High Electrochemical Active Surface Area Research Articles

Achieving Exceptional Volumetric Desalination Capacity Using Compact MoS2 Nanolaminates.

Capacitive deionization (CDI) has emerged as a promising technology for freshwater recovery from low-salinity brackish water. It is still inapplicable in specific scenarios (e.g., households, islands, or offshore platforms) due to too low volumetric adsorption capacities. In this study, we report a high-density semi-metallic molybdenum disulfide (1T'-MoS2) electrode with compact architecture obtained by restacking of exfoliated nanosheets, which achieved high capacitance up to ∼277.5 F cm-3 under an ultrahigh scan rate of 1000mV s-1 with a lower charge-transfer resistance and nearly ten-fold higher electrochemical active surface area than the 2H-MoS2 electrode. Furthermore, 1T'-MoS2 electrode demonstrates exceptional volumetric desalination capacity of 65.1 mgNaCl cm-3 in CDI experiments. Ex-situ X-ray diffraction (XRD) reveal that the cation storage mechanism with the dynamic expansion of 1T'-MoS2 interlayer to accommodate cations such as Na+, K+, Ca2+, and Mg2+, which in turn enhances the capacity. Theoretical analysis unveils that 1T' phase is thermodynamically preferable over 2H phase, the ion hydration and channel confinement also play critical role in enhancing ion adsorption. Overall, this work provides a new method to design compact two-dimensional layered nanolaminates with high volumetric performance for CDI desalination. This article is protected by copyright. All rights reserved.

Controllable boosting activity on Co4N by Fe substitution for oxygen evolution reaction and efficient 5-hydroxymethylfurfural oxidation

The design of transition metal nitrides with excellent oxygen evolution reaction and 5-hydroxymethylfurfural oxidation reaction (HMFOR) is of great significance to achieve the goal of "carbon peaking and carbon neutrality". Herein, Fe-doped bimetallic nitride FexCo1-x)4N was prepared by a simple electron regulation strategy. The introduction of Fe changes the electronic structure of Co and optimizes the adsorption energies of *OH, reduces the potential barrier for the generation of *OOH as a potential-determining step and thus increases the intrinsic OER activity of Co4N. In addition, Fe substitution of some of the Co atoms gives (FexCo1-x)4N a higher electrochemical active surface area, which accelerates the electron transfer efficiency and improves the electrical conductivity. The overpotential for (FexCo1-x)4N-0.9 to reach a current density of 10 mA cm−2 in 1 M KOH is only 271 mV. When in 1 M KOH + 50 mM HMF condition, (FexCo1-x)4N-0.9 requires only 1.37 V to reach a current density of 10 mA cm−2. This work provides practical guidance for developing bifunctional transition metal electrocatalysts with excellent OER and HMFOR activity.

Electrocatalytic sensing of propyl gallate in real-time food samples using a synergistic Sm-MOF@GCN composite modified glassy carbon electrode

A novel electrochemical sensor has been developed using the sonochemically synthesized samarium metal–organic framework (Sm-MOF) and the graphitic carbon nitride (GCN) composite for the selective determination of propyl gallate (PG). The as-synthesized Sm-MOF@GCN composite was characterized by XRD, XPS, and FESEM. The morphological studies of the prepared Sm-MOF@GCN composite revealed the bar-shaped Sm-MOF and porous sheet-like morphology of GCN. The combined effect of the Sm-MOF and GCN enhance the current density response and lowers the oxidation potential, which was beneficial for the electrochemical sensing of PG. Moreover, the high electrochemical active surface area (EASA) (0.0649 cm2) and the rate constant value (Ko) of 1.44x10-5 cm s−1 confirm the faster electron transfer kinetics at the interface of Sm-MOF@GCN composite. However, the developed Sm-MOF@GCN composite possesses linear range from 0.02 to 60 µM with a nanomolar detection level (2.05 nM), high sensitivity (0.1914 μA μM−1 cm−2), excellent reproducibility, repeatability, and stability for up to 30 days towards the PG detection. Finally, the Sm-MOF@GCN composite-modified electrocatalyst was utilized for the quantification of PG in foodstuffs such as instant noodles, cookies, cakes, and oils. The result of the study, the Sm-MOF@GCN composite displayed good recovery results, making it a promising candidate for detecting PG in real-world samples in view of its binder-free approach and facile fabrication process.

