Electrocatalyst Materials Research Articles

Enhanced electrocatalytic CO2 reduction performance of Co‐porphyrin derivatives supported on CNTs with methylation of the hydroxyl and carboxyl groups

Metal‐porphyrin complexes with a well‐defined M‐N4 structure are a class of electrocatalyst materials that can be reasonably designed to exhibit high electrochemical carbon dioxide reduction (CO2RR) performance. The substituent effect of metal‐porphyrin complexes plays an important role in CO2RR. Herein, Co‐porphyrins with different substituents of ‐COOCH3, ‐OCH3, ‐COOH, and ‐OH (denoted as CoTCMePP, CoTOMePP, CoTCPP, and CoTOPP) were prepared and uniformly anchored on carbon nanotubes. CoTCMePP/CNTs exhibited a higher FE (CO) of 94.5% with a current density of 12.9 mA cm−2 and a TOF of 705 h−1 at −0.77 V versus RHE in 0.5 M KHCO3 than that of CoTCPP/CNTs. Meanwhile, the performance of CoTOMePP/CNTs was superior to CoTOPP/CNTs in FE (CO) and stability. The methylated derivatives exhibited enhanced electrocatalytic CO2 reduction performance, for the methylation of the hydroxyl and carboxyl might increase the solubility and suppress the aggregation of metal‐porphyrin, helping Co‐porphyrins disperse on the carbon nanotubes better.

Boosting Alkaline Hydrogen Evolution Reaction through Water Structure Manipulation.

In the past, the design of efficient electrocatalyst materials for alkaline hydrogen evolution reaction (HER) was mostly focused on tuning the adsorption properties of reaction intermediates. A recent breakthrough shows that the performance can be improved by manipulating water structure at the electrode-electrolyte interface using atomically localized electric fields. The new approach was realized by using IrRu dizygotic single-atom sites and led to a significantly accelerated water dissociation and an overall improved alkaline HER performance. Supported by extensive data from advanced modeling, characterization, and electrochemical measurements, the work delivers an intricate examination of the interaction between water molecules and the catalyst surface, thereby enriching our understanding of water dissociation kinetics and offering new insights to boost overall alkaline HER efficiency.

Boosting Alkaline Hydrogen Evolution Reaction through Water Structure Manipulation

AbstractIn the past, the design of efficient electrocatalyst materials for alkaline hydrogen evolution reaction (HER) was mostly focused on tuning the adsorption properties of reaction intermediates. A recent breakthrough shows that the performance can be improved by manipulating water structure at the electrode‐electrolyte interface using atomically localized electric fields. The new approach was realized by using IrRu dizygotic single‐atom sites and led to a significantly accelerated water dissociation and an overall improved alkaline HER performance. Supported by extensive data from advanced modeling, characterization, and electrochemical measurements, the work delivers an intricate examination of the interaction between water molecules and the catalyst surface, thereby enriching our understanding of water dissociation kinetics and offering new insights to boost overall alkaline HER efficiency.

Spatiotemporal Mapping of Local Heterogeneities during Electrochemical Carbon Dioxide Reduction.

The activity and selectivity of a copper electrocatalyst during the electrochemical CO2 reduction reaction (eCO2RR) are largely dominated by the interplay between local reaction environment, the catalyst surface, and the adsorbed intermediates. In situ characterization studies have revealed many aspects of this intimate relationship between surface reactivity and adsorbed species, but these investigations are often limited by the spatial and temporal resolution of the analytical technique of choice. Here, Raman spectroscopy with both space and time resolution was used to reveal the distribution of adsorbed species and potential reaction intermediates on a copper electrode during eCO2RR. Principal component analysis (PCA) of the in situ Raman spectra revealed that a working electrocatalyst exhibits spatial heterogeneities in adsorbed species, and that the electrode surface can be divided into CO-dominant (mainly located at dendrite structures) and C-C dominant regions (mainly located at the roughened electrode surface). Our spectral evaluation further showed that in the CO-dominant regions, linear CO was observed (as characterized by a band at ∼2090 cm-1), accompanied by the more classical Cu-CO bending and stretching vibrations located at ∼280 and ∼360 cm-1, respectively. In contrast, in the C-C directing region, these three Raman bands are suppressed, while at the same time a band at ∼495 cm-1 and a broad Cu-CO band at ∼2050 cm-1 dominate the Raman spectra. Furthermore, PCA revealed that anodization creates more C-C dominant regions, and labeling experiments confirmed that the 495 cm-1 band originates from the presence of a Cu-C intermediate. These results indicate that a copper electrode at work is very dynamic, thereby clearly displaying spatiotemporal heterogeneities, and that in situ micro-spectroscopic techniques are crucial for understanding the eCO2RR mechanism of working electrocatalyst materials.

