Abstract
Electrochemical CO
2
reduction reaction (CO
2
RR) to liquid fuels is currently challenged by low product concentrations, as well as their mixture with traditional liquid electrolytes, such ...as KHCO
3
solution. Here we report an all-solid-state electrochemical CO
2
RR system for continuous generation of high-purity and high-concentration formic acid vapors and solutions. The cathode and anode were separated by a porous solid electrolyte (PSE) layer, where electrochemically generated formate and proton were recombined to form molecular formic acid. The generated formic acid can be efficiently removed in the form of vapors via inert gas stream flowing through the PSE layer. Coupling with a high activity (formate partial current densities ~450 mA cm
−2
), selectivity (maximal Faradaic efficiency ~97%), and stability (100 hours) grain boundary-enriched bismuth catalyst, we demonstrated ultra-high concentrations of pure formic acid solutions (up to nearly 100 wt.%) condensed from generated vapors via flexible tuning of the carrier gas stream.
Electrochemical reduction of carbon dioxide (CO2) to fuels and chemicals provides a promising solution for renewable energy storage and utilization. Among the many possible reaction pathways, CO2 ...conversion to carbon monoxide (CO) is the first step in the synthesis of more complex carbon‐based fuels and feedstocks, and holds great significance for the chemical industry. Herein, recent advances in heterogeneous catalysts for selective CO evolution from electrochemical reduction of CO2 are described. With Au catalysts as a paradigm, principles for catalyst design including size, morphology, and grain boundary densities tuning, surface modifications, as well as metal‐support interaction are comprehensively summarized, which shed light on the development of other transition metal catalysts targeting efficient CO2‐to‐CO conversion. In addition, recently emerged novel materials including transition metal single‐atom catalysts, which present significantly different catalytic behaviors compared to their bulk counterparts and thus open up many unexpected opportunities, are summarized. Furthermore, the technical aspects with respect to large‐scale production of CO are presented, focusing on the full‐cell design and implementation. Finally, short comments related to the future direction of real‐word CO2 electrolysis for CO supply are provided in terms of catalyst optimization and technical breakthrough.
Electrocatalytic CO2 reduction, powered by renewable energy sources, has provided a promising route for delocalized energy storage, chemical production applications, and more importantly, closing the carbon loop. The progress of CO2 electroreduction to CO is reviewed by introducing the recent advances in heterogeneous catalysts and the technical breakthroughs in large‐scale production of CO.
Precise electrochemical synthesis under ambient conditions has provided emerging opportunities for renewable energy utilization. Among many promising systems, the production of hydrogen peroxide ...(H2O2) from the cathodic oxygen reduction reaction (ORR) has attracted considerable interest in past decades due to the increasing market demands and the vital role of ORR in the electrocatalysis field. This work describes recent advances in cathodic materials for H2O2 synthesis from 2e- ORR. By using Pt as a stereotype, the tuning knobs are overviewed, including the intrinsic binding strength of oxygenated species, the intermediate diffusion path and the isolation of Pt–Pt ensembles that enable 2e- ORR pathway from 4e- total reduction. This knowledge is successfully applied to other transition metal systems and leads to the discovery of more efficient alloy catalysts with balanced improvement on both activity and selectivity. In addition, mesostructure engineering and heteroatoms doping strategies on carbon‐based materials, which significantly boost the H2O2 production efficiency as compared to intact carbon sites, are also reviewed. Finally, future directions and challenges of transferring developed catalysts from lab scale tests to pilot plant operations are briefly outlooked.
Electrocatalytic oxygen reduction into hydrogen peroxide, powered by renewable energy sources with green inputs of air and water, is a promising route for decentralized H2O2 generation and its onsite application. A focus review of designing principles and recent progress on cathodic materials for enhanced O2 reduction to H2O2 is provided.
