Electrode Catalyst Research Articles

Crown ether as a bifunctional booster in electrochemical water splitting

Electrochemical water splitting using renewable energy is considered a key technology to mitigate global warming and to realize the hydrogen economy. Extensive efforts have been devoted to finding high-performance electrode catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) involved in electrochemical water splitting, whereas the research on added components in the electrolyte to boost HER and/or OER is very limited. In this work, we report the use of 18-crown ether-6 (18C6) in the electrolyte as a bifunctional booster in water splitting. The addition of 18C6 in alkaline electrolyte drastically boosts HER current density from −50 to −300 mA cm−2 at −0.3 V vs. RHE and OER current density from 25 to 250 mA cm−2 at 1.7 V vs. RHE on the Ni foam electrode. Combing DFT calculations and experimental characterizations, the functions of 18C6 in boosting HER and OER on nickel electrodes under the alkaline condition are revealed. This research demonstrates the potential of macrocycle molecules as electrolyte additives and opens up new opportunities for boosting the performance of water splitting.

Engineering charge redistribution on high-density RuCo nanoclusters loaded on N-doped graphite carbon as robust bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

A major challenge for the development of rechargeable Zn-air batteries (ZABs) is represented by the lack of effective bifunctional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this work, a high-density alloy nanocluster catalyst evenly loaded on N-doped porous sheet-like graphite carbon layer arrays (RuCo/NC) was fabricated by one-step electrochemical exfoliation, accelerating the active site exposure and mass transfer. RuCo/NC exhibited a lower reversible oxygen overpotential of 0.713 V for the OER / ORR compared to the benchmark Pt/C//RuO2 (0.755 V). Moreover, density functional theory (DFT) calculations revealed an optimized adsorption / desorption behavior of *OOH, *OH, and *O species caused by the charge redistribution between Ru and Co in RuCo/NC, which dramatically lowered the reaction energy barrier for the rate-limiting steps in ORR / OER. A home-assembled ZAB with a RuCo/NC air electrode catalyst exhibited a higher open-circuit voltage (OCV) of 1.422 V and a power density of 130 mW cm−2, exceeding those of Pt/C//RuO2 (OCV = 1.348 V, power density = 108 mW cm−2). This work introduces a promising method for fabricating hierarchical sheet-like carbon-based functional materials with potential application in fuel cells and water electrolysis.

Optimizing the Performance of Low-Loaded Electrodes for CO2-to-CO Conversion Directly from Capture Medium: A Comprehensive Parameter Analysis.

Gas-fed reactors for CO2 reduction processes are a solid technology to mitigate CO2 accumulation in the atmosphere. However, since it is necessary to feed them with a pure CO2 stream, a highly energy-demanding process is required to separate CO2 from the flue gasses. Recently introduced bicarbonate zero-gap flow reactors are a valid solution to integrate carbon capture and valorization, with them being able to convert the CO2 capture medium (i.e., the bicarbonate solution) into added-value chemicals, such as CO, thus avoiding this expensive separation process. We report here a study on the influence of the electrode structure on the performance of a bicarbonate reactor in terms of Faradaic efficiency, activity, and CO2 utilization. In particular, the effect of catalyst mass loading and electrode permeability on bicarbonate electrolysis was investigated by exploiting three commercial carbon supports, and the results obtained were deepened via electrochemical impedance spectroscopy, which is introduced for the first time in the field of bicarbonate electrolyzers. As an outcome of the study, a novel low-loaded silver-based electrode fabricated via the sputtering deposition technique is proposed. The silver mass loading was optimized by increasing it from 116 μg/cm2 to 565 μg/cm2, thereby obtaining an important enhancement in selectivity (from 55% to 77%) and activity, while a further rise to 1.13 mg/cm2 did not provide significant improvements. The tremendous effect of the electrode permeability on activity and proficiency in releasing CO2 from the bicarbonate solution was shown. Hence, an increase in electrode permeability doubled the activity and boosted the production of in situ CO2 by 40%. The optimized Ag-electrode provided Faradaic efficiencies for CO close to 80% at a cell voltage of 3 V and under ambient conditions, with silver loading of 565 μg/cm2, the lowest value ever reported in the literature so far.

