Search

Understanding the role of defect density in thick oxide passivation layer in electrolyte/oxide/semiconductor (EOS) junction photoanode system is critical for efficient photo-electrochemical water splitting with long-term stability.

The activity and selectivity for C2+ products from electrochemical CO2 reduction in a zero-gap membrane-electrode assembly (MEA) are improved using a synchronous KOH-activation and tailoring of Cu catalyst thickness.

We demonstrate Ni–N/C is an effective electrocatalyst for the direct conversion of captured CO2 in monoethanol amine-based aqueous absorbents showing high CO faradaic efficiency (78%) and its high selectivity is maintained in various amine solvents.

Bimetallic CuPd oxide alloy electrocatalysts can promote selective ammonia production from the nitrate reduction reaction by accelerating the rate-determining hydrogenation of nitrite, which is a critical intermediate.

van der Waals (vdW) heterostructures composed of multiple vertical stacks of two-dimensional materials exhibit unique optoelectronic properties compared with their single constituent counterparts. ...

Pd is one of the most effective catalysts for the electrochemical reduction of CO2 to formate, a valuable liquid product, at low overpotential. However, the intrinsically high CO affinity of Pd makes the surface vulnerable to CO poisoning, resulting in rapid catalyst deactivation during CO2 electroreduction. Herein, we utilize the interaction between metals and metal-organic frameworks to synthesize atomically dispersed Au on tensile-strained Pd nanoparticles showing significantly improved formate production activity, selectivity, and stability with high CO tolerance. We found that the tensile strain stabilizes all reaction intermediates on the Pd surface, whereas the atomically dispersed Au selectively destabilizes CO* without affecting other adsorbates. As a result, the conventional COOH* versus CO* scaling relation is broken, and our catalyst exhibits 26- and 31-fold enhancement in partial current density and mass activity toward electrocatalytic formate production with over 99% faradaic efficiency, compared to Pd/C at -0.25 V versus RHE.

The high capital cost of electrolyzers is one of the major obstacles encountered in the industrial adoption of electrochemical CO2 reduction (CO2R) systems. The anion exchange membrane (AEM) is a major contributor to the cost of electrolyzers. Herein, we propose a strategy for improving the economic feasibility by applying a low-cost porous membrane (PM). For a CO2R reaction (CO2RR), the activity and selectivity of an electrolyzer using a PM were found to be similar to those achieved using an AEM. Furthermore, the physical properties of PM, such as pore size, hydrophobicity, and thickness, can be tuned to suit the CO2RR. A techno-economic analysis of the entire process revealed that adopting a PM is economically advantageous compared to adopting an AEM. Our results not only provide new practical and economical insights into the CO2RR, but also demonstrate its potential extension to a variety of electrolytic systems.

Artificial nitrogen fixation causes excess nitrate (NO3−) production due to an unbalanced nitrogen cycle. Recently, the electrocatalytic nitrate reduction reaction (NO3RR) used to produce value-added chemicals such as ammonia (NH3) has attracted attention as a promising technology for energy and environmental reasons; however, the design of the catalytic material used in this reaction is yet to be fully understood for the production of NH3. Herein, the fundamentals of the NO3RR are introduced to understand the thermodynamics and kinetics of the NO3RR using heterogeneous electrocatalysts, and the analytical methods are explained to provide a precise evaluation of the NO3RR performance. The recent strategies used to design efficient and selective electrocatalysts have been reviewed, including the effects of facets, heterogeneous interfaces, alloying, strain, oxygen vacancies in metal oxides, single atom catalysts, and bio-inspired structures. The critical factors determining the NO3RR activity and selectivity are highlighted in terms of the nitrate adsorption, intermediate nitrite conversion, chemical environment, and intermediate species adsorption upon modifying the electronic and chemical states of the catalyst surface. The NO3RR is potentially applied for the electrochemical synthesis of nitrogen-containing chemicals.

