High Electrochemical Surface Area Research Articles

One‐Step Synthesis of Phase‐Controlled Co2P Nanoparticles as an Electrocatalyst for Hydrogen Evolution Reaction

AbstractCobalt phosphides have been investigated as potentially useful electrocatalysts for accelerating hydrogen evolution. Cobalt phosphide electrocatalysts are synthesized in a single step at varied phosphating temperatures (350, 400, 450 °C) via the gas phase approach. Synthesized at a phosphating temperature of 350 °C, Co2P (CP‐350) transforms into a mixed phase that contains both Co2P and CoP (CP‐400 and CP‐450) as the phosphating temperature goes up which is confirmed by XRD. CP‐350, CP‐400, and CP‐450 exhibited overpotentials of 181, 270, and 293 mV respectively with Tafel slopes of 112, 146, and 175 mV/dec. In contrast to CP‐400 and CP‐450, CP‐350 revealed superior hydrogen evolution reaction (HER) performance and stability for up to 12 h due to its pure phase (Co2P), high surface area (151 m2/g), and high electrochemical surface area (7.02 cm2) with low charge transfer resistance. According to our work, changing the phase and active surface area of transition metal phosphide catalysts can greatly increase their HER catalytic efficiency.

Highly Selective Electroreduction of Nitrobenzene to Aniline by Co-Doped 1T-MoS2.

The selective electrocatalytic reduction of nitrobenzene (NB) to aniline demands a desirable cathodic catalyst to overcome the challenges of the competing hydrogen evolution reaction (HER), a higher overpotential, and a lower selectivity. Here, we deposit Co-doped 1T MoS2 on Ti mesh by the solvothermal method with different doping percentages of Co as x % Co-MoS2 (where x = 3, 5, 8, 10, and 12%). Because of the lowest overpotential, lower charge-transfer resistance, strong suppression of the competing HER, and higher electrochemical surface area, 8% Co-MoS2 achieves 94% selectivity of aniline with 54% faradaic efficiency. The reduction process follows first-order dynamics with a reaction coefficient of 0.5 h-1. Besides, 8% Co-MoS2 is highly stable and retains 81% selectivity even after 8 cycles. Mechanistic studies showed that the selective and exothermic adsorption of the nitro group at x % Co-MoS2 leads to a higher rate of NB reduction and higher selectivity of aniline. The aniline product is successfully removed from the solution by polymerization at FTO. This study signifies the impact of doping metal atoms in tuning the electronic arrangement of 1T-MoS2 for the facilitation of organic transformations.

Study on oxygen evolution reaction efficiency demonstrated by Ce-E (E = S, Se and te) electrocatalyst

The strategy of generating sustainable energy with hydrogen fuel is highly significant and promising. Hydrogen fuel being non-toxic proves beneficial for the environment and can be produced in a variety of ways, as industrial water splitting into oxygen and hydrogen is a crucial future plan. This study aims to investigate cerium-based chalcogens (CeS, CeSe, and CeTe), as a catalyst to broaden the family of highly effective OER electrocatalysts based on transition metal chalcogenides. CeTe on NF was found to exhibit lowest onset potential with an overpotential of 333 mV at 10 mAcm−2 and a 51 mVdec−1 Tafel value among CeE (E = S, Se) chalcogenides with comparable stoichiometry. Using different analyses, it was determined that CeTe had a large surface area of 83.7 m2g-1, a cubic structure, and a highly crystalline nanoflakes morphology. High electrochemical surface area of 562 cm2, small resistance as Rs of 1.12 Ω, and Rct 729 mΩ, along with high TOF value of 0.174 s−1, 0.059 s−1, 0.009 s−1 for CeTe as compared to CeSe and CeS have supported by CV results. In particular, CeTe showed exceptional catalytic efficiency and was highly active and durable in oxygen evolution reactions.

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.

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.

Lutetium-Induced Ultrafine PtRu Nanoclusters with a High Electrochemical Surface Area for Direct Methanol Fuel Cells at Alleviated Temperatures.