Accelerating Electricity Generation and Cr (VI) Removal Using Anatase–Biochar-Modified Cathode Microbial Fuel Cells

Microbial fuel cells (MFC) have considerable potential in the field of energy production and pollutant treatment. However, a low power generation performance remains a significant bottleneck for MFCs. Biochar and anatase are anticipated to emerge as novel cathode catalytic materials due to their distinctive physicochemical properties and functional group architectures. In this study, biochar was utilized as a support for an anatase cathode to investigate the enhancement of the MFC power generation performance and its environmental impact. The results of the SEM and XPS experiments showed that the biochar-supported anatase composites were successfully prepared. Using the new cathode catalyst, the maximum current density and power density of the MFC reached 164 mA/m2 and 10.34 W/m2, respectively, which increased by 133% and 265% compared to a graphite cathode (70.51 mA/m2 and 2.83 W/m2). The degradation efficiency of Cr (VI) was 3.1 times higher in the biochar-supported anatase MFC than in the graphite cathode. The concentration and pH gradient experiments revealed that the degradation efficiency of Cr (VI) was 97.05% at an initial concentration of 10 mg/L, whereas a pH value of two resulted in a degradation efficiency of 94.275%. The biochar-supported anatase composites avoided anatase agglomeration and provided more active sites, thus accelerating the cathode electron transfer. In this study, natural anatase and biochar were ingeniously combined to fabricate a green and efficient electrode catalyst, offering a novel approach for the preparation of high-performance positive catalysts as well as a sustainable, economical, and environmentally friendly method for Cr (VI) removal in aqueous solutions.

Creating Conjugated C-C Bonds between Commercial Carbon Electrode and Molecular Catalyst for Oxygen Reduction to Hydrogen Peroxide.

Immobilizing molecular catalysts on electrodes is vital for electrochemical applications. However, creating robust electrode-catalyst interactions while maintaining good catalytic performance and rapid electron transfer is challenging. Here, without introducing any foreign elements, we show a bottom-up synthetic approach of constructing the conjugated C-C bond between the commercial Vulcan carbon electrode and an organometallic catalyst. Characterization results from FTIR, XPS, aberration-corrected TEM and EPR confirmed the successful and uniform heterogenization of the complex. The synthesized Vulcan-LN4 -Co catalyst is highly active and selective in the oxygen reduction reaction in neutral media, showing an 80 % hydrogen peroxide selectivity and a 0.72 V (vs. RHE) onset potential which significantly outperformed the homogenous counterpart. Based on single-crystal XRD and NMR data, we built a model for density functional theory calculations which showed a nearly optimal binding energy for the *OOH intermediate. Our results show that the direct conjugated C-C bonding is an effective approach for heterogenizing molecular catalysts on carbon, opening new opportunities for employing molecular catalysts in electrochemical applications.

Colloid synthesis of Ni12P5/N, S-doped graphene as efficient bifunctional catalyst for alkaline hydrogen evolution and triiodide reduction reaction

Designing high-efficient bifunction catalysts with excellent catalytic activity and enhanced charge-transfer capability in both alkaline hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR) is of utmost significance to advance the development of green hydrogen production and photovoltaics, respectively, yet remains a crucial challenge. Here, highly dispersed and small-sized Ni12P5 nanocrystals with narrow size distribution was well attached on the surface of N, S co-doped graphene (Ni12P5/NSG) by the facile hot-injection method. As expected, the optimized Ni12P5/NSG requires a relatively low overpotential of 132.94 ± 0.08 mV to deliver a current density of 10 mA cm−2 in alkaline condition, accompanied with remarkable long-time durability with negligible attenuation over 50 h. Density functional theory (DFT) calculations revealed that the positively synergic effect between Ni12P5 and NSG are in favor of modulating the rate determining step of the dissociation of H2O to *(OH-H), thereby upgrading its HER activity. When used as the counter electrode catalyst for IRR in DSSCs, the resultant Ni12P5/NSG exhibits extraordinary Pt-like catalytic activity and well electrochemical stability in iodide-based electrolyte, delivering a high photoelectric conversion performance (PCE) comparable to Pt. The improved PCE can be attributed to the accelerated interfacial charge-transfer capability around active sites for facilitating the reaction kinetics of IRR, as demonstrated by DFT calculations. This work provides an effective strategy for synthesizing cost-effective composites with multi-active sites and offering valuable insight into the structure-performance relationship, which is conducive to guide the synthesis of promising catalysts in the energy conversion field.