Preparation of highly active and durable electrodes for alkaline water electrolysis by anodizing of commercial FeNi and FeNiCo alloys

Anodizing is gaining popularity as a binder-free fabrication route for obtaining catalyst materials directly on the current collector without using noble metals, binders, or conductive carbon additives. Here, we fabricate promising highly active electrodes for alkaline water electrolysis by anodizing commercial FeNi and FeNiCo alloys (%wt. Fe range between 22 and 63) in an ethylene glycol-based fluoride electrolyte. Anodizing forms metal fluoride coatings, which are converted to OER active compounds (γ-NiOOH:Fe) during potential cycling in an alkaline aqueous solution (1 mol L−1 (M) KOH at 293 K) as a result of leaching of fluoride ions. The morphology, thickness, and number of active sites are influenced by the amount of Fe in the alloy, and the electrode with the highest electrochemical active surface area (Kovar alloy with a 54 %wt. Fe) shows the largest OER activity enhancement by anodizing. The performance evaluation in practical conditions (7 mol L−1 KOH at 343 K) demonstrated a highly active performance with an OER potential as low as 1.52 V at a current density of 600 mA cm−2 even for electrodes obtained in alloys with a low amount of Fe (78-Permalloy with a 22 %wt. Fe), demonstrating that anodizing is an effective way to develop highly active OER electrodes from commercially available alloys. On the other hand, anodizing is a good fluoridation route for transition metals with good results in the formation of F-enriched precursors that efficiently promote active phase formation during the catalytic process, offering the possibility of obtaining catalysts directly on the current collector in a one-step process, easily implemented in industrial applications.

Green and sustainable use of macadamia nuts as support material in Pt-based direct methanol fuel cells

The successful commercialization of direct methanol fuel cells (DMFCs) is hindered by inadequate methanol oxidation activity and anode catalyst longevity. Efficient and cost-effective electrode materials are imperative in the widespread use of DMFCs. While Platinum (Pt) remains the primary component of anodic methanol oxidation reaction (MOR) electrocatalysts, its utilization alone in DMFC systems is limited due to carbon monoxide (CO) poisoning, instability, methanol crossover, and high cost. These limitations impede the economic feasibility of Pt as an electrocatalyst. Herein, we present the use of powdered activated carbon (PAC) and granular activated carbon (GAC), both sourced from macadamia nut shells (MNS), a type of biomass. These bio-based carbon materials are integrated into hybrid supports with reduced graphene oxide (rGO), aiming to enhance the performance and reduce the production cost of the Pt electrocatalyst. Electrochemical and physicochemical characterizations of the synthesized catalysts, including Pt-rGO/PAC-1:1, Pt-rGO/PAC-1:2, Pt-rGO/GAC-1:1, and Pt-rGO/GAC-1:2, were conducted. X-ray diffraction analysis revealed crystallite sizes ranging from 1.18 nm to 1.68 nm. High-resolution transmission electron microscopy (HRTEM) images with average particle sizes ranging from 1.91 nm to 2.72 nm demonstrated spherical dispersion of Pt nanoparticles with some agglomeration across all catalysts. The electrochemical active surface area (ECSA) was determined, with Pt-rGO/GAC-1:1 exhibiting the highest ECSA of 73.53 m2 g−1. Despite its high ECSA, Pt-rGO/GAC-1:1 displayed the lowest methanol oxidation reaction (MOR) current density, indicating active sites with poor catalytic efficiency. Pt-rGO/PAC-1:1 and Pt-rGO/PAC-1:2 exhibited the highest MOR current densities of 0.77 mA*cm−2 and 0.74 mA*cm−2, respectively. Moreover, Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 demonstrated superior electrocatalytic mass (specific) activities of 7.55 mA/mg (0.025 mA*cm−2) and 7.25 mA/mg (0.021 mA*cm−2), respectively. Chronoamperometry tests revealed Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 as the most stable catalysts. Additionally, they exhibited the lowest charge transfer resistances and highest MOR current densities after durability tests, highlighting their potential for DMFC applications. The synthesized Pt supported on PACs hybrids demonstrated remarkable catalytic performance, stability, and CO tolerance, highlighting their potential for enhancing DMFC efficiency.

