Apparent Electrocatalytic Activity Research Articles

IrO2-ZrO2-SiO2 ternary oxide composites- based DSAs: Activity toward oxygen evolution reaction with long-term stability

BackgroundHigher purity of copper is produced by Electrowinning (EW) in the cathode. A major challenge in this technique is the anodic structure that causes in the energy consumption, corrosion resistance, and contamination of the copper produced in the cathode. MethodsTernary metallic oxide (IrO2-ZrO2-SiO2) composites with the different molar percentages of IrO2: SiO2 (10:60, 15:55, and 20:50%) were prepared on titanium substrate by the sol-gel technique, and then thermal decomposition to study the impact of IrO2 and SiO2 contents on the electrocatalyst performances of the dimensionally stable anodes (DSAs). The physicochemical properties of the DSAs were determined by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), Atomic force microscopy (AFM), and electrochemical measurements. Significant findingsFE-SEM and AFM images display the impact of SiO2 on the crystallization and crystal growth of IrO2, leading to the formation of finer oxide particles and the porous morphology of the ternary oxide coatings. The DSA composed of 50 % SiO2 and 20 % IrO2 (IZS (20–30–50)) with a more porous surface area represented high apparent electrocatalytic activity toward the oxygen evolution reaction with long-term stability as analyzed under cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and accelerated lifetime (ALT) plots.

Clarifying sequential electron-transfer steps in single-nanoparticle electrochemical process for identifying the intrinsic activity of electrocatalyst

Single-nanoparticle collision electrochemistry (SNCE) is an effective method for determining the intrinsic activity of electrocatalysts at the single-nanoparticle (NP) level. Despite fruitful advancements in the SNCE field, determining a quantitative relationship between the NP structure and its activity has remained difficult because of an unclear understanding of SNCE. In this study, we successfully uncovered the essential roles of the sequential electron-transfer steps in the SNCE system in regulating the apparent electrocatalytic activity of single NPs. By monitoring the oxygen reduction reaction of individual Pt NPs, significantly distinct apparent activities were observed at different electrodes owing to the rate-determining step-controlled electron transfer process. Furthermore, a new theoretical model is proposed for treating the electrochemical current, which involves NP-electrode electron transfer, heterogeneous electron transfer, and mass transfer in solution as sequential steps in the SNCE system. The combination of theoretical simulations and high-resolution electrochemical measurements allows for the corresponding parameters (contact resistance, heterogeneous kinetic constants, and adsorption possibility) of sequential electron-transfer steps to be quantified, resulting in the identification of a rate-determining step for improving the intrinsic activity of electrocatalysts. This work provides a clear picture for determining the intrinsic activity of single NPs in SNCE measurements and introduces a new conceptual route for the quantification of structure-activity relationships, which ultimately guide the rational design and optimization of electrocatalytic nanomaterials.

A Study on the Triangular-Wave Electrodeposition of Iridium Oxide on Ti

Iridium oxide is recognized as the best oxygen evolution anode material due to its excellent electrocatalytic activity and long-term stability in acidic environment. Electrodeposition, as a new method for preparing iridium oxide catalysts, has attracted extensive attention in recent years. We report a triangular-wave electrodeposition method for the preparation of iridium oxide electrodes and successfully synthesized highly active IrOx electrodes with ultralow iridium loading. The IrOx electrode prepared at 100 mV s−1 for 100 cycles exhibited a superior mass activity of 3.11 A mgIr −1, while the IrOx electrodeposited at 20 mV s−1 for 500 cycles has the best apparent electrocatalytic activity, Tafel slope as low as 54.75 mV dec−1. Physical characterization and electrochemical experiments show that the calcination treatment plays an important role in enhancing the OER performance of the electrodes. Remarkably, the calcined IrOx-TWE/Ti can continuously catalyze OER in 0.5 M H2SO4 at 50 mA cm−2 for 150 h with a slight performance decay, demonstrating a supper large stability number of This work provides some valuable insights into the application of electrodeposition-based iridium oxide to practical industrial systems.

Sensitive Determination of Trace 4-Nitrophenol in Ambient Environment Using a Glassy Carbon Electrode Modified with Formamide-Converted Nitrogen-Doped Carbon Materials.