PtRu alloys have been recognized as the state-of-the-art catalysts for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, their applications in DMFCs are still less efficient in terms of both catalytic activity and durability. Rare earth (RE) metals have been recognized as attractive elements to tune the catalytic activity, while it is still a world-class challenge to synthesize well-dispersed Pt-RE alloys. Herein, we developed a novel hydrogen-assisted magnesiothermic reduction strategy to prepare a highly dispersed carbon-supported lutetium-doped PtRu catalyst with ultrafine nanoclusters and atomically dispersed Ru sites. The PtRuLu catalyst shows an outstanding high electrochemical surface area (ECSA) of 239.0 m2 gPt-1 and delivers an optimized MOR mass activity and specific activity of 632.5 mA mgPt-1 and 26 A cmPt-2 at 0.4 V vs saturated calomel electrode (SCE), which are 3.6 and 3.5 times of commercial PtRu-JM and an order higher than PtLu, respectively. These novel catalysts have been demonstrated in a high-temperature direct methanol fuel cell running in a temperature range of 180-240 °C, achieving a maximum power density of 314.3 mW cm-2. The AC-STEM imaging, in situ ATR-IR spectroscopy, and DFT calculations disclose that the high performance is resulted from the highly dispersed PtRuLu nanoclusters and the synergistic effect of the atomically dispersed Ru sites with PtRuLu nanoclusters, which significantly reduces the CO* intermediates coverage due to the promoted water activation to form the OH* to facilitate the CO* removal.

Strong electric field at the sharp tips of Cu(OH)2 nanochrysanthemums for selective electrochemical CO2 conversion into ethylene

Electrochemical CO2 reduction reaction (CO2RR) is an attractive approach for the mitigation of CO2 emissions and the production of value-added chemicals. However, it remains a challenge to achieve high selectivity of desirable C2 products like ethylene (C2H4) with high economic value and large market. Herein, we report the fabrication of unprecedented Cu(OH)2 nanochrysanthemums catalyst layer (CL). Interestingly, Cu(OH)2 nanochrysanthemums CL exhibits a C2H4 Faradaic efficiency (FE) of 51.2 ± 0.5% and a FE(C2H4+C2H5OH) of 70.0 ± 0.5% in pH nearly neutral electrolytes. It is worth mentioning that Cu(OH)2 nanochrysanthemums CL achieves the highest FEC2 among documented Cu(OH)2 electrocatalysts. The high FEC2H4 and FEC2 can be attributed to the high electrochemical surface area (ECSA, 21.9 mF/cm2) of Cu(OH)2 nanochrysanthemums. In addition, the wellbalanced hydrophilicity-hydrophobicity of the Cu(OH)2 nanochrysanthemums CL also contributes to the high FEC2H4 and FEC2 by simultaneously satisfying efficient transfer of hydrophobic CO2 and C2H4 as well as hydrophilic H2O and C2H5OH. COMSOL multiphysics simulations and density functional theory (DFT) calculations further suggest that the negatively charged sharp tips of Cu(OH)2 nanochrysanthemums would trigger the accumulation of K+ and offer strong local electric field of 9.8 V/μm, promoting C–C coupling and suppressing hydrogen evolution reaction (HER).

Hierarchical Sea Urchin-like Fe-doped Heazlewoodite for High-Efficient Oxygen Evolution.

Electrochemical water-splitting to produce hydrogen is potential to substitute the traditional industrial coal gasification, but the oxygen evolution kinetics at the anode remains sluggish. In this paper, sea urchin-like Fe doped Ni3S2 catalyst growing on nickel foam (NF) substrate is constructed via a simple two-step strategy, including surface iron activation and post sulfuration process. The NF-Fe-Ni3S2 obtains at temperature of 130 °C (NF-Fe-Ni3S2-130) features nanoneedle-like arrays which are vertically grown on the particles to form sea urchin-like morphology, features high electrochemical surface area. As oxygen evolution catalyst, NF-Fe-Ni3S2-130 exhibits excellent oxygen evolution activities, fast reaction kinetics, and superior reaction stability. The excellent OER performance of sea urchin-like NF-Fe-Ni3S2-130 is mainly ascribed to the high-vertically dispersive of nanoneedles and the existing Fe dopants, which obviously improved the reaction kinetics and the intrinsic catalytic properties. The simple preparation strategy is conducive to establish high-electrochemical-interface catalysts, which shows great potential in renewable energy conversion.