Insights into synergetic modulation of nickel sites over graphene by introducing tungsten and light for efficient methanol electrooxidation

Cut-lost, highly active and stable (photo-)electrocatalysts are earnestly expected to overcome high energy obstacles in methanol oxidation reaction (MOR). A hybrid of NiW/graphene (NiW/G) is prepared by a simple self-designed electrosynthesis method. During the process of electrosynthesis, exfoliation of bulky graphite into graphene and generation of multivalent NiW bimetal precursor are both achieved. This obtained composite displays superior photoelectrocatalytic performance towards MOR. As for NiW/G-light, its area activity (peak current) and mass activity (peak current) are up to 343.4 mA cm−2 and 5960.7 mA mg−1 respectively, much higher than NiW/G, Ni/G and W/G. Operando electrochemical impedance spectroscopy, in-situ Fourier transform infrared spectroscopy and other ex-situ techniques uncover that the excellent MOR performance for NiW/G-light results from synergetic modulation of nickel sites by introducing tungsten and light, which provides desired adsorption behavior and high electrochemical active surface area. It’s found that introduction of W component promotes the formation of W-O-Ni(Ni3+) species, supporting more strong adsorption sites for methanol. This results in new reaction path between adsorbed methanol and OH* for producing formic acid. With application of light, the photo-generated hole promotes oxidation of residual Ni2+ into Ni3+ species, which provides additional formed NiOOH sites for MOR. It’s concluded introduction of tungsten and light is efficient for greatly enhancing methanol electrooxidation. This work is highly instructive for application of self-designed electrosynthesis method to construct dimetal/graphene composite and photoelectric synergistic catalysis towards MOR.

Cathodic luminol electrochemiluminescence on TiO2 nanotube array

This study introduces a novel fabrication of screen-printed electrode of hierarchical thin layers of TiO2 nanotube arrays (TNA) and its preliminary investigation for cathodic electrochemiluminescence (ECL) of luminol. The TNA growth on titanium foil by anodization technique was studied under various anodization times and counter electrodes (Pt wire and stainless-steel plate). Characterization using FTIR, UV-VIS DRS, and XRD revealed the increase of TiO2 formation at longer anodization times. The TNA synthesized with a stainless-steel counter electrode (TNA-SS) for 2000 s exhibited better nanotube growth and a higher electrochemical active surface area compared to the one using Pt counter electrode (TNA-Pt). The SEM characterization verified the nanotube morphology of TNA-SS with an average pore diameter of 50.46 nm and a tube length of ∼1100 nm. Notably, when TNA applied as the working electrode for the ECL of luminol, a reduction peak at −0.8 V accompanied by a clear ECL signal were observed, reaching an optimum intensity at 15 μM luminol. A comparative analysis between TNA-SS and TNA-Pt revealed the same trend of ECL signals with a significantly higher ECL intensity of TNA-SS than that of TNA-Pt. The ECL intensity of TNA-SS 2000s was also higher than TNA-SS 300s, confirming the importance of TNA surface area to the ECL activity. Nevertheless, the synthesized SPE-TNA shows great prospect to be applied in electroanalytical and sensing fields, offering opportunities for the development of electrochemiluminescence technologies.

Investigating the electrochemical performance of MnSe-supported SrZrO3 perovskite oxide nanocomposite as an electrode material for supercapacitor

Currently, the advancement in energy storage technology is a worldwide-based vital challenge, so researchers focused on the development and design of promising electrode materials for energy storage equipment. Perovskite oxide and transition metal selenide nanocomposites can achieve better cycle stability, efficient electric conductivity, high capacity, excellent redox reaction, and inattentive flexibility as electrode materials for energy storage devices and supercapacitor applications. Herein, we present the designed, fabricated, and electrochemical properties of MnSe-supported SrZrO3 nanocomposite via the Pechini method that exhibited more efficient capacitive performance than pristine SrZrO3 and MnSe. The result of electrochemical testing indicates that the SrZrO3–MnSe nanocomposite electrode possessed a battery-type pseudocapacitive nature and displayed a boosted specific capacitance of 1204 Fg-1 at a 5 mV/s scan rate in aqueous 1 M KOH solution under a three-electrode setup and maintained 95.2% retention after 3000th cycles. It also showed a higher electrochemical active surface area (1680.5 cm2), higher energy density (40 Wh/Kg), long-term cyclic stability performance, and enhanced rate capability compared to other prepared products. As a result, these findings have shown that SrZrO3–MnSe nanocomposite can be considered as potential electrode materials and might have emerging applications in commercial products for energy storage devices and supercapacitors.

