Anne Co

The presence of alkali metal cations in the electrolyte substantially affects the reactivity and selectivity of electrochemical carbon dioxide (CO ₂ ) reduction (CO ₂ R). This study examines the role of cations in CO ₂ R on single-crystal and polycrystalline Au under controlled mass-transport conditions. It establishes that CO ₂ adsorption is the rate-determining step regardless of cation type or surface structure. Density functional theory calculations show that electron transfer occurs to a solvated CO ₂ -cation complex. A more positive potential of zero charge enhances CO ₂ R activity only on Au with similar surface coordination. The symmetry factor (β) of the rate-determining step varies with surface structure and cation identity, with density functional theory calculations indicating β’s sensitivity to surface and double-layer structures. These findings emphasize the importance of both surface and double-layer structures in understanding cation effects on CO ₂ R.

The presence of alkali metal cations in the electrolyte substantially affects the reactivity and selectivity of electrochemical carbon dioxide (CO ₂ ) reduction (CO ₂ R). This study examines the role of cations in CO ₂ R on single-crystal and polycrystalline Au under controlled mass-transport conditions. It establishes that CO ₂ adsorption is the rate-determining step regardless of cation type or surface structure. Density functional theory calculations show that electron transfer occurs to a solvated CO ₂ -cation complex. A more positive potential of zero charge enhances CO ₂ R activity only on Au with similar surface coordination. The symmetry factor (β) of the rate-determining step varies with surface structure and cation identity, with density functional theory calculations indicating β’s sensitivity to surface and double-layer structures. These findings emphasize the importance of both surface and double-layer structures in understanding cation effects on CO ₂ R.

Although many porous materials, including metal–organic frameworks (MOFs), have been reported to selectively adsorb C₂H₂ in C₂H₂/CO₂ separation processes, CO₂‐selective sorbents are much less common. Here, we report the remarkable performance of MFU‐4 (Zn₅Cl₄(bbta)₃, bbta=benzo‐1,2,4,5‐bistriazolate) toward inverse CO₂/C₂H₂ separation. The MOF facilitates kinetic separation of CO₂ from C₂H₂, enabling the generation of high purity C₂H₂ (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C₂H₂ is excluded from MFU‐4 by narrow pore windows formed by Zn−Cl groups. Postsynthetic F⁻/Cl⁻ ligand exchange was used to synthesize an analogue (MFU‐4‐F) with expanded pore apertures, resulting in equilibrium C₂H₂/CO₂ separation with reversed selectivity compared to MFU‐4. MFU‐4‐F also exhibits a remarkably high C₂H₂ adsorption capacity (6.7 mmol g⁻¹), allowing fuel grade C₂H₂ (98 % purity) to be harvested from C₂H₂/CO₂ mixtures by room temperature desorption.

Deoxygenation of aldehydes and their tautomers to alkenes and alkanes has implications in refining biomass-derived fuels for use as transportation fuel. Electrochemical deoxygenation in ambient, aqueous solution is also a potential green synthesis strategy for terminal olefins. In this manuscript, direct electrochemical conversion of vinyl alcohol and acetaldehyde on polycrystalline Cu to ethanol, ethylene and ethane; and propenol and propionaldehyde to propanol, propene and propane is reported. Sensitive detection was achieved using a rotating disk electrode coupled with gas chromatography-mass spectrometry. In-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy, and in-situ Raman spectroscopy confirmed the adsorption of the vinyl alcohol. Calculations using canonical and grand-canonical density functional theory and experimental findings suggest that the rate-determining step for ethylene and ethane formation is an electron transfer step to the adsorbed vinyl alcohol. Finally, we extend our conclusions to the enol reaction from higher-order soluble aldehyde and ketone. The products observed from the reduction reaction also sheds insights into plausible reaction pathways of CO₂ to C₂ and C₃ products.

Simulating photosynthesis has long been one of the ideas for realizing the conversion of solar energy into industrial chemicals. Heterogeneous N₂ photofixation in water is a promising way for sustainable production of ammonia. However, a mechanistic understanding of the complex aqueous photocatalytic N₂ reduction is still lacking. In this study, a light‐dependent surface hydrogenation mechanism and light‐independent protection of catalyst surface for N₂ reduction are revealed on ultrathin Bi₄O₅Br₂ (BOB) nanosheets, in which the creation and annihilation of surface bromine vacancies can be controlled via a surface bromine cycle. Our rapid scan in situ FT‐IR spectra verify that photocatalytic N₂ reduction proceeds through an associative alternating mechanism on BOB surface with bromine vacancies (BrV‐BOB). This work provides a new strategy to combine light‐dependent facilitated reaction with light‐independent regeneration of catalyst for advancing sustainable ammonia production.