Recent Advances in Metallic Catalyst Materials for Electrochemical Upgrading of Furfurals to Drop‐in Biofuels: A Mini Review

Electro‐organic synthesis is an ecologically benign and cost‐effective technique. Among other purposes, it can be used to produce a broad spectrum of biofuels for aviation applications. Metallic electrocatalyst materials employed for electro‐organic synthesis enable the conversion of biomass derived furfural compounds to various furanic biofuels. Each metallic catalyst material has its own inherent characteristics of generating specific amounts of fine chemicals and fuel components. By and large, furanic biofuels produced using metallic catalyst materials are favored explicitly under acidic or mildly acidic electrolytes. Therefore, it is intriguing to understand the nature of different catalyst materials that are compatible with acidic electrolytes. Herein, the focus will be on the recent progress in the field of electro‐organic synthesis of furanic fuels under acidic conditions. This review provides an overview of electrocatalytic conversion, its fundamentals, the reaction pathways observed during conversion, and the importance of metallic catalyst materials. Subsequently, the role of noble and nonnoble metallic catalysts on the electrocatalytic transformation of furfural compounds to various biofuels in acidic environment is discussed. In the end, perspectives are presented with regard to the challenges associated with the current technology and possible ways to look ahead to scale up the current technology.

3D Porous Nitrogen-rich Octahedral Carbon as advanced Oxygen Reduction Reaction catalyst

A Metal-organic-frameworks (MOFs) derived 3D porous nitrogen-rich octahedral carbon (PNOC) catalyst is successfully fabricated via carbonization of MIL-101(Fe) precursor process. As-obtained PNOC combines the advantages of high surface area, well permeable pore and rich nitrogen content in one catalyst, which shows excellent catalytic activity and stability for oxygen reduction reaction (ORR). This work would offer some new insights to advanced ORR electrocatalyst material designed in fuel cells.

Enhanced Hydrogen Evolution Reaction Performances of Ultrathin CuBi2O4 Nanoflakes

Semiconductor catalysts play a potential role for efficient electrocatalytic hydrogen production. In this work, copper bismuth oxide (CuBi2O4) nanostructures were synthesized via the coprecipitation method using two different Cu precursors: one is Cu(NO3)3·9H2O and the other is CuCl2. When using Cu(NO3)3·9H2O, the sample showed an interconnected and aggregated irregular spherical CuBi2O4 nanoparticle structure. On the other hand, the CuCl2-derived CuBi2O4 sample exhibited an interconnected ultrathin nanoflake structure. The CuBi2O4 nanoflakes displayed a higher electrochemically active surface area (160 cm2) than the CuBi2O4 nanoparticle (116 cm2). Accordingly, the CuBi2O4 nanoflakes revealed an excellent hydrogen evolution reaction performance with a low Tafel slope (117 mV/dec) and a small overpotential (384 mV at 10 mA/cm2 in 1 M KOH). These results specify that the CuBi2O4 nanoflakes are a suitable electrocatalyst material for high-performance water splitting.