The direct electroconversion of captured CO2 is attracting attention as an alternative to the current energy-demanding CO2 separation processes. In conventional capturing media, the reaction inevitably takes place in the presence of bulky ammonium, leading to steric hindrance and low CO selectivity. Here, for the first time, we present a single atom Ni catalyst (Ni–N/C) exhibits superior activity for the electroconversion of captured CO2, without the need for additives. In a CO2-captured monoethanolamine-based electrolyte, Ni–N/C achieves a notably high CO selectivity of 64.9% at −50 mA cm−2 integrated with a membrane electrode assembly. We also propose that Ni–N/C demonstrates weak cation sensitivity to the CO2 reduction reaction, maintaining high CO production activity in various capturing solutions, while Ag shows a gradual decrease depending on the bulkiness of the amine. These trends provide insights into selective catalyst design for the electroconversion of captured CO2 in universal media.

Atomically dispersed nickel sites complexed on nitrogen-doped carbon (Ni–N/C) have demonstrated considerable activity for the selective electrochemical carbon dioxide reduction reaction (CO2RR) to ...

The demand for non-noble bifunctional electrocatalysts for overall water splitting was increased for simplifying water-splitting systems and accelerating commercialization. Herein, oxygen vacancy-r...

Recent progress in the chemical vapor deposition technique toward growing large-area and single-crystalline two-dimensional (2D) transition metal dichalcogenides (TMDs) has resulted in an electroni...

The conversion of carbon dioxide (CO2) to valuable fuels and chemicals offers a new pathway for sustainable and clean carbon fixation. Recently, the focus has been on electrochemical CO2 reduction on heterogeneous electrode catalysts, leading to remarkable achievements in the reaction performance. To date, CO2 to carbon monoxide (CO) conversion is considered as the most promising candidate reaction for the industrial market, owing to its high efficiency and reasonable technoeconomic feasibility. Moreover, CO has been proposed as a key intermediate species for further reduced hydrocarbons, which can pave the way for various fuel production. This study sets out to describe recent progress on the electrochemical CO2 reduction to CO in a heterogeneously catalyzed system. The review includes understanding of the catalytic material employed and engineering strategies implemented by adjusting the binding energy of key adsorbates. These material design approaches, such as nanostructuring, alloying, doping, and so forth, have pioneered breakouts in the intrinsic catalytic nature of transition metal elements. Moreover, recent advances in systematic design are summarized, with focus on practical industrial applications. Finally, perspectives on the design of electrocatalyst materials for CO production by electrochemical CO2 reduction are presented.

Electrochemical CO2 reduction is always accompanied by a competitive hydrogen evolution reaction as water is used as a hydrogen source. In addition to intrinsic activity control, geometrical factor...

Solar-chemical production is one of the most promising options for producing valuable chemicals from greenhouse gases. An economically attractive and industrially applicable solar-chemical production device not only requires catalyst and/or reactor design, but also auxiliary unit process design, process integration, and optimization. Herein, we report a state-of-the-art monolithic solar-chemical production device having 8.03% solar to CO conversion efficiency and 0.77 to 31.9% CO2 one path conversion. Since the monolithic device directly couples a photovoltaic cell and a CO2 electrolyzer, the power loss due to a current converter can be avoided. According to the solar-chemical production device, a comprehensive process design accounting for CO2 to CO conversion, unreacted CO2 separation, and recycling structure is provided. The process model shows good agreement with experimental data for CO2 conversion in the electrolyzer. A process level techno-economic evaluation and a comprehensive review are also presented to highlight the current state and the economic feasibility of the developed device. Thereafter, we provide a sensitivity analysis in terms of CO2 conversion, membrane cost, solar to chemical efficiency, and current density necessary for economically profitable CO production. The equivalent CO sales cost from a 4 MW production plant is estimated to be $10.9 per kg and the corresponding carbon tax compensating for the price gap of the current market price is $6.6 per kg CO2. The sensitivity analysis demonstrates that >80 mA cm−2 current density or 22% CO2 conversion is desirable to effectively compete with the conventional CO production process.

