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18 result(s) for "García-Melchor, Max"
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Enabling heterogeneous catalysis to achieve carbon neutrality: Directional catalytic conversion of CO2 into carboxylic acids
The increase in anthropogenic carbon dioxide (CO2) emissions has exacerbated the deterioration of the global environment, which should be controlled to achieve carbon neutrality. Central to the core goal of achieving carbon neutrality is the utilization of CO2 under economic and sustainable conditions. Recently, the strong need for carbon neutrality has led to a proliferation of studies on the direct conversion of CO2 into carboxylic acids, which can effectively alleviate CO2 emissions and create high‐value chemicals. The purpose of this review is to present the application prospects of carboxylic acids and the basic principles of CO2 conversion into carboxylic acids through photo‐, electric‐, and thermal catalysis. Special attention is focused on the regulation strategy of the activity of abundant catalysts at the molecular level, inspiring the preparation of high‐performance catalysts. In addition, theoretical calculations, advanced technologies, and numerous typical examples are introduced to elaborate on the corresponding process and influencing factors of catalytic activity. Finally, challenges and prospects are provided for the future development of this field. It is hoped that this review will contribute to a deeper understanding of the conversion of CO2 into carboxylic acids and inspire more innovative breakthroughs. This review summarizes the application prospects of carboxylic acids and the basic principles of carbon dioxide (CO2) conversion into carboxylic acids through photo‐, electric‐, and thermal catalysis. The current understanding of the mechanistic process for converting CO2 into carboxylic acids and the preparation of high‐performance catalysts have been well elaborated. Moreover, challenges and prospects are provided for the future development of this field.
Electrochemical CO2 Reduction: Commercial Innovations and Prospects
Sustainability is an imperative requirement in this era, with electrocatalytic power into fuels technologies emerging as a significant route toward sustainable chemistry. One of the focus areas within the chemical industry is capture of carbon dioxide (CO2) and its electrochemical reduction (eCO2RR) into economically viable commodities through the utilization of renewable sources. Despite some specific eCO2RR technologies being poised for market introduction, the development of a comprehensive technology for eCO2RR remains a challenge. While certain technologies targeting specific eCO2RR products are on the verge of deployment, substantial efforts are still necessary to transition and establish presence in the market over conventional technologies. This review highlights recent technological advancements, fundamental studies, and the persisting challenges from an industrial perspective. We take a deep dive into the research methodologies, strategies, challenges, and advancements in the development of applications for eCO2RR. Specifically, three eCO2RR products – CO, HCOOH, and C2H4 – as promising candidates for implementation are elaborated based on techno‐economic considerations. Additionally, the review discusses the industrial blueprint for these products, aiming to streamline their path toward commercialization. The intent is to present the status of eCO2RR, offering insights into its potential transformation from a mere laboratory curiosity to a feasible technology for industrial chemical synthesis. This review highlights recent technological advancements and the persisting challenges from an industrial perspective in building the significant ecosystem for development of eCO2RR technology to products. The roadblocks due to lack of collaboration in areas such as catalyst development, basic electrochemical analysis, computational modelling, engineering, and economic feasibility of the value chain are discussed.
Applying Active Learning to the Screening of Molecular Oxygen Evolution Catalysts
The oxygen evolution reaction (OER) can enable green hydrogen production; however, the state-of-the-art catalysts for this reaction are composed of prohibitively expensive materials. In addition, cheap catalysts have associated overpotentials that render the reaction inefficient. This impels the search to discover novel catalysts for this reaction computationally. In this communication, we present machine learning algorithms to enhance the hypothetical screening of molecular OER catalysts. By predicting calculated binding energies using Gaussian process regression (GPR) models and applying active learning schemes, we provide evidence that our algorithm can improve computational efficiency by guiding simulations towards candidates with promising OER descriptor values. Furthermore, we derive an acquisition function that, when maximized, can identify catalysts that can exhibit theoretical overpotentials that circumvent the constraints imposed by linear scaling relations by attempting to enforce a specific mechanism. Finally, we provide a brief perspective on the appropriate sets of molecules to consider when screening complexes that could be stable and active for this reaction.
Gold-supported cerium-doped NiOx catalysts for water oxidation
The development of high-performance catalysts for the oxygen-evolution reaction (OER) is paramount for cost-effective conversion of renewable electricity to fuels and chemicals. Here we report the significant enhancement of the OER activity of electrodeposited NiO x films resulting from the combined effects of using cerium as a dopant and gold as a metal support. This NiCeO x –Au catalyst delivers high OER activity in alkaline media, and is among the most active OER electrocatalysts yet reported. On the basis of experimental observations and theoretical modelling, we ascribe the activity to a combination of electronic, geometric and support effects, where highly active under-coordinated sites at the oxide support interface are modified by the local chemical binding environment and by doping the host Ni oxide with Ce. The NiCeO x –Au catalyst is further demonstrated in a device context by pairing it with a nickel–molybdenum hydrogen evolution catalyst in a water electrolyser, which delivers 50 mA consistently at 1.5 V over 24 h of continuous operation. Efficient catalysts for the oxygen-evolution reaction, especially in alkaline media, are highly desired because of their application in various energy technologies. Now, a gold-supported NiCeO x catalyst is shown to have excellent catalytic activity due to synergistic geometric and electronic effects.