Li distribution within the battery electrode material is quantified using neutron depth profiling (NDP) as a function of depth in real-time.

La_0.7Sr_0.2Ni_0.2Fe_0.8O₃ (LSNF), having thermochemical stability, superior ionic and electronic conductivity, and structural flexibility, was investigated as a cathode in SOECs.

Surface potential measurement values of the gas-liquid interface can be ambiguous despite the numerous electrochemical approaches used for quantification of the reported values. Calibration and normalization methods are not standardized, which often undermines the robustness of the reported values. Surface potential instrumentation and data interpretation also varies significantly across literature. Here, we propose a circuit model for an ionizing surface potential method based on the alpha decay of a radioactive americium-241 electrode. We evaluate the robustness of the circuit model for quantifying the surface potential at the air-aqueous interface. We then show successful validation of our circuit model through determination of the surface tension of the air-electrolyte interface with comparison to respective surface tension literature values. This validation reveals the reliability of surface potential measurements using the americium-241 ionizing method. We also report the surface potential difference of the air/water interface to be −0.49 V ± 0.01 V consistent with hydrogens of water pointing toward the air phase.

We report, for the first time, utilizing a rotating ring‐disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO₂ reduction reaction (CO₂RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by −86±2 mV/pH during CO₂RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO₂RR and find that during CO₂RR to CO on Au in an MHCO₃ buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li⁺ > Na⁺ > K⁺ > Cs⁺, which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO₂RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO₂RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO₂RR products have pH‐dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.

We report, for the first time, utilizing a rotating ring‐disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO₂ reduction reaction (CO₂RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by −86±2 mV/pH during CO₂RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO₂RR and find that during CO₂RR to CO on Au in an MHCO₃ buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li⁺ > Na⁺ > K⁺ > Cs⁺, which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO₂RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO₂RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO₂RR products have pH‐dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.

Here, we demonstrate that small molecules such as H₂, CO, HCOO⁻ and their mixtures, generated from the electroreduction of CO₂ (CO₂RR), can be detected and quantified on a rotating ring-disc electrode (RRDE). We describe a series of systematic calibration protocol to quantify CO₂RR products on four model electrocatalysts (Pt, Au, Sn, [Ni^II(cyclam)]²⁺). In an RRDE assembly, products generated at the disc are convectively transported and detected at the ring detector before diffusing into the bulk solution, circumventing the need for product pre-concentration. As the electrochemical fingerprints of these small molecules and their mixtures on the Pt detector are unique, RRDE also excludes the need for separation. Thus, using the rotating ring detector significantly minimizes the time delay between product generation and detection compared to conventional techniques such as GC, LC and NMR. An RRDE allows faster screening of catalysts that can help accelerate catalyst discovery for CO₂RR. It also enables time-dependent mechanistic studies of CO₂RR catalysis.

Here, we demonstrate that small molecules such as H₂, CO, HCOO⁻ and their mixtures, generated from the electroreduction of CO₂ (CO₂RR), can be detected and quantified on a rotating ring-disc electrode (RRDE). We describe a series of systematic calibration protocol to quantify CO₂RR products on four model electrocatalysts (Pt, Au, Sn, [Ni^II(cyclam)]²⁺). In an RRDE assembly, products generated at the disc are convectively transported and detected at the ring detector before diffusing into the bulk solution, circumventing the need for product pre-concentration. As the electrochemical fingerprints of these small molecules and their mixtures on the Pt detector are unique, RRDE also excludes the need for separation. Thus, using the rotating ring detector significantly minimizes the time delay between product generation and detection compared to conventional techniques such as GC, LC and NMR. An RRDE allows faster screening of catalysts that can help accelerate catalyst discovery for CO₂RR. It also enables time-dependent mechanistic studies of CO₂RR catalysis.

The hydrogenation of 5‐hydroxymethylfurfural (HMF), an important bio‐based platform chemical, to 2,5‐bis(hydroxymethyl)furan (BHMF), a promising building block for polymers, is conventionally conducted at high pressures of H₂ in the presence of heterogeneous catalysts. Recently, electrochemical hydrogenation has emerged as a promising process for BHMF production; however, one challenge of this process is to improve the catalytic activity of the electrocatalyst. In this study, a series of AgCu electrocatalysts was prepared by galvanic displacement of Ag on nanotextured Cu particles. A comprehensive characterization of the catalysts was carried out and the effects of electrolysis potential, reaction time, and HMF concentration were investigated. The concentration of AgNO₃ solution in which Cu was displaced was found to be a key factor to control the catalyst surface morphology, and the optimal catalyst was shown to have high catalytic activity and excellent stability for the electrochemical hydrogenation of HMF to BHMF.