The oxygen-evolution reaction (OER) is a key process in water-splitting systems, fuel cells, and metal–air batteries, but the development of highly active and robust OER catalyst by simple methods is ...a great challenge. Here, we report an in situ dynamic surface self-reconstruction that can dramatically improve the catalytic activity of electrocatalysts. A fluoride (F–)-incorporating NiFe hydroxide (NiFe-OH-F) nanosheet array was initially grown on Ni foam by a one-step hydrothermal method, which requires a 243 mV over-potential (η) to achieve a 10 mA cm–2 current density with a Tafel slope of 42.9 mV dec–1 in alkaline media. After the surface self-reconstruction induced by fluoride leaching under OER conditions, the surface of NiFe-OH-F was converted into highly mesoporous and amorphous NiFe oxide hierarchical structure, and the OER activity at η = 220 mV increases over 58-fold. The corresponding η at 10 mA cm–2 decreases to 176 mV with an extreme low Tafel slope of 22.6 mV dec–1; this performance is superior to that of the state-of-the-art OER electrocatalysts.
Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary ...alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h
mg
(0.46 mmol h
cm
). Our Fe single atom catalyst can effectively prevent the N-N coupling step required for N
due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites.
Abstract Oxygen reduction reaction towards hydrogen peroxide (H 2 O 2 ) provides a green alternative route for H 2 O 2 production, but it lacks efficient catalysts to achieve high selectivity and ...activity simultaneously under industrial-relevant production rates. Here we report a boron-doped carbon (B-C) catalyst which can overcome this activity-selectivity dilemma. Compared to the state-of-the-art oxidized carbon catalyst, B-C catalyst presents enhanced activity (saving more than 210 mV overpotential) under industrial-relevant currents (up to 300 mA cm −2 ) while maintaining high H 2 O 2 selectivity (85–90%). Density-functional theory calculations reveal that the boron dopant site is responsible for high H 2 O 2 activity and selectivity due to low thermodynamic and kinetic barriers. Employed in our porous solid electrolyte reactor, the B-C catalyst demonstrates a direct and continuous generation of pure H 2 O 2 solutions with high selectivity (up to 95%) and high H 2 O 2 partial currents (up to ~400 mA cm −2 ), illustrating the catalyst’s great potential for practical applications in the future.
The development of advanced catalysts for efficient electrochemical energy conversion technologies to alleviate the reliance on fossil fuels has attracted considerable interest in the last decades. ...Insight into the roles of reactive sites in nanomaterials is significant for understanding and implementing the design principles of nanocatalysts. Recently, the essential role of defects, including vacancies, reconstructed defects, and doped non-metal (or metal)-defect-based motifs, have been widely demonstrated to promote the diverse electrochemical processes (e.g., O2 or CO2 reduction reactions and H2 or O2 evolution reactions). Nevertheless, the in-depth exploration of the underlying defect electrocatalytic mechanism is still in its infancy. This review summarizes the state-of-the-art defect engineering strategies for designing highly efficient electrochemical nanocatalysts with special emphasis on the correlation between defect structures and electrocatalytic properties. Finally, some perspectives on the challenges and future research directions in this promising area are presented.
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Electrocatalytic energy conversion technologies have been widely considered a clean and sustainable way to alleviate the reliance on fossil fuels. The development of efficient and affordable electrocatalysts plays a key aspect in energy conversion processes by lowering the reaction kinetic barriers and thus boosting the efficiency and selectivity of diverse electrochemical reactions (e.g., oxygen and hydrogen evolution reactions and oxygen and carbon dioxide reduction reactions). Recently, defect engineering has emerged as a new strategy for tailoring the electronic structures and interface coordination; however, the role of “defect”-related sites in as-designed electrocatalysts has not yet been fully understood. In this review, we will shed light on the recent advances in tailoring nanomaterials from the aspects of constructing defect-based motifs as active sites for versatile electrochemical energy conversions as well as their underlying mechanism on structure-property correlations.
Recently, the essential role of defects, including vacancies, reconstructed defects, and doped non-metal/metal-defect-based motifs, has been widely demonstrated to promote the diverse electrochemical processes (e.g., O2/CO2 reduction reactions and H2/O2 evolution reactions). This review summarizes the state-of-the-art defect engineering strategies for designing highly efficient electrochemical nanocatalysts with special emphasis on the correlation between defect structures and electrocatalytic properties. Finally, some perspectives on the challenges and future research directions in this promising area are presented.