Polyol-assisted synthesis of NdFeO3 nanoparticles decorated porous N-CNTs for voltammetric sensing of furazolidone in veterinary feeds and urine samples

In modern medicine, antibiotics with nitro groups were crucial for the treatment of urinary tract and bacterial infections in humans and animals. However, prolonged or excessive use of it harms the environment, humans, and animals health. Therefore, fast, accurate, and low-cost sensors have become essential for monitoring the use of drug quantities. Electrochemical methods are appropriate for determining drugs in real samples. In this work, NdFeO3 nanoparticles decorated on porous N-CNTs (NFO/N-CNTs) nanocomposite constructed through a polyol-mediated reflux heating method and explored for electrochemical applications. Various spectroscopic and analytical techniques were employed to analyze the formation of the nanocomposite. The as-synthesized NFO/N-CNTs nanocomposite possesses higher electrochemical active surface area, improved conductivity, and enhanced electrochemical activity compared to pure NdFeO3 due to the decoration of N-CNTs. The prepared nanocomposite was applied for electrochemical sensing of FZD in veterinary feeds and urine samples. The fabricated electrode NFO/N-CNTs modified glassy carbon electrode possesses a wide linear range of 0.0025–152.76 µM, a low limit of detection of 0.008 µM and a high sensitivity of 1.695 μA μM−1 cm−2 toward FZD. Furthermore, it shows significant anti-interfering ability, stability, repeatability, and reproducibility during FZD monitoring. The identification of FZD in veterinary feeds and urine samples using an NFO/N-CNTs sensor achieved acceptable results.

Accelerating photoelectrochemical CO2RR selectively of C2+ products by integrating Ag/Pd cocatalysts on Cu/Cu2O/CuO heterojunction nanorods

The Cu-based photoelectrochemical CO2 reduction reaction (PEC–CO2RR) represents a convenient approach for producing value-added C2+ products, aiming to achieve carbon neutrality by reducing greenhouse gas emissions. However, these reactions typically suffer from limited selectivity. In this work, we fabricate Cu/Cu2O/CuO nanorod (CuR)-based heterojunction architectures integrated with Ag and Pd cocatalysts to boost the selectivity of C2+ products. The proposed Cu/Cu2O/CuO/Ag-Pd (CuR/Ag-Pd) photoelectrodes are used as photocathodes to generate a maximum Faradaic efficiency (FE) of C2+ products exceeding 53% by suppressing the hydrogen evolution reaction (HER). The FE improvement is approximately 22-fold (n-propanol), 12-fold (ethanol), 13-fold (acetaldehyde), and 6-fold (acetate) compared with CuR photoelectrodes operating at a negative applied potential of −1.8 V (vs. reversible hydrogen electrode, RHE). Conversely, the CuR photoelectrodes exhibit a maximum HER rate of ∼86% at −1.8 V (vs. RHE), higher than those of the CuR/Ag (54%) and CuR/Ag-Pd (35%) photoelectrodes. The superior PEC–CO2RR performance of CuR/Ag-Pd photoelectrodes is attributable to the higher electrochemical active surface area (6.7 mF/cm2) and faster charge transfer rate at the electrode/electrolyte interface owing to the presence of cocatalysts. In addition, the CuR/Ag-Pd photoelectrodes exhibit remarkable long-term stability retaining 70% of the initial performance even after a relatively more negative applied potential at −1.2 V. A comprehensive investigation into the changes in surface morphology, crystal structure, and elemental composition after PEC–CO2RR confirms the higher stability of CuR/Ag-Pd photoelectrodes. Thus, this work provides novel perceptions into the development of Cu-based heterojunction photoelectrodes integrated with Ag/Pd cocatalysts for improving the selectivity of C2+ products.