Electroreduction systems to convert CO2 into CO via Ag electrodes have been intensely studied as a means of producing carbon-neutral fuels or chemical products. However, despite many efforts to maximize the performance of CO-producing systems, the performance of electrochemical cells that produce CO has not yet reached the level of economic viability. Moreover, compared with electrode development attempts, studies on the optimization of large-scale CO-producing systems are lacking, thus impeding the commercialization of electrochemical CO2 reduction systems. In this study, we present optimization results of a pilot-scale CO production system. Operating conditions such as pressure, temperature, and cell voltage were considered as the optimization variables to improve the CO partial current density. To facilitate experiment-based optimization of the pilot-scale operation, we adopted an efficient design of the experiment, for which data points were decided by input–output relations. As a result, the maximum CO partial current reached 2.56 A using a 50 cm2 electrode within 25 experiments. In addition, regression analysis results were provided for future studies on the systematic optimization of electrochemical systems. The operating temperature and CO2 solubility were more highly correlated with the current density and selectivity than was the applied cell voltage, and the CO current density could be predicted with high accuracy.

Cu catalysts prepared by modifying bulk Cu foils have achieved high performance for value-added C2+ compounds from electrochemical CO2 reduction (CO2RR) but the transformation of active sites can be affected by the bulk substrate, which make it complex to design the catalyst. Herein, we newly introduce a simple electrospray pyrolysis method to take advantage of a facile wet-chemical synthesis applicable on non-copper substrates, such as a porous carbon paper, and demonstrate highly enhanced selectivity for C2H4 production from CO2RR. The electrosprayed copper oxide on the carbon paper showed uniquely improved C2 selectivity compared with that on the copper substrate. The improved performance is proposed to be related to the presence of Cu mixed state and retention of morphology of the electrosprayed catalyst on the carbon paper, showing the importance of the substrate. In addition, the C2 product selectivity can be tuned by the electrospray synthesis time as it affects the size of the surface nanostructure as well as the porosity of the catalyst, which can provide an effective way to regulate the C2/C1 ratio.

Electrochemical oxidation processes can affect the electronic structure and activate the catalytic performance of precious-metal and transition-metal based catalysts for the oxygen evolution reaction (OER). Also there are emerging requirements to develop OER electrocatalysts under various pH conditions in order to couple with different reduction reactions. Herein, we studied the effect of pH on the electroactivation of IrNi alloy nanoparticles supported on carbon (IrNi/C) and evaluated the electrocatalytic activities of the activated IrNiOx/C for water oxidation under neutral conditions. In addition, their electronic structures and atomic arrangement were analyzed by in situ/operando X-ray absorption spectroscopy (XAS) and identical location transmission electron microscopy techniques, showing the reconstruction of the metal elements during electroactivation due to their different stabilities depending on the electrolyte pH. IrNiOx/C activated under neutral pH conditions showed a mildly oxidized thin IrOx shell. Meanwhile, IrNiOx/C activated in acidic and alkaline electrolytes showed Ni-leached IrOx and Ni-rich IrNiOx surfaces, respectively. Particularly, the surface of IrNiOx/C activated under alkaline conditions shows IrOx with a high d-band hole and NiOx with a high oxidation state leading to excellent OER catalytic activity in neutral media (η = 384 mV at 10 mA cm−2) whereas much lower OER activity was reported under alkaline or acid conditions. Our results, which showed that electrochemically activated catalysts under different pH conditions exhibit a unique electronic structure by modifying the initial alloy catalyst, can be applied for the design of catalysts suitable for various electrochemical reactions.

Single-atom catalysts (SACs) possess the potential to achieve unique catalytic properties and remarkable catalytic mass activity by utilizing low-coordination and unsaturated active sites. However, smaller particles tend to aggregate into clusters or particles owing to their high surface energy. In addition, support materials that have strong interactions with isolated metal atoms, extremely large surface areas, and electrochemical stability are required. Therefore, sufficient information about these factors is needed to synthesize and utilize SACs. Herein, we review the recent investigations and advances in SACs for the oxygen evolution reaction (OER). We present not only the structural characterization of SACs, but also in situ/operando spectroscopic techniques and computational research for SACs to understand the mechanism and reveal the origin of their excellent OER activity. Furthermore, the OER catalytic activity and stability of SACs are summarized to evaluate the current level of SACs. Currently, research on single-atoms as OER catalysts is in the infant stage for synthesis, characterization and mechanism studies. We discuss some challenges for understanding the fundamentals of SACs and enhancing the catalytic performance of SACs for industrial applications.