Electronic and electrocatalytic applications based on solution‐processed two‐dimensional platinum diselenide with thickness‐dependent electronic properties

AbstractPlatinum diselenide (PtSe2) has shown great potential as a candidate two‐dimensional (2D) material for broadband photodetectors and electrocatalysts because of its unique properties compared to conventional 2D transition metal dichalcogenides. Synthesis of 2D PtSe2 with controlled layer number is critical for engineering the electronic behavior to be semiconducting or semimetallic for targeted applications. Electrochemical exfoliation has been investigated as a promising approach for mass‐producing in a cost‐effective manner, but obtaining high‐quality films with control over electronic properties remains difficult. Here, we demonstrate wafer‐scale 2D PtSe2 films with pre‐determined electronic types based on a facile solution‐based strategy. Semiconducting or semimetallic PtSe2 nanosheets with large lateral sizes are produced via electrochemically driven molecular intercalation, followed by centrifugation‐based thickness sorting. Finally, gate‐tunable broadband visible and near‐infrared photodetector arrays are realized based on semiconducting PtSe2 nanosheet films, while semimetallic films are used to create catalytic electrodes for overall water splitting with long‐term stability.image

Evolution of Vanadium Redox Flow Battery in Electrode.

The vanadium redox flow battery (VRFB) is a highly regarded technology for large-scale energy storage due to its outstanding features, such as scalability, efficiency, long lifespan, and site independence. This paper provides a comprehensive analysis of its performance in carbon-based electrodes, along with a comprehensive review of the system's principles and mechanisms. It discusses potential applications, recent industrial involvement, and economic factors associated with VRFB technology. The study also covers the latest advancements in VRFB electrodes, including electrode surface modification and electrocatalyst materials, and highlights their effects on the VRFB system's performance. Additionally, the potential of two-dimensional material MXene to enhance electrode performance is evaluated, and the author concludes that MXenes offer significant advantages for use in high-power VRFB at a low cost. Finally, the paper reviews the challenges and future development of VRFB technology.

Superhydrophilicity and Antifouling Behavior in Electrochemically Oxidized Nanocrystalline Pseudographite

Electrochemical oxidation of GUITAR (pseudoGraphite from the University of Idaho Thermolyzed Asphalt Reaction) produces a surface that exhibits superhydrophilic properties. This surface contains 20.7% relative oxygen abundance, giving it a heightened affinity for water relative to the pristine material. Scanning electron and atomic force micrographs reveal spherical, bubble-like structures on GUITAR, indicating a higher surface roughness (Rq = 300–400 nm) over the predominantly smooth titanium substrate (Rq = 94.5 nm). Combining an intrinsic affinity toward water with a heightened surface roughness produces a material with an apparent water contact angle of 0°. The synergistic effects of a superhydrophilic surface that can function as an electrode result in an electrocatalyst material that is highly resistant to fouling. When stored in water, oxidized GUITAR (Ox-GUITAR) completely resists fouling by volatile organic compounds for the duration of testing (72 h). When fouled directly with a drop of oil, the residue can be removed using a simple water rinse. The removal of oil residues from carbon surfaces is typically not possible without the use of solvents, surfactants, or mechanical exfoliation. This combination of properties opens Ox-GUITAR to a broad array of possible applications, such as implantable electrodes, field sensors, or water-quality monitoring.

Zinc Nanoparticles Electrodeposited on TiO2Nanotube Arrays Using Deep Eutectic Solvents for Implantable Electrochemical Sensors

