, by studying the organic cation effect on CO2RR, we find that benzimidazolium cation (Beim+) significantly outperforms other commonly-used nitrogenous cations (R4N+) in promoting C2+(mainly C2H4) production over copper electrode. Cyclic voltammetry and in-situ spectroscopy studies reveal that the Beim+ can synergistically boost the CO2 to *CO conversion and reduce the proton supply at the electrocatalytic interface, thus facilitating the *CO dimerization toward C2+formation. By utilizing the homemade APE ionomer, we further realize efficient C2H4 production at an industrial-scale current density of 331 mA cm-2 from CO2/pure water co-electrolysis, thanks to the dual-role of Beim+ in synergistic catalysis and ionic conduction. This study provides a new avenue to boost CO2RR through the structural design of polyelectrolytes.

Probing Cation Effects on *CO Intermediates from Electroreduction of CO2 through Operando Raman Spectroscopy.

Cations in an electrolyte modulate microenvironments near the catalyst surface and affect product distribution from an electrochemical CO2 reduction reaction, and thus, their interaction with intermediate states has been tried to be probed. Herein, we directly observed the cation effect on *CO intermediates on the Cu(OH)2-derived catalyst in real time through operando surface-enhanced Raman spectroscopy at high overpotentials (-1.0 VRHE). Atop *CO peaks are composed of low-frequency binding *CO (*COLFB) and high-frequency binding *CO (*COHFB) because of their adsorption sites. These two *CO intermediates are found to have different sensitivities to the cation-induced field, and each *CO is proposed to be suitably stabilized for efficient C-C coupling. The proportions between *COHFB and *COLFB are dependent on the type of alkali cations, and the increases in the *COHFB ratio have a high correlation with selective C2H4 production under K+ and Cs+, indicating that *COHFB is the dominant and fast active species. In addition, as the hydrated cation size decreases, *COLFB is more sensitively red-shifted than *COHFB, which promotes C-C coupling and suppresses C1 products. Through time-resolved operando measurements, dynamic changes between the two *CO species are observed, showing the rapid initial adsorption of *COHFB and subsequently reaching a steady ratio between *COLFB and *COHFB.