Sensing trace amounts of 4-nitrophenol (4-NP) as a harmful substance to organisms even in small quantities is of great importance. The present study includes a sensitive and selective electrochemical sensor for detecting 4-NP in natural water samples using formamide-converted nitrogen-carbon materials (shortened to f-NC) as a new material for electrode modification. The structure and morphology of the f-NC were set apart by SEM, TEM, XRD, XPS, FTIR, Raman, and the electrochemical performance of the f-NC were set apart by CV, EIS and CC. We studied the electrochemical behaviour of 4-NP on the glassy carbon electrode modified with f-NC before and after pyrolysis treatment (denoted as f-NC1/GCE and f-NC2/GCE). In 0.2 M of H2SO4 solution, the f-NC2/GCE has an apparent electrocatalytic activity to reduce 4-NP. Under the optimal conditions, the reduction peak current of 4-NP varies linearly, with its concentration in the range of 0.2 to 100 mM, and the detection limit obtained as 0.02 mM (S/N = 3). In addition, the electrochemical sensor has high selectivity, and the stability is quite good. The preparation and application of the sensor to detect 4-NP in water samples produced satisfactory results, which provides a new method for the simple, sensitive and quantitative detection of 4-NP.

High Throughput Preparation of Ag-Zn Alloy Thin Films for the Electrocatalytic Reduction of CO2 to CO.

Ag-Zn alloys are identified as highly active and selective electrocatalysts for CO2 reduction reaction (CO2RR), while how the phase composition of the alloy affects the catalytic performances has not been systematically studied yet. In this study, we fabricated a series of Ag-Zn alloy catalysts by magnetron co-sputtering and further explored their activity and selectivity towards CO2 electroreduction in an aqueous KHCO3 electrolyte. The different Ag-Zn alloys involve one or more phases of Ag, AgZn, Ag5Zn8, AgZn3, and Zn. For all the catalysts, CO is the main product, likely due to the weak CO binding energy on the catalyst surface. The Ag5Zn8 and AgZn3 catalysts show a higher CO selectivity than that of pure Zn due to the synergistic effect of Ag and Zn, while the pure Ag catalyst exhibits the highest CO selectivity. Zn alloying improves the catalytic activity and reaction kinetics of CO2RR, and the AgZn3 catalyst shows the highest apparent electrocatalytic activity. This work found that the activity and selectivity of CO2RR are highly dependent on the element concentrations and phase compositions, which is inspiring to explore Ag-Zn alloy catalysts with promising CO2RR properties.

High catalytic performance of tungsten disulphide rodes in oxygen evolution reactions in alkaline solutions

Oxygen evolution reaction (OER) via electrocatalytic water splitting is crucial for efficient electrochemical energy storage and conversion. Herein, we describe the preparation of the rod-like structure of tungsten disulphide (WS2) as efficient catalysts for OER. Exfoliated tungsten disulphide was used as a source of the rods. The reshaping process required high-temperature treatment with the assistance of hydrogen and ethylene. We propose a structure with novel morphology and promising performance as an electrocatalyst. The rod-like structure was manifested by high-resolution transmission electron microscopy measurements including HAADF intensity line profile. Further structural insights were obtained in X-ray diffraction and Raman spectroscopy. The structures exhibited apparent electrocatalytic activity toward OER overpotential =351 mV at 10 mA/cm2 which is superior in respect to exfoliated tungsten disulphide (overpotential =564 mV at 10 mA/cm2).

Platinum Oxide Nanoparticles for Electrochemical Hydrogen Evolution: Influence of Platinum Valence State

Electrochemical hydrogen generation is a rising prospect for future renewable energy storage and conversion. Platinum remains a leading choice of catalyst, but because of its high cost and low natural abundance, it is critical to optimize its use. In the present study, platinum oxide nanoparticles of approximately 2 nm in diameter are deposited on carbon nitride (C3N4) nanosheets by thermal refluxing of C3N4 and PtCl2 or PtCl4 in water. These nanoparticles exhibit apparent electrocatalytic activity toward the hydrogen evolution reaction (HER) in acid. Interestingly, the HER activity increases with increasing Pt4+ concentration in the nanoparticles, and the optimized catalyst even outperforms commercial Pt/C, exhibiting an overpotential of only -7.7 mV to reach the current density of 10 mA cm-2 and a Tafel slope of -26.3 mV dec-1 . The results from this study suggest that the future design of platinum oxide catalysts should strive to maximize the Pt4+ sites and minimize the formation of the less active Pt2+ species.

