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1. Modifying Copper Local Environment with Electrolyte Additives to Alter CO ₂ Electroreduction vs Hydrogen Evolution

   https://doi.org/10.1021/acscatal.3c00035  

   Sharifi_Golru, Samaneh; May, Andrew S; Biddinger, Elizabeth J (June 2023, ACS Catalysis)

   CO2 electroreduction (CO2ER) by using renewable energy resources is a promising method to mitigate the CO2 level in the atmosphere as well as producing valuable chemicals. Local environment at the electrode-electrolyte interface plays a key role in CO2ER activity and selectivity along with its competing hydrogen evolution reaction (HER). In addition to the catalyst and reactor design, electrolyte has also a significant impact on the interface. Herein, electrolyte additives were used to modify the local environment around the Cu catalyst during CO2ER. To this purpose, 10mM of ionic additives with bis(trifluoromethylsulfonyl)imide ([NTF2]-) and dicyanamide ([DCA]-) as anions and 1-butyl-3-methylimidazolium ([BMIM]+), potassium (K+), or sodium (Na+) as cations have been added to an aqueous potassium bicarbonate solution (0.1 M KHCO3). COMSOL Multiphysics was also used to calculate the local pH and CO2 concentration at electrode-electrolyte interface in different electrolytes. Results showed that the local environment modifications by the electrolyte additives altered the activity and selectivity of Cu in CO2ER. It was found that the CO2ER activity at -0.92 V was enhanced when using anion with high CO2 affinity and high hydrophobicity such as [NTF2]–. Among [NTF2]–-based additives, [BMIM][NTF2] had a higher faradaic efficiency (FE) for formate (38.7%) compared to K[NTF2] (23.2%) and Na[NTF2] (18.5%) at -0.92 V likely due to the presence of imidazolium cation which can further stabilize the intermediates on the surface and enhance CO2ER. Electrolytes containing [DCA]–-based additives with high hydrophilicity and low CO2 affinity had a very high HER selectivity (>90% FEH2) and low CO2ER selectivity regardless of the cation nature. This observation is attributed to the presence of hydrophilic [BMIM][DCA] in the vicinity of the catalyst which impacts the microenvironment around the catalyst. We observed that [DCA]– anions have a high affinity to adsorb on Cu catalysts as soon as the catalyst is submerged in the electrolyte. Although FTIR showed that [DCA]– anions desorb from the surface at negative potentials, it is likely that [DCA]– anions still remain in the proximity of the electrode, next to the adsorbed cations, impacting the transport of H2O and CO2, and altering the product selectivity. COMSOL calculations showed that the local pH is directly proportional to the H2 evolution activity. Also, hydrophilic salts such as those with the [DCA]– anion had a more alkaline local pH which leads to a lower CO2 concentration in the vicinity of the catalyst. 

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2. Tetraethylammonium Cation Activates Fe for Selective Electroreduction of CO ₂ to Oxalate

   https://doi.org/10.1002/celc.202500093  

   Sartape, Rohan; Chauhan, Rohit; Yadavalli, Venkata_S_R P; Goyal, Ishita; Amos, Ishaku; Qi, Yancun; Gande, Vamsi V; Sarkar, Abdul M; Glusac, Ksenija D; Singh, Meenesh R (May 2025, ChemElectroChem)

   The strong binding energy of CO on iron surfaces has rendered Fe electrodes as poor electrochemical CO₂reduction (eCO2R) catalysts, predominantly producing hydrogen. Recent studies on tuning the microenvironment near the catalyst surfaces by tuning the local electric field in nonaqueous environments have been shown to promote eCO2R by facilitating the CO₂activation step. Herein, the use of tetraethylammonium (TEA) cation to tune the electric field on Fe surfaces, such that it leads to the formation of industrially relevant oxalates (C₂products), is reported. At optimal cation concentrations, the developed eCO2R system achieves 25 mA cm⁻²of current density and Faradaic Efficiencies up to 75% toward oxalate. Furthermore, in situ attenuated total reflectance Fourier transform infrared spectroscopy indicates the presence of surface‐adsorbed TEA cations and other species on the Fe surfaces, leading to the well‐known outer‐sphere mechanism of electron transfer during eCO2R. The employment of Fe, along with microenvironment tuning, not only demonstrates high catalytic performance but also provides a safer and more sustainable alternative to toxic catalysts such as Pb that dominate the nonaqueous eCO₂R literature. These findings pave the way for further optimization and scale‐up of the process, offering a viable route for sustainable chemical production and CO₂mitigation. 