Function‐Oriented Design of Amorphous MoS2 with Abundant Active Sites for High‐Efficiency Hydrogen Evolution Reaction

AbstractMolybdenum disulfide (MoS2) has received great interest as a highly active and cost‐effective electrocatalyst for hydrogen evolution reaction (HER). However, a main challenge for developing high‐efficiency electrocatalysts is to tailor the factors affecting the HER performance, such as composition, structure, and morphology. Herein, amorphous MoS2 electrodes with different Mo and S contents are successfully synthesized by the chemical bath deposition method using different molar ratios of Mo/S precursors (Mo/S: 4 : 1, 1 : 1 and 1 : 4) at various growth times. Experimental results indicate that the composition and the surface morphology of MoS2 are strongly sensitive to the Mo and S contents, which can create different surface roughness at the interface induced by growth times. The as‐prepared MoS2 electrode with a molar ratio of 1 : 4 exhibits superior HER activity in 1 M KOH, only requiring low overpotentials of 220 mV at 20 mA cm−2, which is much lower than those of MoS2 with a molar ratio of 1 : 1 (253 mV), and 4 : 1 (290 mV), respectively. This outstanding electrochemical performance of MoS2 (Mo/S, 1 : 4) with excellent long‐term stability can be attributed to its unique sulfur‐rich MoS2 nanosheet array structure with exposed abundant active sites, a high electrochemical active surface area (ECSA: 955.50 cm2) and superior roughness factor (RF: 3822).

Controlled synthesis of reduced graphene oxide-supported bimetallic Pt–Au nanoparticles for enhanced electrooxidation of methanol

Controlled construction of bimetallic interfaces on conductive carbon supports is extremely important for achieving better synergistic effect required for electrooxidation of small organic molecules for energy applications. Herein, controlled synthesis of reduced graphene oxide (RGO)-supported bimetallic Pt–Au nanoparticles (Pt–Au/RGO) for electrooxidation of methanol using a facile and practical approach was described. By carefully adapting sequential and simultaneous reduction steps H2PtCl6 and AuCl3were reduced on RGO support using ammonia borane (AB) and ascorbic acid (AA) as reducing agents. Three types of Pt–Au/RGO catalysts were prepared and labeled as PtAu/RGO-AB1, PtAu/RGO-AB, and PtAu/RGO-AA. The reduction process was carried at ambient conditions, without the use of surfactants, and the catalysts obtained were analyzed through various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS). The PtAu/RGO-AB1 catalyst showed remarkable uniformity on the RGO sheets, with an average particle size of 2–3 nm. The electrochemical behavior of Pt–Au catalysts supported on reduced graphene oxide (RGO) for methanol oxidation was systematically investigated via cyclic voltammetry and chronoamperometry techniques. Among the studied catalysts, PtAu/RGO-AB1 exhibited high electrochemical active surface area (ECSA) of 92.47 m2/g, along with the highest mass and ECSA-normalized activities for the electrooxidation of methanol. PtAu/RGO-AB1 manifested exceptional resistance to accumulated CO-like species, as evidenced by its higher forward peak current density to reverse peak current density ratio (If/Ib) of 2.20. The facile and effective synthesis strategy described here provides a promising method for fabricating well-defined multi-component nanostructured electrocatalysts with potential applications for various fuel cell reactions.

Efficient electrochemical hydrogen evolution activity of nanostructured Ag3PO4/MoS2 heterogeneous composite catalyst

Hydrogen (H2) generation by electrochemical water splitting is a key technique for sustainable energy applications. Two-dimensional (2D) transition-metal dichalcogenide (MoS2) and silver phosphate (Ag3PO4) possess excellent electrochemical hydrogen evolution reaction (HER) properties when they are combined together as a composite rather than individuals. Reports examining the HER activity by using Ag3PO4, especially, in combination with the 2D layered MoS2 are limited in literature. The weight fraction of MoS2 in Ag3PO4 is optimized for 1, 3, and 5 wt%. The Ag3PO4/1 wt % MoS2 combination exhibits enhanced HER activity with least overpotential of 235 mV among the other samples in the acidic medium. The synergistic effect of optimal nano-scale 2D layered MoS2 structure and Ag3PO4 is essential for creating higher electrochemical active surface area of 217 mF/cm2, and hence this leads to faster reaction kinetics in the HER. This work suggests the advantages of Ag3PO4/1 wt % MoS2 heterogeneous composite catalyst for electrochemical analysis and HER indicating lower resistivity and low Tafel slope value (179 mV/dec) among the prepared catalysts making it a promising candidate for its use in practical energy applications.