Facile Synthesis of Fe/N/S‐Doped Carbon Tubes as High‐Performance Cathode and Anode for Microbial Fuel Cells

AbstractAs a renewable energy technology, microbial fuel cell (MFC) has been attracting increasing attention in recent decades. However, practical applications of MFCs has been hampered by the unsatisfactory electrode performance, in particular, at the cathode. Herein, Fe/N/S‐doped carbon hollow tubes were prepared by a facile two‐stage procedure involving hydrothermal treatment and pyrolysis at controlled temperatures. Electrochemical studies showed that the obtained samples exhibited an apparent electrocatalytic activity towards oxygen reduction reaction in both alkaline and acidic media, a performance comparable to that of commercial Pt/C, and the sample prepared at 800 °C stood out as the best among the series with a half‐wave potential of +0.81 V vs. RHE and an electron transfer number of 3.98 at +0.6 V vs. RHE. The Fe/N/S‐doped carbon tubes also exhibited a remarkable performance as an MFC anode by facilitating bacterial growth and electron transfer between the biofilm and electrode. In fact, an MFC based on the carbon tubes as both cathode and anode showed a markedly higher performance (maximum power density 479 W m−3) than the control MFC based on a graphene aerogel anode and Pt/C cathode (359 W m−3). These results suggest that Fe/N/S‐doped carbon composites can be used for the fabrication of high‐efficiency MFC electrodes.

Platinum-Free Electrocatalyst for Oxygen Reduction Reaction Derived from the Direct Pyrolysis of Watermelon Peels

Carbon-based nanomaterials derived from the pyrolysis of heteroatom-containing carbonaceous precursor was shown to exhibit significant electrocatalytic activity towards oxygen reduction reaction (ORR). Biomass from agricultural waste could be seen as possible low-cost precursor for the preparation of carbon-based ORR electrocatalysts. In this study, watermelon peels (WP) were directly pyrolyzed under N2 atmosphere to produce novel carbon-based ORR electrocatalysts. WP were oven-dried and pulverized using a mechanical grinder to produce WP powder. A weighed amount of the resulting powder was then transferred into a ceramic boat and inside a quartz tube furnace. The WP powder was pyrolyzed from room temperature to pyrolysis temperature T at a rate of 5 °C/min under N2 atmosphere. The temperature was held at T for an hour, followed by natural cooling back to room temperature. The pyrolysis temperature was optimized, with T = 800 °C, 900 °C, and 1000 °C. The resulting pyrolysis products were characterized using cyclic voltammetry (CV), rotating disc electrode voltammetry (RDE), and scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX). CV revealed that WP pyrolyzed at 1000 °C gave the most positive onset potential (Eonset = 0.40 V) and highest current density (j = 10.79 mA/cm2), compared to those pyrolyzed at 800 °C (Eonset = 0.30 V; j = 2.047 mA/cm2) and 900 °C (Eonset = 0.30 V; j = 3.494 mA/cm2). Levich analysis from RDE data showed that the electrocatalysts prepared at 1000 °C proceeded closest to the ideal four-electron route, compared to those prepared at 800 °C and 900 °C. SEM-EDX analysis showed the changes WP underwent in terms of surface morphology and elemental composition, which are then correlated with the apparent electrocatalytic activities of pyrolyzed WP. These findings present the feasibility of using WP as low-cost precursor for ORR electrocatalysts, which could be utilized in fuel cells.

Ethanol Electrooxidation Catalyzed by Tungsten Core@Palladium Shell Nanoparticles.

Bimetallic nanostructures represent effective electrocatalysts toward a number of important reactions. In the present study, carbon-supported palladium-tungsten alloy nanoparticles with a quasi-tungsten core@palladium shell structure (W@Pd/C) were synthesized by a galvanic replacement reaction of amorphous tungsten nanoparticles with Pd(II) at different temperatures (0, 25, and 50 °C), and exhibited apparent electrocatalytic activity toward ethanol oxidation reaction (EOR). When the sample was prepared at 0 °C, large amorphous tungsten nanoparticles were etched off and much smaller W@Pd nanoparticles were formed and dispersed rather evenly on the carbon surface whereas at higher reaction temperatures (25 and 50 °C), the W@Pd nanoparticles became agglomerated. The structures of the obtained samples were characterized by a range of experimental tools, including (scanning) transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical methods. Among the series, the W@Pd/C sample prepared at 0 °C was observed to exhibit the best EOR performance, with a mass activity (9535.5 mA mgPd-1) over three times better than that of commercial Pd/C and markedly enhanced stability.