Synthesis of plasmonic W18O49 interconnected nanowire frameworks with strong photo-enhanced hydrogen evolution reaction activity

The synthesis of high-order tungsten oxide nanowire frameworks (NWFs) is achieved using an unordinary stable molecular precursor formed by mixing tungsten hexachloride with methanol. The solvothermally obtained NWFs are well characterized with diffraction, microscopy, and nitrogen adsorption techniques. Time-resolved absorption spectroscopy and proton activity measurements reveal the stability of tungsten precursors in methanol. In butanol, the precursor decomposes rapidly into solid hydrated tungsten oxide and leads to the formation of freestanding nanowires (FNWs) after the solvothermal treatment. The NWFs show a blue shift in their characteristic plasmonic absorption wavelength when compared with FNWs. Such phenomenon is attributed to the high population of connecting nodes, which are postulated to be the plasmonic hot spots where the light-induced electromagnetic fields are amplified. The photo-deposition of palladium nanoparticles was hence selectively formed on these connecting nodes on the NWFs while showing no apparent selectivity on the FNWs. Furthermore, when applied as an electrode catalyst for the hydrogen evolution reaction, the NWFs demonstrated a much stronger photo-induced enhancement compared with the FNWs. The photo-induced effects demonstrate the advantage of plasmonic field enhancement through connected nanowires which can be obtained through a facile synthesis process.

Efficient NH3-Tolerant Nickel-Based Hydrogen Oxidation Catalyst for Anion Exchange Membrane Fuel Cells.

Converting hydrogen chemical energy into electrical energy by fuel cells offers high efficiencies and environmental advantages, but ultrapure hydrogen (over 99.97%) is required; otherwise, the electrode catalysts, typically platinum on carbon (Pt/C), will be poisoned by impurity gases such as ammonia (NH3). Here we demonstrate remarkable NH3 resistivity over a nickel-molybdenum alloy (MoNi4) modulated by chromium (Cr) dopants. The resultant Cr-MoNi4 exhibits high activity toward alkaline hydrogen oxidation and can undergo 10,000 cycles without apparent activity decay in the presence of 2 ppm of NH3. Furthermore, a fuel cell assembled with this catalyst retains 95% of the initial peak power density even when NH3 (10 ppm)/H2 was fed, whereas the power output reduces to 61% of the initial value for the Pt/C catalyst. Experimental and theoretical studies reveal that the Cr modifier not only creates electron-rich states that restrain lone-pair electron donation but also downshifts the d-band center to suppress d-electron back-donation, synergistically weakening NH3 adsorption.

Preparation of Double‐Layer Hollow Porous Carbon Microspheres by a Hydrothermal Method

AbstractDouble‐layer hollow porous carbon microspheres (DPCMs) with high specific surface area (up to 57.3 m2/g) were synthesized by a hydrothermal method using sucrose as the carbon source, SnCl4 ⋅ 5H2O as the porogen, and sodium dodecyl sulfate and sodium polyacrylate as the anionic surfactant and dispersant, respectively. The thickness and morphology of the inner and outer layers of the DPCMs (spherical, bowl‐like, mushroom‐like, or ellipsoidal) could be adjusted by changing the hydrothermal conditions. X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared analysis (FTIR) showed that the surface of the DPCMs was rich in −OH and −COOH functional groups, which was beneficial for subsequent chemical modification of the DPCMs. Because the prepared DPCM had a reactive surface layer and a stable carbonaceous double‐layer structure, the material could be used in supercapacitors and biochemistry, and as catalyst carriers, adsorption materials, and electrode materials, among other applications.