Well-defined ternary metal phosphide nanowires with stabilized Pt nanoclusters to boost alkaline hydrogen evolution reaction

Designing low-content and high-activity Pt-based catalysts with the high durability for the electrochemical hydrogen production remains a challenge. In this study, a ternary metal phosphide (NiCoP) with 1D nanowire (NW) and 2D nanosheet (NS) morphologies incorporating Pt clusters (denoted as Ptcluster-NiCoP@NF NWs and Ptcluster-NiCoP@NF NSs, respectively) was prepared using a hydrothermal–phosphorization–electrodeposition method. Based on the “tip effect” of NWs and a high electrochemical surface area, the as-prepared Ptcluster-NiCoP@NF NWs display better hydrogen evolution reaction (HER) performance, with a low overpotential of 65 mV at a high current density of 100 mA cm−2 and a low Tafel slope of 38.86 mV dec−1, than the Ptcluster-NiCoP@NF NSs, with an overportential of 95 mV at 42.53 mV dec−1. This indicates that the NiCoP NW-based support exhibits faster HER kinetics. The mass activity (11.47 A mgPt−1) of the Ptcluster-NiCoP@NF NWs is higher than that of commercial Pt/C catalysts. Significantly, the Ptcluster-NiCoP@NF NWs display excellent cyclic stability with negligible losses for 5000 cycles and 30-h tests at a high current of 500 mA cm−2.

Activity and stability of electrochemically reduced graphene oxide films for applications requiring mixed conductivity

A protonic and electronic conductor composed of partially reduced graphene oxide (GO) has been prepared by electrochemical methods. Conductivity measurements and detailed surface analysis by XPS, FTIR, and Raman methods show that the electrochemically reduced GO (ERGO), prepared under different reduction potentials, exhibits a unique dual (protonic and electronic) conductivity which is tunable by adjusting the surface conditions. Selected removal of the oxygenated groups, evolution of C(sp2)/C(sp3) hybrid carbon structure, and surface structure of ERGO can impact the protonic and electronic transport mechanisms. The ERGO samples reported here are ideal support materials with proper ratios of protonic and electronic transport. The as-prepared ionomer-free and flexible ERGO-supported Pt (Pt/ERGO) electrodes were characterized for oxygen reduction reaction (ORR) reactivity in acidic solution. The results showed not only higher electrochemical surface area (ECSA), but also improved mass activity towards ORR compared to conventional carbon supported Pt catalysts.

New approach to produce cubic-WC at low temperature for hydrogen evolution reaction

A novel catalyst, a nanostructured cubic-WC (c-WC) flat film, is introduced for the hydrogen evolution reaction (HER) using a specialized magnetron sputtering system. This method results in over 94% crystalline c-WC0.95 formation at room temperature, featuring high-density stacking faults and twin defects. The catalytic performance of the c-WC film for HER is investigated through theoretical simulations and experimental studies. Density-functional theory (DFT) suggests that the c-WC (100) surface exhibits faster reaction kinetics than c-WC (111) surface, approaching the efficiency of Pt (111) surfaces. Experimentally, the c-WC0.95 film exhibits a high electrochemical surface area and increased active sites due to surface defects. Differential electrochemical mass spectrometry (DEMS) confirms an onset potential for HER of −50.0 mV for c-WC0.95 films and establishes electrodesorption as the rate-determining step. Overall, the c-WC film emerges as a cost-effective and efficient catalyst for green hydrogen production, showcasing excellent reproducibility and electrochemical stability.

Synthesis of Ni-Doped Graphene Aerogels for Electrochemical Applications.

Carbonaceous materials used in most electrochemical applications require high specific surface area, adequate pore size distribution, and high electrical conductivity to ensure good interaction with the electrolyte and fast electron transport. The development of transition metal doped graphene aerogels is a possible solution, since their structure, morphology, and electrical properties can be controlled during the synthesis process. This work aims to synthesize Ni-doped graphene aerogels to study the role of different nickel salts in the sol-gel reaction and their final properties. The characterization data show that, regardless of the nature of the Ni salts, the surface area, volume of micropores, and enveloped density decrease, while the porosity and electrical conductivity increase. However, differences in morphology, mesopore size distribution, degree of order of the carbon structure, and electrical conductivity were observed depending on the type of Ni salt. It was found that nickel nitrate results in a material with a broader mesopore distribution, higher electrical conductivity, and hence, higher electrochemical surface area, demonstrating that graphene aerogels can be easily synthesized with tailored properties to fit the requirements of specific electrochemical applications.