A series of germanotungstate-based 3d-4f heterometallic compounds with visible-light induced photocatalytic, electrochemical and magnetic properties

A series of 3d-4f heterometallic germanotungstate dimers {[Cu(dap)(H2O)3][LnCu3(dap)3(OH)3(H2O)2(GeW11O39)]}⋅nH2O (Ln = SmⅢ, n = 11 (1), EuⅢ, n = 12 (2), GdⅢ, n = 10 (3) and TbⅢ, n = 13 (4); dap = 1, 2-diaminopropane) have been prepared under hydrothermal conditions and structurally characterized by IR, UV–Vis, XRD, and X-ray single-crystal diffraction. Compounds 1–4 are essentially isomorphic and display organic-inorganic hybrid dimeric structures consisting of [LnCu3(dap)3(OH)3(H2O)(GeW11O39)]24− with two supporting [Cu(dap)(H2O)3]2+ cations on both sides. The four compounds all exhibit the excellent photocatalytic activities to degradation of methylene blue (MB) and rhodamine-B (RhB) under visible light irradiation in the presence of H2O2. Additionally, 1–4 displays an apparent electrocatalytic activity for the reduction of hydrogen peroxide. The variable-temperature magnetic studies show that the magnetic behaviours of 1, 2 and 4 are dominated by antiferromagnetic coupling interactions, while that of 3 is ferromagnetic interactions coexist along with antiferromagnetic interactions.

Dual doping of mesoporous carbon pillars with oxygen and sulfur as counter electrodes for iodide/triiodide redox mediated dye-sensitized solar cells

Pillar-like mesoporous carbon doped with oxygen and sulfur heteroatoms was obtained through thermal pyrolysis of a zinc-based metal-organic framework, Zn-BTC (BTC = 1,3,5-benzenetricarboxylic acid), followed by acid treatment and sulfurization. The pillar morphology remained after acid etching and sulfur doping, while the content of disordered carbon and the structural defects were significantly increased, resulting in an increase in the electroactive sites for catalyzing the iodide/triiodide ions. In addition, the incorporation of sulfur heteroatoms into carbon frameworks could cause the reduction of oxygen-doped carbon pillars, improving the apparent electrocatalytic activity. The cyclic voltammetry and electrochemical impedance spectroscopy showed that the oxygen and sulfur dual-doped (OS-doped) carbon electrode has better electrocatalytic performance than the single oxygen doped (O-doped) carbon electrode, probably owing to the sulfur doping in carbon matrix that offered abundant electroactive site for boosting the iodide/triiodide redox shuttle. Dye-sensitized solar cell employing OS-doped carbon exhibited power conversion efficiency of 10.2%, greater than that using Pt (9.4%), O-doped carbon (8.0%), and ZnO-doped carbon (7.7%).

Oxygen reduction reaction and hydrogen evolution reaction catalyzed by carbon-supported molybdenum-coated palladium nanocubes

Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are two important processes for electrochemical energy storage and conversion. Herein, we describe the preparation of carbon-supported Pd nanocubes@Mo core@shell nanostructures as efficient dual catalysts for both ORR and HER. The core@shell structure was manifested by high-resolution transmission electron microscopy measurements, including high angle-angular dark field-scanning transmission electron microscopy and elemental mapping analysis. Further structural insights were obtained in X-ray diffraction and X-ray photoelectron spectroscopy measurements. The nanostructures exhibited apparent electrocatalytic activity toward both ORR and HER, and the performances were markedly higher than those without the deposition of a Mo overlayer. In ORR, the activity was even better than that of commercial Pt/C within the context of onset potential, specific and mass activities; whereas in HER, the performance of Pd nanocubes@Mo core@shell nanostructures remained subpar as compared to that of Pt/C in terms of the overpotential to reach the current density of 10 mA cm−2, the Tafel slope was comparable and the stability was excellent. The excellent electrocatalytic performance can be attributed to the Pd-Mo synergistic effects imparted from the core-shell structure.

Hydrogen evolution reaction catalyzed by ruthenium ion-complexed graphitic carbon nitride nanosheets

With the incorporation of ruthenium metal ions into the molecular skeleton by Ru–N coordination bonds, carbon nitride nanosheets exhibit apparent electrocatalytic activity towards hydrogen evolution reaction.