Faster hydrogen production in alkaline media
Nickel–iron and cobalt–iron (oxy)hydroxides are state-of-the-art electrocatalysts for oxygen production in alkaline conditions. Now, the addition of high-valent dopants has been demonstrated to further propel the catalytic rate in these materials by an order of magnitude.
Universal scaling relations for the rational design of molecular water oxidation catalysts with near-zero overpotential
A major roadblock in realizing large-scale production of hydrogen via electrochemical water splitting is the cost and inefficiency of current catalysts for the oxygen evolution reaction (OER). Computational research has driven important developments in understanding and designing heterogeneous OER catalysts using linear scaling relationships derived from computed binding energies. Herein, we interrogate 17 of the most active molecular OER catalysts, based on different transition metals (Ru, Mn, Fe, Co, Ni, and Cu), and show they obey similar scaling relations to those established for heterogeneous systems. However, we find that the conventional OER descriptor underestimates the activity for very active OER complexes as the standard approach neglects a crucial one-electron oxidation that many molecular catalysts undergo prior to O–O bond formation. Importantly, this additional step allows certain molecular catalysts to circumvent the “overpotential wall”, leading to enhanced performance. With this knowledge, we establish fundamental principles for the design of ideal molecular OER catalysts. While water electrolysis affords hydrogen as a carbon-neutral fuel, the oxygen evolution half-reaction limits overall performances. Here, authors examine molecular catalysts and their water oxidation mechanisms via computational methods.
Homogeneously dispersed multimetal oxygen-evolving catalysts
Earth-abundant first-row (3d) transition metal–based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER.
Equilibrium oxygen storage capacity of ultrathin CeO2-δ depends non-monotonically on large biaxial strain
Elastic strain is being increasingly employed to enhance the catalytic properties of mixed ion–electron conducting oxides. However, its effect on oxygen storage capacity is not well established. Here, we fabricate ultrathin, coherently strained films of CeO 2-δ between 5.6% biaxial compression and 2.1% tension. In situ ambient pressure X-ray photoelectron spectroscopy reveals up to a fourfold enhancement in equilibrium oxygen storage capacity under both compression and tension. This non-monotonic variation with strain departs from the conventional wisdom based on a chemical expansion dominated behaviour. Through depth profiling, film thickness variations and a coupled photoemission–thermodynamic analysis of space-charge effects, we show that the enhanced reducibility is not dominated by interfacial effects. On the basis of ab initio calculations of oxygen vacancy formation incorporating defect interactions and vibrational contributions, we suggest that the non-monotonicity arises from the tetragonal distortion under large biaxial strain. These results may guide the rational engineering of multilayer and core–shell oxide nanomaterials. The surface oxygen storage capacity is an important metric of catalytic activity, but its dependence on strain is not well characterized. Here, the authors show the surface oxygen nonstoichiometry in coherently strained CeO2-δ films increases non-monotonically with biaxial strain.
Two-Dimensional Materials as Catalysts for Energy Conversion
Although large efforts have been dedicated to studying two-dimensional materials for catalysis, a rationalization of the associated trends in their intrinsic activity has so far been elusive. In the present work we employ density functional theory to examine a variety of two-dimensional materials, including, carbon based materials, hexagonal boron nitride ( h -BN), transition metal dichalcogenides (e.g. MoS 2 , MoSe 2 ) and layered oxides, to give an overview of the trends in adsorption energies. By examining key reaction intermediates relevant to the oxygen reduction, and oxygen evolution reactions we find that binding energies largely follow the linear scaling relationships observed for pure metals. This observation is very important as it suggests that the same simplifying assumptions made to correlate descriptors with reaction rates in transition metal catalysts are also valid for the studied two-dimensional materials. By means of these scaling relations, for each reaction we also identify several promising candidates that are predicted to exhibit a comparable activity to the state-of-the-art catalysts. Graphical Abstract Scaling relationship for the chemisorption energies of OH* and OOH* on various 2D materials.
Selective high-temperature CO2 electrolysis enabled by oxidized carbon intermediates
High-temperature CO 2 electrolysers offer exceptionally efficient storage of renewable electricity in the form of CO and other chemical fuels, but conventional electrodes catalyse destructive carbon deposition. Ceria catalysts are known carbon inhibitors for fuel cell (oxidation) reactions; however, for more severe electrolysis (reduction) conditions, catalyst design strategies remain unclear. Here we establish the inhibition mechanism on ceria and show selective CO 2 to CO conversion well beyond the thermodynamic carbon deposition threshold. Operando X-ray photoelectron spectroscopy during CO 2 electrolysis—using thin-film model electrodes consisting of samarium-doped ceria, nickel and/or yttria-stabilized zirconia—together with density functional theory modelling, reveal the crucial role of oxidized carbon intermediates in preventing carbon build-up. Using these insights, we demonstrate stable electrochemical CO 2 reduction with a scaled-up 16 cm 2 ceria-based solid-oxide cell under conditions that rapidly destroy a nickel-based cell, leading to substantially improved device lifetime. CO 2 electrolysers store electricity as CO or other chemical fuels, but can suffer from carbon deposition at the electrodes. Skafte et al. identify a mechanistic route to inhibiting carbon build-up in ceria-based electrolysers and build a cell that operates beyond the thermodynamic carbon deposition threshold.