This work reports on the electrodeposition of zinc on nanoporous metal oxide titania nanotube arrays (TiO2 NTAs) using a zinc-containing deep eutectic solvent (Zn2+–DES). The effects of substrate morphology and crystallinity, deposition temperature, zinc concentration, and deposition time on the morphology and electrochemical properties of the Zn/TiO2 NTAs were investigated. Two-dimensional zinc nanohexagons (NHexs) with a mean diameter of ∼300 nm and a thickness of 10–20 nm were decorated onto the TiO2 NTAs (with a pore diameter of ∼80 nm and a tube length of ∼5 μm) via electrodeposition at −1.6 V using Zn2+–DES. Cyclic voltammetry tests on the Zn2+–DES electrolyte revealed an electrochemical window of ∼3.5 V, and the diffusion coefficient of Zn2+ was found to be 4.29 × 10–10 cm2 s–1 at room temperature and 7.10 × 10–10 cm2 s–1 at 40 °C. Zinc nucleation on TiO2 NTA substrates followed an instantaneous model. Using a higher electrodeposition temperature increased the nucleation and growth rate of zinc NHexs, while annealing TiO2 NTAs was found to improve their uniformity and morphology. During the initial stage of deposition, hexagonal close-packed zinc NHexs were found to preferentially grow on tetragonal anatase TiO2 NTAs. The electrodeposition of zinc resulted in lowering the impedance and improving the overall electrochemical properties of TiO2 NTAs. The Zn/TiO2 NTAs developed in this study offer a promising electrocatalyst material system for implantable electrochemical sensors.

Nanocomposites with ZrO2@S-Doped g-C3N4 as an Enhanced Binder-Free Sensor: Synthesis and Characterization.

This study describes new electrocatalyst materials that can detect and reduce environmental pollutants. The synthesis and characterization of semiconductor nanocomposites (NCs) made from active ZrO2@S-doped g-C3N4 is presented. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) measurements were used to examine electron transfer characteristics of the synthesized samples. Using X-ray diffraction (XRD) and high-resolution scanning electron microscopy (HR-SEM) techniques, inclusion of monoclinic ZrO2 on flower-shaped S-doped-g-C3N4 was visualized. High-resolution X-ray photoelectron spectroscopy (XPS) revealed successful doping of ZrO2 into the lattice of S-doped g-C3N4. The electron transport mechanism between the electrolyte and the fluorine tin-oxide electrode (FTOE) was enhanced by the synergistic interaction between ZrO2 and S-doped g-C3N4 as co-modifiers. Development of a platform with improved conductivity based on an FTOE modified with ZrO2@S-doped g-C3N4 NCs resulted in an ideal platform for the detection of 4-nitrophenol (4-NP) in water. The electrocatalytic activity of the modified electrode was evaluated through determination of 4-NP by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions (pH 5). ZrO2@S-doped g-C3N4 (20%)/FTOE exhibited good electrocatalytic activity with a linear range from 10 to 100 μM and a low limit of detection (LOD) of 6.65 μM. Typical p-type semiconductor ZrO2@S-doped g-C3N4 NCs significantly impact the superior detection of 4-NP due to its size, shape, optical properties, specific surface area and effective separation of electron-hole pairs. We conclude that the superior electrochemical sensor behavior of the ZrO2@S-doped g-C3N4 (20%)/FTOE surfaces results from the synergistic interaction between S-doped g-C3N4 and ZrO2 surfaces that produce an active NC interface.

A new carbon allotrope: Biphenylene as promising anode materials for Li-ion and Li[sbnd]O2 batteries

Using first-principles computational approaches, we investigate a new carbon allotrope, biphenylene, composed of tetragonal, hexagonal, and octagonal carbon rings as a promising material for Li-ion and LiO2 batteries. We find the Li/C ratio is <1/6 for the single-layer biphenylene which is similar to that of graphene. However, it can reach to lithium composition of Li1C6, Li1C4.5, Li1C4, Li1C3.75, and Li1C3 for bi-, tri-, tetra-, penta-layer, and bulk biphenylene, respectively. It is also found that Li is very mobile on both single-layer and bi-layer biphenylene based on the calculation results of the interaction between Li and substrate and Li diffusion. In addition, we also elucidate the electrochemical performance via the discharge−charge mechanism using Li/biphenylene as electrocatalyst materials of LiO2 battery. Gibbs free energy diagram of the discharge-charge mechanism is illustrated to examine the electrochemical performance. Our results reveal that biphenylene network can be a promising and low-cost catalyst for both Li-ion and LiO2 batteries.