VOx@ graphene electro-catalysts for water splitting and dopamine sensing

Vanadium oxide@graphene (VOG) composites were synthesized using facile hydrothermal method by varying the synthesis time from 6 to 24 h. The samples with best catalytic characteristics were reprepared by replacing graphene oxide with N-doped graphene in the initial hydrothermal reaction. The role of graphene/N-doped graphene in determining the catalytic properties of vanadium oxide was effectively studied using various characterizations viz. X-ray diffraction, Fourier Transform Infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Maximum hydrogen evolution reaction (HER) activity with high current density of –31.07 mA/cm2 (Tafel slope = 162 mVdec−1) has been achieved for VONG-24 sample, indicating Volmer reaction as rate determining step. The high electrochemical surface area (ECSA) of VOG-24 sample in 1 M KOH corroborated the enhanced current density of 144.90 mA/cm2 (Tafel slope = 83 mVdec−1) for maximum oxygen evolution reaction (OER) activity. The VOG12/GCE sample with a 0.29 μM limit of detection (LOD) proved to be the best electrochemical sensor for dopamine (DA) in a wide linear detection range i.e., 1–150 μM. Both catalytic as well as sensor responses of VOG samples were deeply influenced by the amount of O-species along with relative ratios of the V3+, V4+ and V5+. The nature of the graphene in the initial mixture emerged as a crucial parameter in tailoring the vanadium valence state content in the composites.

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.

Detection of vanillin in food products over Cu - laser induced graphene nanocomposite using the combined electrochemistry and UV–Vis spectroscopy principles

Vanillin is the fragrant phenolic compound widely used as a food additive. However, an excessive consumption of vanillin can have adverse effects on human health. Therefore, the development of a sensor for the rapid and precise measurement of vanillin is essential. In this study, vanillin is successfully measured using the UV–Vis spectroelectrochemical (SEC) method. The method uses the laser induced graphene (LIG)-supported Cu nanoparticles coated over an indium tin oxide (ITO) as the electrode. The precursor material for Cu-LIG is synthesized using the suspension polymerization of phenol and formaldehyde, with the in-situ inclusion of Cu during gel formation step. The resulting polymeric film is subjected to calcination, hydrogen-reduction, and laser ablation to create a conductive Cu-LIG layer. The synthesized material exhibits a high electrochemical surface area of 0.907 cm2/cm2 and electrical conductance of 0.002 S, rendering it a suitable electrocatalyst for the oxidation of vanillin. The Cu-LIG/ITO electrode is used in detecting the oxidized species of vanillin at 370 nm-wavelength post two cyclic voltammetry (CV) cycles over 0–1.3 V potential. The sensor shows an excellent linear response (R2 value ∼ 0.993) over the concentration range 0.25–40 μg/mL, with 0.14 μg/mL limit of detection. Owing to the anti-interference ability of the SEC sensor, the intensity of UV–Vis absorbance at 370 nm remains unaffected against common interferents including glucose, fructose, ascorbic acid, and uric acid found in real food substances. This study has clearly shown the advantages of the combined electrochemistry and UV–Vis spectroscopy principles in quantitatively detecting oxidizable compounds in commercial food products.

