bluuebunny/crossref_metadata_2025_split huggingface dataset:
Understanding Water Dissociation Physics through Controlled Oxide Surface Chemistry
Authors: Stovall Timothy Nathan , Bui Justin C. , Boettcher Shannon W. , Weber Adam Z. 
Published: December 2024

Bipolar membranes (BPMs) provide a platform for the interconversion between electric and chemical potential gradients and the precise control over local ion concentrations and fluxes, making BPMs attractive materials for many electrochemical processes. In reverse bias charge carriers must be generated via heterolytic water dissociation (WD, 2H2O → OH- + H3O+), and which must be accomplished at high rates and low overpotentials to realize scalable BPM applications. It is hypothesized that WD is driven by a combination of electric field and catalytic effects within the bipolar junction. However, the extent to which each contributes to observed rates, and the possible interplay between the two, is yet to be resolved.
Here, we explore the interfacial physics within the BPM to understand the kinetics and mechanisms of water dissociation on TiO2 and graphene oxide (GO) derivative catalysts. Using a membrane-potential-sensing testbed we isolate the WD polarization signature in a BPM water electrolyzer. We find that neat-GO exhibits an anomalous exponential current response as a function of WD overpotential, contrary to the linear polarization response of TiO2 (and other metal oxides, reported previously). Similarly, the rates were independent of GO loading, contrasting the typical U-shaped loading dependence on WD performance using metal oxide catalysts. We hypothesize the unique behavior of GO can be linked to the double layer profile within the bipolar junction, which can be screened and localized to the catalyst/AEL interface via the acidic carboxylate moieties on the GO surface. We validate this framework by controlling the degree of hydroxyl/carboxylation on the graphene-oxide surface, and thus the electric double layer profile, to control the polarization response. Using temperature-dependent measurements at varying potentials and a simple Arrhenius-type equation we decouple the apparent enthalpic and entropic driving forces for WD within a confined and polarized heterojunction. Broadly, this work advances our understanding of the interplay between catalyst surface chemistry and electric double layer formation under confinement, and how this effect can be leveraged in (electro)chemical transformations.

Figure 1. A large electric field within the catalyst layer increases the WD rate within the BPM

Figure 1
Cation Effect on the Product Selectivity of Electrochemical CO Reduction
Authors: Ni Weiyan , Liang Yongxiang , Cao Yufei , Chen Zhu , Sargent Edward H. 
Published: December 2024

Renewable electricity-powered reduction of CO2 (CO2R) is a promising route to upgrade CO2 to ethylene, an industrial feedstock in high demand. Compared with direct CO2 electroreduction to ethylene, CO2-CO-C2H4 tandem electrolysis is more carbon efficient, circumventing CO2 crossover and carbonate formation. However, current CO electroreduction produces a mixture of multi-carbon products (ethylene, ethanol, acetate, and propanol), and the mechanism underlying this dispersion of selectivity remains unclear.
We studied the role of the microenvironment of the electrode in selectivity among C2+ products, and hypothesized that destabilizing the oxygen-containing intermediates would direct the reaction pathway toward the sole oxygen-free C2+ product, ethylene. When we explore the cations in electrolyte, we find the one with the most robust hydration shell (Li) promotes ethylene production, among C2+ products, compared to weakly hydrated cations (e.g. K). This is a distinctive trend compared to studies of activity that found reverse cation trend in jc2+. A combined study of operando Raman spectroscopy, MD simulation, and DFT calculation suggests that the strongly hydrated Li+ on the electrode surface has the greatest H2O-Ointermediate interaction and the least cation-Ointermediate interaction. This increases the difference in activation energy of the selectivity-determining step between ethylene pathway and oxygenates pathway, and hence leads to the preference of Li for hydrocarbons over oxygenates.