(Invited) Enhancement of Activity of Low-Pt-Content-Catalysts Toward Oxygen Reduction through Admixing with Metal Oxide Cocatalysts

The proton-exchange membrane fuel cell (PEMFC) technology is one of the most promising approaches for energy conversion in automotive applications. Despite the use of expensive noble metal electrocatalysts, the sluggish kinetics of the oxygen reduction reaction (ORR) in acid media, and formation of the undesirable hydrogen peroxide intermediate are still the main drawbacks, on top of the stability problems, when it comes to the widespread commercialization of PEMFC devices. The progress in this subject is greatly hindered by the high cost and scarcity of the state-of-the-art platinum-based materials which are regarded as the most effective cathode catalysts. Therefore, most of the current research studies have been devoted to the optimization of active centers and maximization of their utilization, which should allow the lowering of the cathode Pt loadings without loss of performance and durability. Unfortunately, the problem of electrochemical stability and the danger of generation of higher quantities of the undesirable hydrogen peroxide intermediate may become even more serious in the case of systems utilizing lower amounts of the Pt catalystAmong important strategies is hybridization, activation, and stabilization of carbon-supported Pt catalysts by functionalization through admixing with certain nanostructured and typically substoichiometric metal oxides. Special attention is paid to application of the bi- or multi-metallic Pt-based alloys in their various forms and structures. Additionally, doping of carbon carriers with heteroatoms would produce surface functional groups and active centers capable of not only improving the catalysts’ performance, but also affecting their stability. Among other important issues are such features as porosity, hydrophilicity, and degree of graphitization of carbon components, in addition to the existence of metal–support interactions, high electrochemical active surface area, electronic structure of interfacial Pt, and the feasibility of adsorptive or activating interactions with oxygen molecules.Platinum is a main catalyst for the electroreduction of oxygen, the reaction of primary importance to the technology of low-temperature fuel cells. Because of high cost of platinum. there is a need to significantly lower its loadings at interfaces. But then O2-reduction proceeds often at less positive potentials and produces higher amounts of undesirable H2O2-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO2, WO3, Ta2O5, Nb2O5, ZrO2), stabilize Pt and carbon nanostructures, diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction of oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. The catalytic efficiency depends on geometric (decrease of Pt–Pt bond distances) and electronic (increase of d-electron vacancy in Pt) factors, in addition to possible metal-support interactions and interfacial structural changes affecting adsorption and activation of O2-molecule.

(Invited) Unravelling the Core of Fuel Cell Performance: Engineering the Electrolyte (ionomer)/Catalyst Interface

The biggest challenge of the widespread implantation of the polymer electrolyte membrane fuel cells (PEMFCs) is the cost, primarily due to the use of platinum catalysts. The high intrinsic catalyst activity exhibited using a rotating disc electrode (RDE) is rarely realized in the membrane electrode assembly (MEA), which is the core of PEMFC, due to the difference on the electrolyte(ionomer)/catalyst interfaces. To translate the catalyst RDE performance into MEA, the design of an ideal ionomer/catalyst interface is proposed: a thin, conformal ionomer film covers the maximum surface of a Pt nanoparticle that simultaneously maximizes catalyst utilization, (i.e. high mass activity and electrochemical active surface area) and O2 diffusion (i.e. high current density performance) without compromising proton conduction. Building such an interface is a long-standing challenge due to no control of ionomer distribution over catalyst particle, resulting in large ionomer agglomerates and inhomogeneous ionomer coverage over the catalyst nanoparticle, consequently, poor fuel cell performance. In this work, this ionomer/catalyst interface has been constructed utilizing the electrostatic charge attraction between positively charged catalyst and negatively charged ionomer particles in a liquid and preserved into a solid catalyst layer. Consequently, this interface leads to the previously unachieved fuel cell performance on both the catalyst utilization (75% vs. 45%) and the rated/peak power density (Pt/C, 0.910/1.430 W/cm2 for H2/Air, Pt loading: 0.1 mgPt/cm2), matching that of Pt alloy catalysts. This work demonstrated the formation of the interface in the liquid phase (using ultra-small angle x-ray scattering in combination with cryo-TEM, isothermal‐titration‐calorimetry) and the preserved interface in the solid catalyst layer (using TEM) and estimated the effective coverage and thickness of the ionomer film (using the limiting current density, RDE and fuel cell performance).