Recent advances in electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid: Mechanism, catalyst, coupling system

Abstract Catalytic synthesis of value-added chemicals from sustainable biomass or biomass-derived platform chemicals is an essential strategy for reducing dependency on fossil fuels. As a precursor for the synthesis of important polymers such as polyesters, polyurethanes, and polyamides, FDCA is a monomer with high added value. Meanwhile, due to its widespread use in chemical industry, 2,5-furandicarboxylic acid (FDCA) has gained significant interest in recent years. In this review, we discuss the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) and summarize the most recent advances in electrode materials from the past 5 years, including reaction mechanisms, catalyst structures, and coupling reactions. First, the effect of pH on the electrocatalytic oxidation of furfural is presented, followed by a systematic summary of the reaction mechanism (direct and indirect oxidation). Then, the advantages, disadvantages, and research progress of precious metal, non-precious metal, and non-metallic HMF electrooxidation catalysts are discussed. In addition, a coupled dual system that combines HMF electrooxidation with hydrogen reduction reaction, CO2 reduction, or N2 reduction for more effective energy utilization is discussed. This review can guide the electrochemical oxidation of furfural and the development of advanced electrocatalyst materials for the implementation and production of renewable resources.

Perovskite‐based electrocatalyst discovery and design using word embeddings from retrained SciBERT language model

AbstractWith the ever‐increasing volume of scientific literature, there is a strong need to develop methods that allow rigorous information identification. In this contribution, a state‐of‐the‐art natural language processing (NLP) model was used to select perovskite materials for electrocatalytic applications from literature. This was accomplished by obtaining word embeddings for perovskite materials from the NLP model and subsequently designing downstream tasks to discover perovskite‐based electrocatalyst materials. However, embeddings could be obtained only for materials available in the literature. Consequently, a novel methodology was devised to generate embeddings for newly designed materials. Results from the analysis showed that the computed embeddings could be used to rank materials for their suitability for electrocatalytic applications. Further, the word embeddings were also employed as features in predicting the electrocatalytic activity of perovskite‐based electrocatalysts. The analysis demonstrated that the fidelity of regression models increased when the embeddings were used as features.

Preparation of lotus-leaf-like carbon cathode for the electro-Fenton oxidation process: Hydrogen peroxide production, various organics degradation and printing wastewater treatment

To develop an electro-Fenton (EF) oxidation process for highly efficient organics degradation, a carbon cathode with lotus-leaf-like super-hydrophobic surface was prepared using ordinary graphite powder as an electro-catalyst material, polytetrafluoroethylene (PTFE) as an adhesive agent, boric acid (H3BO3) as a pore-forming agent, and using copper wire meshes to shape the surface morphology. The obtained results show that the carbon cathode with a lotus-leaf-like morphology led to an evident increase in hydrophobicity, which greatly enhanced hydrogen peroxide (H2O2) production performance. In the air-aerated Na2SO4 solution (pH = 2.8), the cathode prepared under optimized conditions yielded 527.5 mg L−1 H2O2 within 60 min with an observed current efficiency (CE) of 35.1 %. The developed EF oxidation process exhibited the strong oxidation ability for the degradation of several organics including rhodamine B (RhB), methylene blue trihydrate (MBT), p-nitrophenol (p-NP) and tetracycline (TC). What's more, the treatment of one real printing wastewater by this EF system presented the chemical oxygen demand (COD) removal of 76.8 % and the total organic carbon (TOC) removal of 73.5 %, and concurrently enhanced the biodegradability evidently. In addition, it was found that chloride ion (Cl−) might have an adverse effect on organics degradation due to the meaningless H2O2 consumption caused by HClO and ClO−. The results of this study indicate that the developed EF process can be used not only for the efficient removal of organic pollutants, but also as a pre-treatment before biological treatment for the enhancement of biodegradability.