Ultra-Low Loading of Iron Oxide and Platinum on CVD-Graphene Composites as Effective Electrode Catalysts for Solid Acid Fuel Cells

We propose a new design for electrocatalysts consisting of two electrocatalysts (platinum and iron oxide) that are deposited on the surfaces of an oxidized graphene substrate. This design is based on a simple structure where the catalysts were deposited separately on both sides of oxidized graphene substrate; while the iron oxide precipitated out of the etching solution on the bottom-side, the surface of the oxidized graphene substrate was decorated with platinum using the atomic layer deposition technique. The Fe2O3-decorated CVD-graphene composite exhibited better hydrogen electrooxidation performance (area-normalized electrode resistance (ANR) of ~600 Ω·cm−2) and superior stability in comparison with bare-graphene samples (ANR of ~5800 Ω·cm−2). Electrochemical impedance measurements in humidified hydrogen at 240 °C for (Fe2O3|Graphene|Platinum) electrodes show ANR of ~0.06 Ω·cm−2 for a platinum loading of ~60 µgPt·cm−2 and Fe2O3 loading of ~2.4 µgFe·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. This ANR value is ~30% lower than the charge transfer resistance of the same electrode composition in the absence of Fe2O3 nanoparticles. Detailed study of the Fe2O3 electrocatalytic properties reveals a significant improvement in the electrode’s activity and performance stability with the addition of iron ions to the platinum-decorated oxidized graphene cathodes, indicating that these hybrid (Fe2O3|Graphene|Platinum) materials may serve as highly efficient catalysts for solid acid fuel cells and beyond.

Efficient Fe3C-CF Cathode Catalyst Based on the Formation/Decomposition of Li2-xO2 for Li-O2 Batteries.

Lithium-oxygen batteries have attracted considerable attention in the past several years due to their ultra-high theoretical energy density. However, there are still many serious issues that must be addressed before considering practical applications, including the sluggish oxygen redox kinetics, the limited capacity far from the theoretical value, and the poor cycle stability. This study proposes a surface modification strategy that can enhance the catalytic activity by loading Fe3C particles on carbon fibers, and the microstructure of Fe3C particle-modified carbon fibers is studied by multiple materials characterization methods. Experiments and density functional theory (DFT) calculations show that the discharge products on the Fe3C carbon fiber (Fe3C-CF) cathode are mainly Li2-xO2. Fe3C-CF exhibits high catalytic ability based on its promotion of the formation/decomposition processes of Li2-xO2. Consequently, the well-designed electrode catalyst exhibits a large specific capacity of 17,653.1 mAh g-1 and an excellent cyclability of 263 cycles at a current of 200 mA g-1.

A hierarchical strategy for fabricating synergistic 3D network bio-based porous carbon and 0D niobium-based bimetallic oxides as counter electrodes for I- and Cu-mediated dye-sensitized solar cells with N719 and Y123 dyes

Designing cost-effective counter electrode (CE) catalysts with advanced nanostructures and exploring their application in different dye-electrolyte systems is crucial for the development of dye-sensitized solar cells (DSSCs). In this work, two types of 3D network bio-based porous carbon (3D-BPC) loaded 0D niobium-based bimetallic oxide nanohybrids (CoNb2O6/3D-BPC and NiNb2O6/3D-BPC) were synthesized using a hierarchical strategy. Benefiting from the optimization of the electron transport pathways and enrichment of catalytically active sites via the hierarchical 0D/3D structure, formed by 3D-BPC and MNb2O6 (M = Co, Ni), the catalytic reduction ability of MNb2O6/3D-BPC was significantly enhanced. To explore the photovoltaic performance of the MNb2O6/3D-BPC based DSSC, the I3−/I− electrolyte and N719 dye system and the Cu2+/Cu+ electrolyte and Y123 dye system were simultaneously employed. The solar cells assembled with the CoNb2O6/3D-BPC and NiNb2O6/3D-BPC CE exhibited device efficiencies of 7.03% and 7.14% in the N719-I3−/I− system, respectively, and 1.84% and 2.42% in the Y123-Cu2+/Cu+ system, respectively, which were almost equal to those of Pt under the same system. Additionally, MNb2O6/3D-BPC catalysts exhibited promising stability in I3−/I− electrolyte. This work provides guidance for the construction of low-cost and high-efficiency nanohybrid catalysts for new energy conversion devices.