Manufacturing Strategies for Engineering Carbon Electrodes Via Non-Solvent Induced Phase Separation

Porous electrodes are at the core of emerging electrochemical systems and tuning the electrode properties is critical to overcome system-specific limitations. To meet the stringent performance and cost requirements, there is a need for tailored microstructures generated through inexpensive and scalable synthesis methods with precursors originating from reliably-sourced, globally-abundant feedstocks. To this end, we recently introduced a manufacturing route using non-solvent induced phase separation (NIPS), yielding porous carbon electrodes with multimodal and interconnected porosity. The synthesized NIPS electrodes demonstrated a beneficial trade-off between transport properties (permeability, mass transfer) and electrochemically active surface area (ECSA) resulting in high performance in iron and all-vanadium redox flow batteries (RFBs)[1,2]. Moreover, NIPS manufacturing offered control over electrode characteristics (pore size, surface area) which are critical parameters for broader electrochemical devices. Besides its use for RFB application, we hypothesize that the electrode morphologies resulting from NIPS could be applied to a broader range of electrochemical systems employing porous electrodes. Consequently, here we focus on extending the library of electrode microstructures achievable via NIPS through the alteration of simple process parameters.In this presentation, I will discuss our latest advances on the bottom-up manufacturing of porous electrodes using NIPS targeting porosity gradients and high ECSA materials. For the former, we introduce the use of a control layer, casted on top of the NIPS polymer solution at the interface with the coagulation bath, thereby altering the rate of the phase separation process. We investigate various process parameters such as the composition, viscosity, and thickness of the control layer and assess their effect onto the resulting microstructures. The NIPS method assisted by a control layer generates porosity gradients, resulting in a slight increase of the electrode ECSA at the cost of a higher pressure drop. To further increase the ECSA of the prepared electrodes, we also propose nano-patterning approaches to significantly enhance ECSA through addition of nano-scale porosity without compromising the pressure drop through the porous structure. Finally, both porosity gradient and nano-patterned NIPS electrodes are tested in a all-vanadium redox flow cell to extract microstructure-performance relationships. Despite being in its early technological stage, this work illustrates the versatility of NIPS to manufacture porous electrodes through a very broad microstructural design space.

ORR Activity and Voltage-Cycling Stability of a Carbon-Supported PtxY Alloy Catalyst Evaluated in a PEM Fuel Cell

Platinum-yttrium alloys (PtxY) are suggested to have superior oxygen reduction reaction (ORR) activity and long-term stability in proton exchange membrane fuel cells (PEMFCs). However, the actual ORR activity and stability of a PtxY catalyst with a high electrochemically active surface area (ECSA) in a PEMFC remains uncertain. Here, a Ketjen black (KB) carbon supported PtxY/KB catalyst with a high ECSA (∼60 m2/g) was synthesized using a carbon nitride precursor. Based on elemental analysis, XRD, electron microscopy, and a mass-balance based model, it was shown that the acid-leached PtxY nanoparticles of the catalyst consist of a ∼0.7 nm thick Pt-shell and a Pt3Y core. Rotating disk electrode (RDE) and 5 cm2 single-cell PEMFC measurements indicated that the ORR activity of the acid-leached PtxY/KB catalyst is similar to an analogously synthesized Pt/KB reference catalyst with the same ECSA. Voltage-cycling accelerated stress tests (ASTs) between 0.6−1.0 V (in H2/N2 at 80 °C/95% RH) in 5 cm2 single-cells showed that the ORR activity and durability of the PtxY/KB catalyst is similar to that of the Pt/KB reference catalyst. Thus, the high durability of Pt-rare Earth alloys that has been claimed on the basis of RDE measurements is not observed in actual PEMFCs.