Screening process provides a way of testing and identifying non-PGM catalyst materials

A US electrolyser company has developed a screening process for rapidly identifying alternatives to costly and scarce catalysts such as iridium and other rare platinum group metals (PGM) used in electrolysers to produce hydrogen. H2U Technologies Inc, based in Chatsworth, California, claims that its technology offers a clear pathway for the hydrogen industry to scale quickly without facing bottlenecks caused by a lack of material supply or volatile, high costs. Here we look at what this technology entails, briefly explain how it has been used to optimise catalysts for electrolyser stacks and report on a partnership that aims to address cost and supply chain issues for rare PGM electro-catalyst materials.

Impact of Different Lignin Sources on Nitrogen-Doped Porous Carbon toward the Electrocatalytic Oxygen Reduction Reaction.

Lignin is an ideal carbon source material, and lignin-based carbon materials have been widely used in electrochemical energy storage, catalysis, and other fields. To investigate the effects of different lignin sources on the performance of electrocatalytic oxygen reduction, different lignin-based nitrogen-doped porous carbon catalysts were prepared using enzymolytic lignin (EL), alkaline lignin (AL) and dealkaline lignin (DL) as carbon sources and melamine as a nitrogen source. The surface functional groups and thermal degradation properties of the three lignin samples were characterized, and the specific surface area, pore distribution, crystal structure, defect degree, N content, and configuration of the prepared carbon-based catalysts were also analyzed. The electrocatalytic results showed that the electrocatalytic oxygen reduction performance of the three lignin-based carbon catalysts was different, and the catalytic performance of N-DLC was poor, while the electrocatalytic performance of N-ELC was similar to that of N-ALC, both of which were excellent. The half-wave potential (E1/2) of N-ELC was 0.82 V, reaching more than 95% of the catalytic performance of commercial Pt/C (E1/2 = 0.86 V) and proving that EL can be used as an excellent carbon-based electrocatalyst material, similar to AL.

Carbon-Supported and Shape-Controlled PtPd Nanocrystal Synthesis in Flowing Deep Eutectic Solvents for the Methanol Oxidation Reaction

Practical applications of advanced nanocrystals are limited by the lack of low-cost, scalable, and environmentally friendly manufacturing methods with consistent shape and size control. To address this challenge, we demonstrate here the use of continuous-flow reactors and environmentally benign deep eutectic solvents for the shape-controlled synthesis of intermetallic PtPd nanocrystals with almost exclusive octahedral shape and an average size of 12.8 nm within only 6 min of reaction time, much faster than conventional methods. The critical roles of solvent species were elucidated using a family of deep eutectic solvent combinations. We further demonstrate the direct growth of these shaped nanocrystals on carbon using a one-step process by harnessing their strong interactions with a Co- and N-codoped carbon surface, thus avoiding the mandatory additional catalyst separation and loading steps with conventional methods. The produced PtPd nanocrystals exhibited outstanding performance toward the electrooxidation of methanol and reached an activity of 201 mA mg–1 along with improved stability, confirming the promise of our method for scalable and low-cost manufacturing of shape-controlled electrocatalyst materials.

Product Distribution Control Guided by a Microkinetic Analysis for CO Reduction at High-Flux Electrocatalysis Using Gas-Diffusion Cu Electrodes

In addition to the identity of the electrocatalyst materials, the catalytic performance is strongly influenced by the local steady-state environment perturbed by reaction conditions (pressure and temperature) and the operating current density. Strategies developed by the experiments at low current densities often cannot be simply extrapolated to practical high electrocatalytic performance achieving over 1 A cm–2. In this study, the detailed microkinetic analysis of high-flux electroreduction of CO was carefully examined over high-surface-area Cu-based electrocatalysts in the form of gas-diffusion electrodes (GDEs). The study includes Tafel analysis, kinetic isotope effects, and temperature and pressure dependence measurements to establish rate expressions based on elementary steps and interpret the reaction pathways. Further digesting the kinetic data as a function of CO partial pressure (PCO) and reaction temperature disclosed higher PCO favored n-propanol (n-PrOH) and acetate at the expense of C2H4 and C2H5OH, pinning down the optimal operating conditions to maximize the performance of a specific product at a given overpotential. These findings reinforce the importance of “beyond catalyst” phenomena in modern electrocatalysis.