Single Atom Modified Covalent Triazine Frameworks As Electrocatalysts

Covalent organic frameworks (COFs) are cross-linked porous polymers, which have great potential in catalysis area because of their unique porous structure (i.e. high surface area), mechanical robustness and high design flexibility. Especially, covalent triazine frameworks (CTFs), which have 1,3,5-triazine structure as units, possess the high density of nitrogen (N) atoms in their organic pore for metal coordinations [1,2]. Recently, Palkovits et al. reported that platinum-modified CTF (Pt-CTF) functioned as a solid catalyst for the selective low-temperature oxidation of methane to methanol [3]. In general, the oxidation of methanol can easily proceed compared to methane oxidation because the C-H bond energy of methanol is much smaller than that of methane. Thus, the catalytic activity for methane partial oxidation to methanol let us assume that Pt-CTF has no activity to oxidize methanol (i.e. methanol tolerance).The methanol tolerance is the essential property for the cathode catalyst of direct methanol fuel cells (DMFC) as the methanol-crossover effect is one of the issues to be addressed. However, the application of the frameworks as electrocatalysts has not been achieved to date because of their poor electrical conductivity. In the present work, we have successfully applied CTF-based materials to electrocatalysts by hybridizing non-conductive CTFs with conductive carbon particles (CPs). The hybridized material was obtained by the polymerization of CTFs on CPs in molten ZnCl2. Then, Pt atoms were grafted in the pore of CTFs by the impregnated with platinum chloride.Then, Pt atoms were grafted in the pore of CTFs by the impregnated with platinum chloride (Pt-CTF/CP). The resulting catalyst showed apparent electrocatalytic activity for oxygen reduction reaction (ORR). In case of a commercial 20 wt% Pt/C, after the addition of 1 M CH3OH, the onset potential of the cathodic current shifted approximately 200 mV in the negative direction in the presence of oxygen (Figure, inset). In contrast, surprisingly, the overlap of the CH3OH oxidation current with that of the ORR was almost negligible for Pt-CTF/CP even in the presence of 1 M CH3OH as shown in the Figure [4]. These results clearly showed that Pt-CTF/CP exhibited a high methanol tolerance during the ORR, as we expected. This is the first demonstration of the potential for CTF-based materials to serve as electrocatalysts. The extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) results demonstrated that the Cu atoms in Cu-CTF/CP are singly isolated. It has been reported that at least two adjacent Pt sites are required for methanol oxidation. Actually, to the best of our knowledge, there are no works that reported the possibility of the methanol oxidation on single Pt-atom site. Thus, the structural feature of single Pt atoms, which were stabilized by N atoms in the CTF pores, is likely the origin of the methanol-tolerance. [1] K. Iwase, K. Kamiya et al., Angew. Chem. Int. Ed. 38, 11068, (2015)[2] T. Yoshioka, K. Kamiya et al., J. Phys. Chem. C in press. 10.1021/acs.jpcc.5b10962[3] Palkovits et al. Angew. Chem. Int. Ed. 48, 6909, (2009)[4] K. Kamiya et al. Nat. Commun. 5, 5040, (2014) Figure 1

Impacts of oxygen vacancies on the electrocatalytic activity of AuTiO2 nanocomposites towards oxygen reduction

Nanocomposites based on metal nanoparticles supported on oxide surfaces have been used extensively as effective catalysts for fuel cell electrochemistry. In this study, functional nanocomposites based on gold nanoparticles deposited onto TiO2 colloids were prepared by a simple wet chemistry method, and subject to hydrothermal treatment at a controlled temperature in the presence of ascorbic acid. Transmission electron microscopic measurements showed that the gold nanoparticles (10–30 nm in diameter) were embedded within the TiO2 matrix consisting of colloids of 5–10 nm in diameter and anatase crystalline structures, as evidenced in x-ray diffraction studies. Interestingly, electron paramagnetic resonance measurements showed the formation of oxygen vacancies after hydrothermal treatment and the concentrations of oxygen vacancies increased with the amount of ascorbic acid added. Consistent results were obtained in x-ray photoelectron spectroscopic measurements, which suggested partial charge transfer from gold to oxygen-deficient TiO2. The Au:Ti atomic ratio in the nanocomposites was estimated to be ca. 11% and consistent among the series of samples. Electrochemically, the nanocomposites exhibited apparent electrocatalytic activity towards oxygen reduction reactions in alkaline media, which showed a peak-shaped variation with the concentration of the oxygen vacancies. This was accounted for by the deliberate manipulation of the binding energy of oxygen species onto the nanocomposite surfaces. In addition, the AuTiO2 nanocomposites exhibited markedly enhanced tolerance against methanol crossover, as compared to commercial Pt/C catalysts.