Figure 1
Mechanistic Insights into the Electrochemical Oxidation of 5-Hydroxymethylfurfural on a Thin Film Ni Anode
Authors: Prajapati Aditya , Govindarajan Nitish , Sun Wenyu , Jeong Huiyun , Feaster Jeremy , Akhade Sneha A , Bucci Giovanna , Hahn Christopher 
Published: December 2024

Oxygen evolution reaction (OER) in ambient electrolyzers consumes a significant amount of energy and yields oxygen, an inherently low-value product. Therefore, it is imperative to choose anodic reactions that can make efficient use of the supplied energy to the electrolyzer when paired with a desired cathodic reaction such as CO2 reduction into value-added commodities. Utilizing biomass oxidation offers a promising avenue to reduce the overall energy input by >50% while producing high-value chemicals, and address the critical requirements for biomass conversion, a crucial 21st-century non-fossil carbon resource. In this work, we demonstrate the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) as an alternative to OER. This reaction not only reduces the theoretical overall energy input into the electrolyzer but also generates FDCA, a significant building block for the sustainable polyester PEF, which has a global market size of more than 30 Mt/yr. We present an experimental and computational approach to understand HMF oxidation on Ni-based catalysts. Our experimental investigation involves evaluating the effect of microenvironment on thin-film (5nm) Ni-catalyst in a pH range of 11-13 to understand the intrinsic kinetics of HMF oxidation. In addition, we compare the reaction energetics of OER and the hydride transfer reaction of the HMF oxidation using density functional theory to understand the competing reaction pathways on the anode. Using the experimental data, we also develop a Multiphysics model to evaluate the electrode kinetics and species concentration distribution near the catalyst surface to understand the implications of mass transport limitations in this electrochemical system. This comprehensive analysis could potentially provide new guidelines to design more energy-efficient anodes for upgrading sustainable alcohols.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
(Keynote) Copper Cathode for Electrochemical CO2 Reduction – Unanswered Questions on Reproducibility
Authors: Marshall Aaron Timothy , Heenan Alex Reynell , Tiffin Campbell Maurice 
Published: December 2024

Electrocatalytic reduction of CO2 has the potential to convert CO2 into carbon-based fuels by using renewable energy. For many years, copper based cathodes have been highlighted as the quintessential electrocatalytic surface for CO2 reduction (exemplified by the work of Hori). While gas-diffusion electrodes have shown than industrially relevant reaction rates can be achieved using relatively simple cathode materials, there are still many unanswered questions regarding the behaviour of copper cathodes in aqueous solutions. In particular, a review of the literature reveals that a very wide range of product selectivities are found at seemingly similar conditions (Figure 1). Rather surprisingly this review shows that sometimes copper can have almost no activity for CO2 reduction and instead evolve almost pure H2. Our own measurements confirm this unexpected behaviour, with replicate experiments revealing occasions where identically mechanically polished copper electrodes favour hydrogen evolution over CO2 reduction. In this presentation, we will discuss the reproducibility of CO2 reduction and the steps taken to explain copper’s highly variable product selectivity.
Figure 1: Results from literature for faradaic efficiency of common CO2 reduction reaction products on polycrystalline copper (black lines) and other forms of copper (red lines) at -1 (± 0.1) V vs RHE in CO2 saturated 0.1 M KHCO3.

Figure 1
Temperature Effects on the Surface Dynamics of the CO2 Reduction Reaction over Copper
Authors: Brandão Victor D. , Long Oliver , Song Hakhyeon , Venkatamaran Anush , Nair Sankar , Hatzell Marta C. , Sievers Carsten , Bhargava Saket , Arora Sukaran , Villa Carlos 
Published: December 2024

The electrochemical reduction of CO2 (CO2RR) has stood out as a pathway to mitigate carbon emissions and supply multi-carbon feedstocks to the chemical industry. While most CO2RR studies over copper are carried out at room temperature, heat transfer limitations in the electrolyte will result in temperature buildup near the electrode in industrial CO2 electrolyzers. Reaction temperature plays a key role in the reaction activity and product selectivity by controlling the distribution of species on the copper surface. In this study, we use surface enhanced infrared absorption spectroscopy (SEIRAS) and surface enhanced Raman spectroscopy (SERS) to investigate the effect of temperature on the dynamics of reactive intermediates in the reaction microenvironment (Fig. A).
Using SEIRAS, we showed site-specific CO coverage is dependent on temperature, and how CO migration seems to directly impact product distribution at higher temperatures. We found that increasing temperature leads to decreased CO and increased alkyl groups coverage for a given potential (Fig. B). This suggests that temperature has a direct effect on the selection of mechanistic pathways in the conversion of CO to C1 and C2 products, beyond just controlling mass transport and local CO2 availability. Using SERS, we showed that the local pH is considerably higher than their bulk values, and that higher temperatures consistently led to higher local pH values (Fig. C). The significant depletion of local hydrogen with increasing temperature indicates that local pH plays a key role in driving reaction selectivity dependence on temperature. Understanding the effect of temperature on the CO2RR surface dynamics through surface sensitive techniques is a key step to rationalize product distribution and to design solutions for enhanced C2+ production in industrial CO2 electrolyzers.