Hydrogen peroxide production by enhanced electrocatalysts is an attractive alternative to the present commercial process. While the subnano/atomic dispersion in noble metal nanocatalysts is known to strongly enhance their catalytic efficiency and chemoselectivity, their excessive surface energy and consequent coarsening seriously compromise their physical/chemical stability. Here, we report a subnano/atomically dispersed Pt–Ag alloy (by a simply modified polyol process) that is resistant to agglomeration/Ostwald ripening. This catalyst does not follow a conventional four-electron oxygen reduction reaction (ORR) but selectively produces H2O2 without excessive degradation of its activity. We clarified the role of the alloying element, Ag, as follows: (1) selective activation of two-electron ORR by inhibiting O2 dissociation and (2) suppression of H2O2 decomposition by preventing the H2O2 adsorption. The present approach provides a convenient route for the direct generation of H2O2 as a simple byproduct of electricity generation by fuel-cell systems.

The gradual increase in the atmospheric CO2 concentration is an urgent issue that poses a threat to human beings. Recently, the electrochemical CO2 reduction reaction (eCO2RR) has arisen as a promising and eco-friendly strategy for the storage of electricity from renewable sources as permanent chemical energy, as well as for the conversion of atmospheric CO2 into value-added chemicals. Among various catalysts, transition metals have been employed as heterogeneous electrocatalysts to yield valuable carbon chemicals such as carbon monoxide, formic acid, ethylene, and ethanol. Recent developments in catalysts and electrochemical devices have boosted catalytic activities and product selectivities, bringing the eCO2RR to practically promising levels. However, a lack of study to secure stable catalysts for eCO2RR remains a major obstacle for further progress of this technology. This review focuses on efforts to improve the electrochemical stability of catalysts. First, the catalyst deactivation process, including contaminations by metal impurities or carbon derivatives and changes in catalyst morphology during the eCO2RR, is discussed to understand the origin of insufficient stability. Next, recent progress in strategies for the preparation of highly stable catalyst systems will be presented. The discussion of valuable approaches that effectively prevent deactivation processes, such as the exclusion of metal impurities, periodic electrochemical activation, and the design of stable catalysts through the manipulation of various factors, allows identification of several clues for long-term stability. We hope that this review will inspire future catalyst design and stimulate the development of new ideas for the improvement of electrochemical stability.

In the electrochemical CO2 reduction reaction (CO2RR), Cu has been spotlighted as the only electro-catalyst that can produce multi-carbon molecules, but the mechanism of the selective C2+ production reaction remains elusive. Here, we directly monitored CO2RR intermediates by employing time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS), with particular attention to the C1 and C2+ pathways beyond the formation of *CO. Electrodeposited Cu and Cu(OH)2-derived Cu were synthesized, and subsequently employed as a C1 and C2+ activating catalyst and C2+ activating catalyst, respectively. For the first time, a kinetically linked dimer intermediate (*OCCO) was observed and identified as the C2+ path triggering intermediate. The ATR-SEIRAS results suggest that C–C coupling occurs exclusively by CO dimerization toward *OCCO, without the participation of *CHO, which is an intermediate for CH4 production. In the real-time measurements, CO dimerization occurred concurrently with CO adsorption (∼5 s), while proton-coupled reduction toward *CHO has slower kinetics (∼30 s). We demonstrated that the sites showing a high vibrational frequency of *CO on the fragmented Cu surface are the potential active sites for the fast dimerization of CO. This work provides mechanistic insights into the CO2RR pathways and enables the design of efficient C2+-producing catalysts.