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3. Electrochemical oxygen reduction to hydrogen peroxide at practical rates in strong acidic media

   https://doi.org/10.1038/s41467-022-30337-0  

   Zhang, Xiao; Zhao, Xunhua; Zhu, Peng; Adler, Zachary; Wu, Zhen-Yu; Liu, Yuanyue; Wang, Haotian (December 2022, Nature Communications)

   Abstract Electrochemical oxygen reduction to hydrogen peroxide (H 2 O 2 ) in acidic media, especially in proton exchange membrane (PEM) electrode assembly reactors, suffers from low selectivity and the lack of low-cost catalysts. Here we present a cation-regulated interfacial engineering approach to promote the H 2 O 2 selectivity (over 80%) under industrial-relevant generation rates (over 400 mA cm −2 ) in strong acidic media using just carbon black catalyst and a small number of alkali metal cations, representing a 25-fold improvement compared to that without cation additives. Our density functional theory simulation suggests a “shielding effect” of alkali metal cations which squeeze away the catalyst/electrolyte interfacial protons and thus prevent further reduction of generated H 2 O 2 to water. A double-PEM solid electrolyte reactor was further developed to realize a continuous, selective (∼90%) and stable (over 500 hours) generation of H 2 O 2 via implementing this cation effect for practical applications. 

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4. Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO ₂ Reduction to Methanol

   https://doi.org/10.1002/anie.202310623  

   Rooney, Conor L; Lyons, Mason; Wu, Yueshen; Hu, Gongfang; Wang, Maoyu; Choi, Chungseok; Gao, Yuanzuo; Chang, Chun‐Wai; Brudvig, Gary W; Feng, Zhenxing; et al (January 2024, Angewandte Chemie International Edition)

   Abstract Many metal coordination compounds catalyze CO₂electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate methanol. The underlying structure–reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X‐ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc‐catalyzed CO₂reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi‐electron CO₂reduction. CO, the key intermediate in the CO₂‐to‐methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO₂for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza‐N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X‐ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non‐centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co−CO adduct during the catalysis. 

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5. NMR Study of CO ₂ Capture by Butylamine and Oligopeptide KDDE in Aqueous Solution: Capture Efficiency and Gibbs Free Energy of the Capture Reaction as a Function of pH**

   https://doi.org/10.1002/cphc.202300053  

   Yang, Kaidi; Schell, Joseph; Gallazzi, Fabio; Wycoff, Wei; Glaser, Rainer (June 2023, ChemPhysChem)

   Abstract We have been interested in the development of rubisco‐based biomimetic systems for reversible CO₂ capture from air. Our design of the chemical CO₂ capture and release (CCR) system is informed by the understanding of the binding of the activator CO₂(^ACO₂) in rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase). The active site consists of the tetrapeptide sequence Lys‐Asp‐Asp‐Glu (or KDDE) and the Lys sidechain amine is responsible for the CO₂ capture reaction. We are studying the structural chemistry and the thermodynamics of CO₂ capture based on the tetrapeptide CH₃CO−KDDE−NH₂ (“KDDE”) in aqueous solution to develop rubisco mimetic CCR systems. Here, we report the results of ¹H NMR and ¹³C NMR analyses of CO₂ capture by butylamine and by KDDE. The carbamylation of butylamine was studied to develop the NMR method and with the protocol established, we were able to quantify the oligopeptide carbamylation at much lower concentration. We performed a pH profile in the multi-equilibrium system and measured amine species and carbamic acid/carbamate species by the integration of ¹H NMR signals as a function of pH in the range 8 ≤ pH ≤ 11. The determination of ΔG₁(R) for the reaction R−NH₂ + CO₂ R−NH−COOH requires the solution of a multi‐equilibrium equation system, which accounts for the dissociation constants K₂ and K₃ controlling carbonate and bicarbonate concentrations, the acid dissociation constant K₄ of the conjugated acid of the amine, and the acid dissociation constant K₅ of the alkylcarbamic acid. We show how the multi‐equilibrium equation system can be solved with the measurements of the daughter/parent ratio X, the knowledge of the pH values, and the initial concentrations [HCO₃⁻]₀ and [R‐NH₂]₀. For the reaction energies of the carbamylations of butylamine and KDDE, our best values are ΔG₁(Bu) = −1.57 kcal/mol and ΔG₁(KDDE) = −1.17 kcal/mol. Both CO₂capture reactions are modestly exergonic and thereby ensure reversibility in an energy‐efficient manner. These results validate the hypothesis that KDDE‐type oligopeptides may serve as reversible CCR systems in aqueous solution and guide designs for their improvement. 

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