Figure 1
Ion Implantation of Copper Electrodes to Elucidate the Effect of Subsurface Oxygen and Surface Roughness for the Electrochemical CO2 Reduction Reaction
Authors: Heenan Alex Reynell , Fang Vivian , Kennedy John , Marshall Aaron Timothy 
Published: December 2024

The electrochemical reduction of CO2 has the potential to be a viable method to consume anthropogenic CO2, while producing value added products such as CO and C2H4 in a carbon negative way. Copper is a unique electrocatalyst for the CO2 reduction reaction as it can produce products that require more than two electrons (such as C2H4 and C2H5OH) with reasonable selectivity. This has resulted in copper being an intensely studied catalyst over the past several decades in an attempt to understand why it is able to produce these unique products, but also to promote the production of the likes of C2H4 and C2H5OH with better selectivity, activity and stability. While excellent progress has been made, there is still plenty of debate around whether the enhanced performance of copper electrodes stems from surface roughness effects or subsurface oxygen.
In the past, these two mechanisms have been difficult to decouple because of the fact that to synthesise an electrode with subsurface oxygen, surface roughness also tends to be induced. In this work, ion implantation of neon and oxygen was used to decouple these effects. The theory was that while the oxygen ion implantation will induce subsurface oxygen sites and surface roughness, the neon ion implantation will only induce surface roughness. Interestingly, it was found that both the oxygen and neon ion implantation resulted in decreased activity and selectivity for CO and C2+, with increasing ion fluence. These decreases in performance were in spite of an increase in the surface roughness of the electrode, which means that the ion implantation affected the inherent performance of the catalyst. This was in contrast to the sample that was annealed in air which had increased surface roughness, however, the normalised activity was consistent with that of the as-made catalyst. X-ray absorption spectroscopy and x-ray photoelectron spectroscopy were used to understand the loss in performance, which showed that the as the ion fluence increased, the Cu:CuO ratio and the relative O 1s Cu2O concentration on the electrode surface increased in an equivalent fashion for both the neon and oxygen implantation. Additionally, there was also a decrease in the number of oxygen vacancies, with increasing ion fluence. This shows that while the ion implantation increased the surfaced roughness of the electrode, it was able to reduce the surface Cu2+ to Cu1+ and Cu0, which resulted in the decreased performance of the electrode, suggesting that the subsurface oxygen is the key parameter that should be optimised, over the surface roughness of the electrode.
(Invited) Reconstruction of Metal-Organic Framework-Based Heterogeneous Catalysts during CO2 Electroreduction
Authors: Nam Dae-Hyun 
Published: December 2024