The hydrogenation of 5‐hydroxymethylfurfural (HMF), an important bio‐based platform chemical, to 2,5‐bis(hydroxymethyl)furan (BHMF), a promising building block for polymers, is conventionally conducted at high pressures of H₂ in the presence of heterogeneous catalysts. Recently, electrochemical hydrogenation has emerged as a promising process for BHMF production; however, one challenge of this process is to improve the catalytic activity of the electrocatalyst. In this study, a series of AgCu electrocatalysts was prepared by galvanic displacement of Ag on nanotextured Cu particles. A comprehensive characterization of the catalysts was carried out and the effects of electrolysis potential, reaction time, and HMF concentration were investigated. The concentration of AgNO₃ solution in which Cu was displaced was found to be a key factor to control the catalyst surface morphology, and the optimal catalyst was shown to have high catalytic activity and excellent stability for the electrochemical hydrogenation of HMF to BHMF.

An approach to elucidate the capacity fade mechanism of Sn nanoparticles is demonstrated through operando⁷Li NMR,ex situ⁷Li magic-angle spinning NMR and pair distribution function methods.

An approach to elucidate the capacity fade mechanism of Sn nanoparticles is demonstrated through operando⁷Li NMR,ex situ⁷Li magic-angle spinning NMR and pair distribution function methods.

Nitrogen‐doped carbon nanostructures (CN_x) are promising cathode materials as catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane (PEM) fuel cells. Incorporation of chlorine into CN_x catalysts using a facile methodology can lead to a significant improvement in the ORR activity in acidic media, as confirmed by electrochemical half‐cell measurements. The chlorine‐containing CN_x catalyst (CN_x−Cl) is synthesized by soaking CN_x powder in 0.3 M HCl. The analysis of near‐edge X‐ray absorption fine structure spectra collected in the C K‐edge region and Fourier‐transform infrared spectra confirm the formation of C−Cl bonds in CN_x−Cl. X‐ray photoelectron spectroscopy (XPS) results reveal the presence of three distinct chlorine species in the CN_x−Cl sample: (i) organic chlorine (C−Cl), (ii) anionic chloride in the positively charged environment of a pyridinium ring (N⁺Cl⁻), and (iii) physisorbed ionic chloride. Results from temperature‐programmed desorption studies under inert atmosphere corroborate the conclusions from XPS depth profiling analysis. The improvement in ORR activity after exposure of the CN_x catalyst to chloride anions can be attributed to the creation of C−Cl functionalities as additional active sites. The difference in the electronegativity of C and Cl atoms results in a net positive charge on adjacent carbon sites, leading to the side‐on adsorption of oxygen molecules and breakage of the O−O bond during ORR.

dOp NMR resolves and differentiates formation and removal of LiC₇₂ to LiC₆ as well as previously undetected gas like GIC stages (precursors).

dOp NMR resolves and differentiates formation and removal of LiC₇₂ to LiC₆ as well as previously undetected gas like GIC stages (precursors).

A real‐time quantification of Li transport using a nondestructive neutron method to measure the Li distribution upon charge and discharge in a Li‐ion cell is reported. By using in situ neutron depth profiling (NDP), we probed the onset of lithiation in a high‐capacity Sn anode and visualized the enrichment of Li atoms on the surface followed by their propagation into the bulk. The delithiation process shows the removal of Li near the surface, which leads to a decreased coulombic efficiency, likely because of trapped Li within the intermetallic material. The developed in situ NDP provides exceptional sensitivity in the temporal and spatial measurement of Li transport within the battery material. This diagnostic tool opens up possibilities to understand rates of Li transport and their distribution to guide materials development for efficient storage mechanisms. Our observations provide important mechanistic insights for the design of advanced battery materials.

The use of a reference electrode (RE) is necessary to independently measure the overpotential of each electrode in solid oxide fuel cells (SOFC). This type of set‐up, known as the 3‐electrode (or 3‐terminal) configuration, can give erroneous results if the RE does not effectively separate the potential of the two active electrodes. In this work, calculations and experiments were performed to verify the effectiveness of the 3‐electrode configuration used in electrochemical impedance spectroscopy (EIS) measurements for studying the kinetics of anodes and cathodes in SOFC. Initially, a theoretical analysis of the impedance distortions in relation to the electrode geometry and configuration is presented and the main causes of distortions are elucidated. Then, this analysis is corroborated by experimental results obtained using two specially designed cells. Calculations and experiments reconfirm that configurations characterised by electrodes of equal area and symmetrical placement do not produce EIS distortions when the electrodes have similar area‐specific polarisation resistances and time constants. Moreover, distortions can be low even in considerably misaligned configurations when electrodes are small and relatively inactive.