The electrochemical synthesis of chemicals and fuel feedstocks has been demonstrated to be a sustainable and “green” alternative to traditional chemical engineering, where oxygen evolution reaction ...(OER) plays a vital role in coupling with various cathodic reactions. While tremendous attention, involving both research and review topics, has been focused on pushing the limit of OER catalysts’ activity, the long-term stability of OER catalysts, which may play an even more important role in large-scale electrolysis industrialization, has been much less emphasized. Until this point, few systematic strategies for developing OER catalysts with industrially relevant durability have been reported. In this review, critical mechanisms that could influence OER stability are summarized, including surface reconstruction, lattice oxygen evolution, and the dissolution-redeposition process of catalysts. Moreover, to bridge the gap between lab-scale OER tests and large-scale electrocatalysis applications, stability considerations in electrolyzer design for long-term operation are also discussed in detail. This review provides catalyst and reactor design principles for overcoming OER stability challenges and will focus more attention from the field on the great importance of OER stability as well as future large-scale electrocatalysis applications.
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Recently, clean energy conversion through electrocatalysis is evolving rapidly as a promising alternative to fossil-fuel energy systems. However, electrolyzers have always suffered from long-term stability challenges, especially for the anodic oxygen evolution reaction catalysts. So far, other than high-cost noble-metal catalysts such as IrO2, no catalysts with industrially relevant stability for oxygen evolution process in acidic and neutral conditions have been demonstrated. Thus, mechanisms that lead to catalytic instability require further investigation and deep understanding to guide future catalyst design.
In order to explore both the origins of and solutions to the stability challenges, this review provides a comprehensive overview and analysis on mechanistic studies of OER catalytic stability. Surface reconstruction of catalysts under oxidation potential during oxygen evolution is one of the causes of catalyst degradation. In addition, lattice oxygen can sometimes participate in the reaction pathway and induce structural instability of catalysts. In addition, redeposition of dissolved ions onto the catalyst surface is a process that gains less attention but can greatly influence the catalytic stability. Besides the catalyst consideration, critical elements of electrolyzers are also discussed in this review to provide insights in electrolysis operation under more realistic conditions. Based on the studies summarized in this article, we also provide potential strategies to design stable OER catalysts. By appropriately tuning the components, structures, dissolution, and redeposition rates of catalysts, we believe that the development of catalysts with long-term stability for oxygen evolution reaction can be achieved in the near future.
Oxygen evolution reaction (OER) plays a vital role in clean energy conversion through electrochemical synthesis of chemicals and fuel feedstocks. However, OER catalysts have always suffered from long-term stability challenges. This review timely summarizes critical reaction mechanisms that could influence OER stability, discusses stability considerations for reactor designs, and proposes future perspectives and potential strategies for designing stable OER catalysts to overcome these challenges.
Electrochemical oxygen reduction to hydrogen peroxide (H
O
) 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
O
selectivity (over 80%) under industrial-relevant generation rates (over 400 mA cm
) 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
O
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
O
via implementing this cation effect for practical applications.
Two-dimensional layered materials like MoS2 have shown promise for nanoelectronics and energy storage, both as monolayers and as bulk van der Waals crystals with tunable properties. Here we present a ...platform to tune the physical and chemical properties of nanoscale MoS2 by electrochemically inserting a foreign species (Li+ ions) into their interlayer spacing. We discover substantial enhancement of light transmission (up to 90% in 4 nm thick lithiated MoS2) and electrical conductivity (more than 200×) in ultrathin (∼2–50 nm) MoS2 nanosheets after Li intercalation due to changes in band structure that reduce absorption upon intercalation and the injection of large amounts of free carriers. We also capture the first in situ optical observations of Li intercalation in MoS2 nanosheets, shedding light on the dynamics of the intercalation process and the associated spatial inhomogeneity and cycling-induced structural defects.
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