The carbon-doped Fe3O4 montmorillonite particle electrode for the degradation of antiviral drugs in electro-Fenton system

Since the outbreak of COVID-19, the extensive use of epidemic control drugs such as Arbidol (ARB) and Acyclovir (ACV) has significantly increased and the environmental pollution caused by these residues has attracted increasing attention. In this article, a novel montmorillonite graphene-like carbon hybrid Fe3O4 compound (Mt/GH/Fe3O4) as particle electrode catalyst was prepared and applied in three-dimensional-electro-Fenton (3D-EF) for the ARB and ACV degradation. The structure and composition of the compound catalyst were characterized. The degradation efficiency of targets was significantly increased in the 3D-EF degradation system and even more thorough for the degradation of targets, compared with simple 2D, 3D, and EF catalytic degradation systems. The degradation rate of antiviral drugs can reach >90% in 5 min with excellent stability. The research demonstrated that the clay mineral with a special structure loaded with graphene-like carbon and Fe3O4 had supplied an ideal reaction medium for the electro-Fenton reaction. Mt./GH/Fe3O4-based 3D-EF degradation system would have promising applications in the degradation and removal of antiviral drug residuals in the environment.

Nickel-Cobalt oxides coated on polypyrrole nanotubes as bifunctional electrode catalyst for enhancing the performance of the microbial fuel cells

The surface modification of electrodes is a vital technique for improving the power output of microbial fuel cells (MFCs). In this study, a single bifunctional catalyst material, Nickel (Ni)-cobalt (Co) oxides coated on polypyrrole nanotubes (PNT) (NiCo2O4@PNT), is prepare and used as the electrode catalyst material for a single chambered MFC. The catalyst show excellent oxygen reduction reaction (ORR) activity and work as a good electron acceptor at the anode. The electrocatalytic activity of the prepared catalyst is inspected by cyclic voltammetry (CV), which showed the highest reduction peak for NiCo2O4@PNT at 0.0621 mA. Four different catalysts have been prepare in this study NiCo2O4@PNT, NiO@PNT, CoO@PNT and PNT. The maximum power density of NiCo2O4@PNT is 427.52 mW/m2 (anode) and 916.12 mW/m2 (cathode), which is significantly higher than those of the other catalysts. These results suggest that NiCo2O4@PNT is a promising bifunctional catalyst for MFCs.

Tailoring Oxygen Reduction Reaction Kinetics on Perovskite Oxides via Oxygen Vacancies for Low-Temperature and Knittable Zinc-Air Batteries.

High kinetics oxygen reduction reaction (ORR) electrocatalysts under low temperature are critical and highly desired for temperature-tolerant energy conversion and storage devices, but remain insufficiently investigated. Herein, oxygen vacancy-rich porous perovskite oxide (CaMnO3 ) nanofibers coated with reduced graphene oxide coating (V-CMO/rGO) are developed as the air electrode catalyst for low-temperature and knittable Zn-air batteries. V-CMO/rGO exhibits top-level ORR activity among perovskite oxides and shows impressive kinetics under low temperature. Experimental and theoretical calculation results reveal that the synergistic effect between metal atoms and oxygen vacancies, as well as the accelerated kinetics, enhanced electric conductivity and mass transfer over the rGO coated nanofiber 3D network contribute to the enhanced catalytic activity. The desorption of ORR intermediate is promoted by the regulated electron filling. The V-CMO/rGO drives knittable and flexible Zn-air batteries under a low temperature of -40 °C with high peak power density of 56 mW cm-2 and long cycle life of over 80 h. This study provides insight of kinetically active catalyst and facilitates the ZABs application in harsh environment. This article is protected by copyright. All rights reserved.

Toward the Long-Term Stability of Cobalt Benzoate Confined Highly Dispersed PtCo Alloy Supported on a Nitrogen-Doped Carbon Nanosheet/Fe3C Nanoparticle Hybrid as a Multifunctional Catalyst for Zinc-Air Batteries.