Influence of Ethanol Decomposition on Dispersion of PEFC Catalyst Ink

To achieve high power density operation of polymer electrolyte fuel cells (PEFCs), it is required to realize high-performance catalyst layer with low oxygen transport resistance, high proton and electron conductivities, and high electrochemical surface area (ECSA) with low Platinum loading. Because dispersion structure of catalyst ink strongly affects porous structure of the catalyst layer, it is crucial for realization of high-performance catalyst layer to understand the dispersion mechanism of the catalyst ink. Our group has reported that decomposition of ethanol, as a solvent, by platinum catalyst significantly affects aggregation of the catalyst ink. [1, 2] But, the mechanism of the catalyst ink aggregation was not fully understood. In this study, effect of ethanol decomposition on the aggregation of the catalyst ink was investigated.The catalyst ink was fabricated by mixing platinum-supported carbon (TEC10V30E, Tanaka Kikinzoku), ionomer (DE1021, Sigma-Aldrich), and water/ethanol solvent (water/ethanol: 60/40 wt%). Decomposition product of ethanol within the catalyst ink solvent was analyzed by GC/MS (GCMS-QP2020NX, SHIMADZU), and presence of acetaldehyde (C2H4O) and acetic acid (CH3COOH) was detected. In order to investigate the influence of these products on aggregation of the catalyst ink, acetaldehyde or acetic acid was added to the catalyst ink. The particle size distribution was evaluated by using laser diffraction type particle size distribution meter (LA-960V2, HORIBA) without dilution, and it was confirmed that the acetaldehyde-added catalyst ink showed larger particle size and the acetaldehyde caused the aggregation of the catalyst ink (Figure 1). In addition, dispersion of the catalyst ink was observed by using an optical microscopy, and aggregation of the catalyst ink by adding the acetaldehyde was clearly observed (Figure 2). To understand the aggregation mechanism by adding acetaldehyde, ionomer adsorption fraction on the platinum-supported carbon was measured by using centrifugation method, and the decrease in ionomer adsorption fraction by adding acetaldehyde was confirmed. From these results, it was confirmed that acetaldehyde generated by the decomposition of ethanol in the catalyst ink leads to a decrease in the ionomer adsorption fraction. It is reported that the ionomer promotes the dispersion of platinum-supported carbon due to electrostatic repulsion forces, and it is suggested that the decrease in ionomer adsorption fraction results in the aggregation of the catalyst ink. Therefore, to realize high-performance catalyst layer, influence of acetaldehyde should be minimized and further research is requested to understand it. Acknowledgement This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Rational Design of Fe-Based Layered Double Hydroxide for Water Oxidation: Molecular and Cationic Engineering

Nowadays, in the field of electrocatalysts for the oxygen evolution reaction, Fe-based LDHs stand out as one of the best oxygen evolution reactions (OER) electrocatalysts in alkaline conditions. In the attempt to improve the electrochemical performance of Fe-LDHs-based electrodes, many approaches have been reported.[1] Beyond these, interlayer space, Fe-clustering and covalent functionalization have been not explored, being the last two synthetic challenges within the field of LDHs.On the one hand, to explore the influence of interlayer space in the behaviour of Fe–LDHs as an oxygen evolution reaction (OER) electrocatalyst, we develop a family of NiFe-LDHs with the same metal composition, morphology, and dimensions and different alkyl sulfate to reach extreme ranges of basal spacing (from 8 to 32 Å). Increasing the basal space of the LDH results in a higher electrochemical surface area and a reduction of the resistance related to the chemisorption of oxygen leading to better kinetic behaviour. Indeed, the Tafel slope for the NiFe–LDHs with the highest basal space studied is similar to that obtained for exfoliated NiFe nanosheets and shows better stability as a consequence of the tridimensional robustness of the hybrid material.[2]On the other hand, to shed light on the influence of Fe-clustering on the OER performance, firstly, we have selected MgFe-based LDHs phases as model systems. By optimization of a hydrothermal method based on triethanolamine different Fe-clustering degree has been achieved, and thanks to the diamagnetic behaviour of Mg, a simple magnetic characterisation allows us to identify the Fe-clustering degree. Nevertheless, both samples behave identically in terms of OER performance when glassy carbon electrodes are used. Surprisingly, striking differences arise when the samples are tested on nickel foam. Specifically, the sample exhibiting the lower Fe-clustering behaves as a better electrocatalyst with a reduction of the overpotential values of more than 50 mV to reach 100 mA/cm2, as a consequence of a favoured surface transformation of MgFe-LDHs phases into more reactive oxyhydroxide NiFe-based ones during the electrochemical tests. [3] To extend our study to NiFe-LDH, we have successfully synthesized high-clustering nanometric NiFe-LDHs using a scalable synthesis approach. This synthetic protocol has allowed us to obtain a significantly higher concentration of approximately 100 g/L of our materials, which is almost two orders of magnitude larger than current state-of-the-art synthetic methods. Importantly, the Fe-clustering of this scale-up NiFe-LDH results in improved electrochemical performance compared to traditionally synthesized NiFe-LDH/FeOOH across various current density ranges and different electrochemical setups, including rotatory disk electrode (RDE) and Anion Exchange Membrane Water Electrolyzer (AEMWE), with testing conducted up to a current density of 3 A·cm-2. For instance, the overpotential at 2.5 A·cm-2 for the scale-up NiFe-LDHs is measured at 1.96 V, whereas the traditionally synthesized NiFe-LDH/FeOOH exhibit a higher overpotential of 2.18 V. [4]Last but not least, the covalent functionalization of LDHs has been explored to enhance their processability and stability as an electrocatalyst, for this, we develop for the first time the covalent functionalization of Fe-LDHs beyond silane-based molecules due to the reversible character of this bond in alkaline media. By a modified hydrothermal method from Kuroda et al. [5], the covalent functionalization of NiFe-LDHs with tris(hydroxymethyl) aminomethane (Tris) was performed. The NiFe-Tris LDH were fully characterized to identify the structural differences with a bare LDH. At the same time, the stability of the covalent functionalization in basic media was proved. Interestingly, the Tris molecule anchored to LDHs increases the electrocatalytic stability in absence of binder material. Thus, after 40 hours of the OER, the overpotential increase is 37% lower in the NiFe@Tris than in the NiFe-Cl@bare. To check the origin of this overpotential decrease, ICP analysis of electrolytes pre-treated with acid after the stability test was performed. A reduction of 27% and 17% of Ni and Fe respectively is observed in the electrolyte for functionalized samples. Consequently, it is demonstrated that, regardless of the decomposition process (detachment or dissolution), the NiFe-LDH functionalized presents greater stability.[6]Overall, we demonstrated that the rational design of LDHs can enhance catalytic activity and stability for their use as electrocatalysts for the oxygen evolution reaction.