Electrochemical CO2 reduction reaction (CO2RR), which enables CO2 conversion into value-added fuels and chemical feedstocks, provides an avenue toward carbon neutrality and renewable energy storage. In the CO2RR, heterogeneous electrocatalysts are essential to activate substrate species and interact with reaction intermediates for efficient and selective CO2 conversion. Especially, Cu-based active sites in the catalysts enable C-C coupling via *CO dimerization for multi-carbon (C2+) chemicals production. Although judiciously controlled surface of catalysts is required to control the binding of CO2RR intermediates, the active sites of the catalysts undergo severe reconstruction during electrochemical reaction. This hinders the identification of active sites because it induces structure and phase evolution of electrocatalysts during CO2RR. Therefore, reconstruction is a major bottleneck in the development of CO2RR, and it has remained as a challenge to unveil the mechanism of reconstruction.
Here, I will present our recent efforts to understand the reconstruction of Cu-based metal-organic framework (MOF) during electrochemical CO2RR. MOFs have porous structures where the organic linkers are bonded with metal node in secondary building unit (SBU). We verified that oxidation tendency of metal ions in SBU is a key to determine the stability of MOFs. Pourbaix diagram helps to predict the trend of metal reduction in MOFs during CO2RR. Operando X-ray absorption spectroscopy (XAS) during CO2RR enabled to track the states of metal node in MOFs. We found that Cu ions in Cu-MOFs can be reduced to pure Cu states during CO2RR. This reveals the reconstruction of Cu-MOFs under reductive potential. To unveil the reconstruction behaviors of Cu active sites in the MOFs, we investigated the CO2RR of Cu benzene-1,3,5-tricarboxylate (Cu-BTC) and Cu benzene-1,4-dicarboxylate (Cu-BDC) MOFs. Unlike the Cu-BTC which resulted in the formation of C1 chemicals as major products, Cu-BDC produced C2 chemicals such as ethylene (C2H4) in CO2RR. We elucidate how the catalytic active sites of Cu-MOFs undergo the reconstruction and evolve during CO2RR. Also, we explain the how the reconstruction of Cu active sites in MOFs affects the steering of CO2RR pathway. In the concluding remarks, the future perspective in the catalyst reconstruction during CO2RR will be discussed.
Effect of Cathodic Potential in Electrochemical CO2 Reduction
Authors: Wang Lei 
Published: December 2024

In this presentation, we will discuss the critical role of cathodic-potential in modulating the selectivity, activity and even stability of electroreduction of CO2 (CO2R). We will first introduce the potential-dependent selectivity in Cu-based CO(2)R, originating from a combination of pH-effect, kinetics of different *CO activation pathways, local field effect, and CO coverage effects, etc. By carefully elucidating the intricate interplays among these effects, we could leverage cathodic potential as an effective lever to steer the CO(2)R selectivity towards multi-carbon-products. Additionally, we will introduce how cathodic-potential plays affects the CO2R stability, particularly in preventing the electrolyte flooding. Specifically, we observed that CO2R kinetic-curves typically enter the mixed-control-region at approximately > 0.75 V, and then quickly transition to the CO2 mass transport-limited-region, regardless of the type of GDE used or the current density achieved. This suggests that GDE flooding is closely associated with the cathodic-potential. Inspired by this understanding, we demonstrate that an intrinsically more active catalyst capable of sustaining a sufficient CO2R current at a low cathodic potential before entering the mixed-controlled region can lead to significantly enhanced CO2R stability and improved energy efficiency.
If time allows, we will also briefly introduce two non-Cu-based systems:
(1) The potential-dependent structural-evolution of Pd-based catalysts during CO2R to formate. We found that by manipulating the valence state of Pd, one could substantially extend the cathodic-potential window for stabilizing the desired a-Pd phase, achieving robust and efficient CO2-to-formate conversion on Pd-catalysts.
(2) The potential-dependent CO2-to-methanol production on Co-Phthalocyanine. Here, the cathodic-potential is critical in inducing the structural-distortion of the Co-N4 plane, influencing the *CO binding mode and strength, which leads to the selectivity change from CO to methanol on Co-Phthalocyanine.
Overall, we wish to underscore the importance of considering cathodic potential as a crucial parameter in the design and optimization of electrochemical CO2R systems.
Activating New Reaction Pathways in Electrochemical CO2 Conversion Using Pulsing
Authors: Mayer Matthew T. , Arndt Alexander , Pardo Perez Laura Carolina , Ma Chaoqun , Bogdanoff Peter 
Published: December 2024