The electrochemical reduction of CO2 stores intermittent renewable energy in valuable raw materials, such as chemicals and transportation fuels, while minimizing carbon emissions and promoting carbon-neutral cycles. Recent technoeconomic reports suggested economically feasible target products of CO2 electroreduction and the relative influence of key performance parameters such as faradaic efficiency (FE), current density, and overpotential in the practical industrial-scale applications. Furthermore, fundamental factors, such as available reaction pathways, shared intermediates, competing hydrogen evolution reaction, scaling relations of the intermediate binding energies, and CO2 mass transport limitations, should be considered in relation to the electrochemical CO2 reduction performance. Intensive research efforts have been devoted to designing and developing advanced electrocatalysts and improving mechanistic understanding. More recently, the research focus was extended to the catalyst environment, because the interfacial region can delicately modulate the catalytic activity and provide effective solutions to challenges that were not fully addressed in the material development studies. Herein, we discuss the importance of catalyst-electrolyte interfaces in improving key operational parameters based on kinetic equations. Furthermore, we extensively review previous studies on controlling organic modulators, electrolyte ions, electrode structures, as well as the three-phase boundary at the catalyst-electrolyte interface. The interfacial region modulates the electrocatalytic properties via electronic modification, intermediate stabilization, proton delivery regulation, catalyst structure modification, reactant concentration control, and mass transport regulation. We discuss the current understanding of the catalyst-electrolyte interface and its effect on the CO2 electroreduction activity.

Copper-based catalysts have attracted enormous attention due to their high selectivity for C

A photoelectrochemical (PEC) cell produces hydrogen energy using solar energy and an electrochemical reaction. In the hydrogen production process with water decomposition, electrons move from the anode to the cathode, and by measuring the current value at this time, the PEC cell can generate hydrogen and function as an image sensor at the same time. Due to the characteristics of the PEC cell that can perform both functions simultaneously, it can be applied as a device that can detect and respond to the surrounding environment without the need for an observation system such as a camera. We present the imaging performance of PEC cells. The effectiveness of the experiment was confirmed by applying the PEC cells to integral imaging, one of the three-dimensional (3D) imaging techniques.

Electrochemical conversion of CO

The ability to control the active edge sites of transition metal dichalcogenides (TMDs) is crucial for modulating their chemical activity for various electrochemical applications, including hydrogen evolution reactions. In this study, we demonstrate a colloidal synthetic method to prepare core-shell-like heterostructures composed of MoSe2 and WSe2 via a two-step sequential growth. By overgrowing WSe2 on the surface of preexisting MoSe2 nanosheet edges, MoSe2-core/WSe2-shell heterostructures were successfully obtained. Systematic comparisons of the secondary growth time and sequential order of growth suggest that the low synthetic temperature conditions allow the stable overgrowth of shells rich in WSe2 on top of the core of MoSe2 with low Gibbs formation energy. The electrochemical analysis confirms that the catalytic activity correlates to the core-shell composition variation. Our results propose a new strategy to control the edge site activity of TMD materials prepared by colloidal synthesis, which is applicable to diverse electrochemical applications.

Due to the global agenda to achieve net zero carbon emission, the needs to develop carbon capture and utilization technology has been sharply emerging. Although electrochemical CO2 reduction (CO2R) to useful carbon chemicals is challenging to meet the industrial requirements, recent studies have made a significant improvement in the performances both of the product selectivity and current density. Gas-diffusion electrode configurations allow direct CO2 gas-feeding to the catalyst layer and several hundred mA/cm2 of current density have been demonstrated with a zero-gap type of membrane electrolyzer assembly (MEA) electrolyzer. However, many underlying phenomena are still not clearly understood. Among various components of MEA, here, I will focus on the cathode catalyst, and balanced CO2 / water supply at the catalyst/membrane boundary to understand the CO2R activity. We demonstrate the importance of the water supply from the anolyte for the selective CO2R in the zero-gap MEA electrolyzer. We confirm that hydrogen is mostly originated from the aqueous anolyte for the production of the ethylene from CO2R with controlled labelling experiments. In terms of the Cu catalyst morphology, the alkaline environment near the catalyst layer leads a significant morphology changes during the pre-treatment steps for the ionomer activation, which contributes to increase in the CO2R activity. The microenvironment behavior is simulated and compares with the experimental CO2R MEA performance to understand the mass flow and CO2R activity, which also support the catalyst thickness dependence. For the practical application consideration, we also study the CO2R activity for CO production with the low concentration (~ 10%) of CO2 feeding and amine-captured direct CO2 reduction condition. Weak HER activity is important especially with the low concentration of CO2 because the slower CO2 reduction rate lead to more hydrogen compared to 100 % of CO2 gas feeding. These studies will give insight to the intrinsic and extrinsic factors determining the activities of CO2R MEA.