This work reports a new type of platinum-based heterostructural electrode catalyst that highly dispersed PtCo alloy nanoparticles (NPs) confined in cobalt benzoate (Co-BA) nanowires are supported on a nitrogen-doped ultra-thin carbon nanosheet/Fe3C hybrid (PtCo@Co-BA-Fe3C/NC) to show high electrochemical activity and long-term stability. One-dimensional Co-BA nanowires could alleviate the shedding and agglomeration of PtCo alloy NPs during the reaction so as to achieve satisfactory long-term durability. Moreover, the synergistic effect at the interface optimizes the surface electronic structure and prominently accelerates the electrochemical kinetics. The oxygen reduction reaction half-wave potential is 0.923 V, and the oxygen evolution reaction under the condition of 10 mA•cm-2 is 1.48 V. Higher power density (263.12 mW•cm-2), narrowed voltage gap (0.49 V), and specific capacity (808.5 mAh•g-1) for PtCo@Co-BA-Fe3C/NC in Zn-air batteries are achieved with long-term cycling measurements over 776 h, which is obviously better than the Pt/C + RuO2 catalyst. The interfacial electronic interaction of PtCo@Co-BA-Fe3C/NC is investigated, which can accelerate electron transfer from Fe to Pt. Density functional theory calculations also indicate that the interfacial potential regulates the binding energies of the intermediates to achieve the best performance.

Simple Synthesis of AuPd Aerogel as a Self-Supporting Electrocatalysts with Excellent Performance

Direct ethanol fuel cell (DEFC) has the advantages of low pollution emissions, easy to carry, and high energy density. However, the development of fuel cells is limited due to the low catalytic activity and poor stability of electrode catalyst materials. Precious metal aerogels not only have three-dimensional self-supporting network structures but also have excellent properties of precious metals, which have very good catalytic efficiency for ethanol. In this study, bimetallic aerogels with varying Au/Pd ratios were prepared, and their impact on the electrocatalytic performance of ethanol was investigated.

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Electrochemical Promotion of CO2 Hydrogenation Using a Pt/YSZ Fuel Cell Type Reactor.

The hydrogenation of CO2 is a reaction of key technological and environmental importance, as it contributes to the sustainable production of fuels while assisting in the reduction of a major greenhouse gas. The reaction has received substantial attention over the years within the catalysis and electrocatalysis communities. In this respect, the electrochemical promotion of catalysis (EPOC) has been applied successfully to the CO2 hydrogenation reaction to improve the catalytic activity and selectivity of conductive films supported on solid electrolytes. However, designing an effective electrocatalytic reactor remains a challenge due to the connections required between the electrodes and the external potentiostat/galvanostat. This drawback could be alleviated if the catalytic reaction occurs in a reactor that simultaneously operates as a power generator. In this work, the Electrochemical Promotion of the CO2 hydrogenation reaction in a low-temperature solid oxide electrolyte fuel cell (SOFC) reactor is studied using yttria-stabilized zirconia (YSZ) and a platinum (Pt) electrode catalyst. The system has been studied in two distinct operation modes: (i) when the necessary energy for the electrochemical promotion is produced through the parallel reaction of H2 oxidation (galvanic operation) and (ii) when a galvanostat/potentiostat is used to impose the necessary potential (electrolytic operation). The performance of the fuel cell declines less than 15% in the presence of the reactant mixture (CO2 and H2) while producing enough current to conduct EPOC experiments. During the electrolytic operation of the electrochemical cell, the CO production rate is significantly increased by up to 50%.

Wood-derived pore-rich carbon: A green catalyst for counter electrodes of dye-sensitized solar cells

Common Pt-based electrocatalysts have the disadvantages of high cost and easy deactivation. The research focus will be the development of carbon-based counter electrodes (CEs) due to the high conductivity and stability in the electrolytes. This paper prepares a kind of CE with wood-derived pore-rich carbon (WDPRC), which uses poplar as the precursor and activates with KOH at different temperatures (700, 800, and 900 °C). 800-WDPRC (800 represents temperature) had a large specific surface area of 1234.30 m2/g, which shows that it has a rich pore structure, and provides more active sites for the reaction. And the DSSCs’ PCE with 800-WDPRC (5.99%) is higher than the wood-derived carbon (WDC) (carbonize at 800 °C and without activation) (2.32%). As for the CEs’ materials, the WDPRCs’ manufacturing process is simple (only two steps), and the materials used are environment-friendly and low in price. Therefore, this paper provides a new idea for preparing clean and efficient DSSCs’ CEs.