Electrochemical CO2 conversion can result in a variety of products, often as a mixture, and controlling the product selectivity remains a key challenge. It has been shown that pulsing the electrochemical potential can lead to altered product distributions, influenced by effects on, e.g., transport, double-layer rearrangement, adsorption/desorption, and changes to electrode structure and composition (1).
Herein we report our observations using metal electrodes normally selective for the 2-electron formation of CO as major product under steady-state (potentiostatic) conditions, finding that they can produce significant amounts of higher-order products (including methane and ethylene) under the application of pulse potential waveforms. We confirm this is not due to metal impurities in the system, but is significantly affected by phenomena such as surface restructuring and accumulation of liquid products. Furthermore, time-resolved differential electrochemical mass spectrometry (DEMS) measurements reveal distinctly different transient behaviors between the different gaseous products, providing key new mechanistic insight for clarifying the roles of pulsing.
(1) Casebolt, R.; Levine, K.; Suntivich, J.; Hanrath, T. Pulse Check: Potential Opportunities in Pulsed Electrochemical CO2 Reduction. Joule
2021, 5 (8), 1987–2026. https://doi.org/10.1016/j.joule.2021.05.014.

Figure: Pulsed CO2 reduction on Ag (manuscript pending) -- a) Pulsing waveform with parameter definitions. b) Gas product evolution rates as measured by GC during continuous electrochemical pulsing of a silver foil electrode. c) DEMS study of porous Ag film electrodes, revealing product formation transient behaviors. d) Selectivity dependence on varying the cathodic step potential (Ec) while Ea is fixed.

Figure 1
Atomically Dispersed Ni-N-C Catalysts for Electrochemical Carbon Dioxide Reduction
Authors: Ko Youngdon , Osmieri Luigi , Zhang Hanguang , Zelenay Piotr 
Published: December 2024

Electrochemical carbon dioxide reduction reaction (CO2RR) has the potential to play a key role in addressing major energy and environmental challenges via clean conversion of the atmospheric CO2 from combusting of fossil fuels into value-added products such as fuels and chemicals. The products generated by CO2RR vary depending on the electrocatalyst used at the CO2 electrolyzer cathode,1 which calls for the development of more active, stable, and selective CO2RR electrocatalysts. Atomically dispersed Ni-N-C catalysts have attracted attention due to their superior selectivity for CO generation.2 Their activity and selectivity towards CO2RR are influenced by the metal center and its local coordination environment in Ni-N-C catalysts.3 Ni-N-C catalysts derived from zeolitic imidazolate frameworks (ZIFs) have multiple advantages including a high specific surface area, customizable pore structures, and controllable morphologies, even after the carbonization treatment at high temperatures.
In this presentation, we will focus on ZIF-derived Ni-N-C catalysts using a ligand exchange strategy during ZIF synthesis. These ligand-exchanged ZIFs are synthesized by partially replacing 2-methylimidazole (used in ZIF-8 synthesis) with different imidazole-like ligands for the purpose of obtaining structures with increased porosity. The effects of several parameters, including ligand exchange percentage and pyrolysis temperature for synthesizing Ni-N-C catalysts will be evaluated. We will show how the physicochemical characteristics of the Ni-N-C catalyst, i.e., porosity, hydrophobicity, and density of active sites, can be tuned by varying the synthesis parameters. We will focus in particular on the optimization of porosity and accessibility of CO2 to the catalyst’ active sites to maximize CO2RR rate.

Acknowledgement

Research presented in this work has been supported by the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory under project number 20230065DR.

References

(1) Varela, A. S.; Ju, W.; Bagger, A.; Franco, P.; Rossmeisl, J.; Strasser, P. Electrochemical Reduction of CO2 on Metal-Nitrogen-Doped Carbon Catalysts. ACS Catalysis
2019, 9 (8), 7270-7284.
(2) Ju, W.; Bagger, A.; Hao, G.-P.; Varela, A. S.; Sinev, I.; Bon, V.; Roldan Cuenya, B.; Kaskel, S.; Rossmeisl, J.; Strasser, P. Understanding activity and selectivity of metal-nitrogen-doped carbon catalysts for electrochemical reduction of CO2. Nature Communications
2017, 8 (1), 944.
(3) Liang, S.; Huang, L.; Gao, Y.; Wang, Q.; Liu, B. Electrochemical Reduction of CO2 to CO over Transition Metal/N-Doped Carbon Catalysts: The Active Sites and Reaction Mechanism. Advanced Science
2021, 8 (24), 2102886.