Transition Metal (Ni/Cu) Based Bimetallic Catalyst for Glycerol Oxidation

Alcohol fuel cell is considered as one of the most promising green energy generation option. Glycerol can be used as a potent fuel because of its excellent energy density, ready availability, financial viability and minimal toxicity. Moreover, glycerol is also an active petroleum by-product. In direct glycerol fuel cell, precious noble metal based catalyst was extensively used as electro-catalyst for glycerol oxidation. The use of noble metal as catalysts restricted the viable commercialisation due to its high cost. This study intended to use transition metal such as nickel and copper based monometallic and bimetallic catalyst for glycerol oxidation to lower down the cost of commercialisation. These metals already proved to be efficient catalyst for electro-oxidation of methanol and ethanol [1-2]. Carbon was already proved to prominent support material for electro-catalyst due to high surface area and superior conductivity.The metals were impregnated into carbon support followed by reduction under H2/Ar environment with 20 wt % metal loading. The weight ratio of Ni and Cu in bimetallic catalyst was fixed as 1:1. The average metal particle size of the catalysts varied between 7.8 to 16.3 nm. The cyclic voltammetry of different catalysts for 0.5 M glycerol oxidation in 1 M KOH is shown in Fig 1a). The onset potential of bimetallic catalyst (NiCu/C) was reduced to 0.20 V compared to their monometallic counterpart (0.39 V for Ni/C and 0.42 for Cu/C). The glycerol oxidation peak was observed at 0.71, 0.73 and 0.78 V for Cu/C, Ni/C and NiCu/C respectively. The specific activity and mass activity was shown in Fig 1b). The highest specific (76 mA/cm2) and mass activity (775 mA/mgmetal) was obtained for NiCu/C from glycerol oxidation. The obtained electrochemical surface area (ECSA) was highest for NiCu/C (99 m2/g) followed by Ni/C (44 m2/g) and Cu/C (34 m2/g). The higher activity of NiCu/C could be attributed to the lower Tafel slope, higher ECSA and charge transfer co-efficient. The EIS results conveyed that electro-oxidation process was slower than charge transfer process. Moreover, lowest time constants for the both the process was observed for NiCu/C catalyst. Hence, NiCu/C proved to be efficient electro-catalyst with superior activity for glycerol oxidation in direct glycerol fuel cell. Fig 1. a) Cyclic voltammetry of different catalyst in 0.5 M glycerol and 0.1 M KOH and b) Specific and mass activity of different catalyst.

(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).