Ultra-fine Fe3C nanoparticles decorated in the Fe–N co-doped carbon networks with hierarchical nanoarchitectonics towards efficient oxygen reduction electrocatalysis

The iron-nitrogen co-doped carbon (Fe–N–C) materials have considered one of the oxygen reduction reaction catalysts with the best potential. Unfortunately, their insufficient intrinsic activity and low active sites result in thick cathode catalytic layers of fuel cell, which has limited discharge performance of the Fe–N–C catalysts in the fuel cells. Herein, a supramolecular assembly strategy is designed to prepare accessible Fe-Nx sites and ultra-fine Fe3C nanoparticles in porous carbon nanosheet with optimized pore structure toward oxygen reduction electrocatalysis. It is found that supramolecular assembly strategy has significantly increased the specific surface area and Fe-Nx site content, and induced the formation of highly dispersed Fe3C nanoparticles, which contributes to the high electrochemical active surface area and catalytic activity. The obtained FeNC-900-S catalyst exhibits a high half-wave potential of 0.860 V and a current density of up to 8.28 mA/cm2 (Jk at 0.85 V) in 0.1 M KOH, outperforming the those of commercial Pt/C. More importantly, when the FeNC-900-S is employed as an air cathode catalyst towards zinc-air batteries, it obtains an open-circuit voltage of 1.548 V, a power density of 188.8 mW/cm2 and a specific capacity of 790.5 mAh/g.

Influence of boron doping level and calcination temperature on hydrogen evolution reaction in acid medium of metal-free graphene aerogels

In this work, metal-free boron-doped graphene-based aerogels were successfully synthesized via a one-step autoclave assembly followed by freeze-drying and used as electrocatalysts for the hydrogen evolution reaction (HER) in acidic media. The synthesized reduced graphene oxide aerogels (rGOA) showed improved electrocatalytic activity by introducing boron and structural defects. The amount of boric acid used both as a dopant and reducing agent in the synthesis was optimized (boric acid/GO mass ratio = 17.5) to practically reach the crystallization limit of boric acid (boric acid/GO mass ratio = 20). It was observed that the higher the amount of boric acid added, the more boron was incorporated into the carbonaceous structure, improving the electrocatalytic activity of the final aerogel. Furthermore, calcination of the boron-doped electrocatalyst at 600 °C resulted in final aerogels with low oxygen content, moderate surface area, bimodal pore size distribution, and a high electrochemical active surface area. The final 3D graphene aerogel developed in this work, showed such outstanding electrocatalytic activity in HER as to replace noble metal-based electrocatalysts in the future.

Layer interfacing strategy to derive free standing CoFe@PANI bifunctional electrocatalyst towards oxygen evolution reaction and methanol oxidation reaction

Developing inexpensive, highly electrochemically active, and stable catalysts towards electrochemical studies remains challenge for researchers. In this regard, binder-free CoFe@PANI composite electrocatalyst is deposited on nickel foam (NF) substrate via successive electrodeposition of polyaniline (PANI) and CoFe-LDH at Room temperature (RT). As deposited binder-free CoFe@PANI electrocatalyst displays high electrocatalytic activity towards oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) in alkaline media. In CoFe@PANI structure, interfacing of high-electron conducting PANI establishes strong interconnection with CoFe-LDH by tuning electronic structures, which accelerates the electrochemical performance towards OER and MOR. For OER, CoFe@PANI requires low overpotential (η10) of 237 mV to reach current density (Id) of 10 mA cm−2 and displays low Tafel slope value of 46 mV dec−1 in 1 M KOH solution. Also, it displayed specific Id of 120 mA cm−2, when it was tested for MOR in 1 M KOH with 0.5 M methanol solution. The superior electrocatalytic activity of CoFe@PANI is mainly ascribed to high electrochemical active surface area (ECSA), abundant active sites and fast electron transfer between electrocatalyst and electrode surface. Of note, the current work may open new era for design and development of non-precious highly active and stable hybrid electrocatalysts at RT for various applications.