Synthesis, structure and electrochemical properties of an inorganic–organic hybrid CuII[sbnd]CeIII heterometallic germanotungstate

A new 1:2-type inorganic–organic hybrid CuIICeIII heterometallic germanotungstate (GT) derivative KNa2H9[enH2]2 [Cu(en)2(H2O)]2[Cu(en)2]2{Cu(en)2[Ce(α-GeW11O39)2]2}·14H2O (1) (en=ethylenediamine) was obtained by simultaneously introducing Cu2+ and Ce4+ cations to the trivacant Keggin-type [A-α-GeW9O34]10− system in the help of extra Na2WO4·2H2O and en ligand under hydrothermal conditions and was further characterized by elemental analyses, IR spectrum, thermogravimetric (TG) analysis and single-crystal X-ray diffraction. 1 exhibits a 1-D CuIICeIII heterometallic chain architecture by tetrameric {Cu(en)2[Ce(α-GeW11O39)2]2}24− units via K+ cations. Moreover, its solid-state electrochemical and electrocatalytic properties have been measured in 0.5molL−1 Na2SO4+H2SO4 aqueous solution by entrapping them in a carbon paste electrode, indicating that 1 displays apparent electrocatalytic activities for nitrite, bromate and hydrogen peroxide reduction.

Ultra-small Fe2N nanocrystals embedded into mesoporous nitrogen-doped graphitic carbon spheres as a highly active, stable, and methanol-tolerant electrocatalyst for the oxygen reduction reaction

A low-cost, highly active, stable, and methanol tolerant electrocatalyst towards the oxygen reduction reaction (ORR) is extremely desirable for promoting the commercialization of fuel cells. Herein, we reported a facile two-step pyrolysis and acid leaching process to synthesize a high performance ORR electrocatalyst, where ultra-small Fe2N nanocrystals were incorporated into mesoporous nitrogen-doped graphitic carbon spheres (MNGCS). The Fe2N/MNGCS electrocatalysts with difference Fe2N contents and BET surface areas were obtained via altering the acid leaching time, and all exhibited the apparent electrocatalytic activity. The optimized ORR activity was achieved over (Fe2N/MNGCS)4 with the positive half-wave potentials (0.881V vs RHE), high selectivity (4 e− process), excellent long-term stability (95.2% of the initial current remaining after 60,000s of continuous operation) and good tolerance against methanol-crossover effect (94.9% of the current retained prior to 4.0M methanol injection) in alkaline media, which even was more superior to that of commercial Pt/C catalyst. The remarkable ORR activity was originated from the cooperative effect of ultra-small Fe2N nanocrystals and MNGCS, where the balance of catalytic active site density, mesoporous structure, BET specific surface area, and electron conductivity played a key role in determining the ORR performance.

Graphene-Supported Mesoporous Carbons Prepared with Thermally Removable Templates as Efficient Catalysts for Oxygen Electroreduction.

Graphene-supported mesoporous carbons with rich nitrogen self-doped active sites (N-MC/rGO) are prepared by direct pyrolysis of a graphene-oxide-supported polymer composite embedded with massive, evenly distributed amorphous FeOOH that serve as efficient thermally removable templates. The resulting N-MC/rGO catalysts exhibit high surface areas and apparent electrocatalytic activity for oxygen reduction reaction in alkaline media. Among the series, the sample prepared at 800 °C displays the best performance with a more positive onset potential, higher limiting currents, much higher stability, and stronger poison resistance than commercial Pt/C. This is ascribed to the synergetic functions of the highly conductive graphene support and the mesoporous N-doped carbons that effectively impede the restacking of the graphene sheets and enhance the exposure of the rich nitrogen self-doped active sites.

Controlling the Morphology and Efficiency of Nanostructured Molybdenum Nitride Electrocatalysts for the Hydrogen Evolution Reaction

AbstractAmong catalysts based on non‐noble metals, Mo‐based materials are important for hydrogen evolution because of their low cost, good conductivity, and catalytic efficiency. This study demonstrates a facile two‐step synthesis of Mo2N nanostructures assembled from 5–8 nm particles with graphitic carbon nitride as the nitrogen source. These Mo2N nanostructures of various morphologies (hexagons, triangles, and nanowires) show a very high activity and stability in acidic media during water electrolysis. Their nanostructures were characterized by using powder XRD, electron microscopy, N2 gas adsorption analysis, and X‐ray photoelectron spectroscopy. Hydrogen evolution reaction parameters, which include the Tafel slope, charge transfer resistance, and stability, were analyzed by using linear sweep voltammetry and electrochemical impedance spectroscopy. Thin hexagonal sheets of Mo2N show the highest apparent electrocatalytic activity (current density of 197 mA cm−2geometric at −400 mV vs. the reversible hydrogen electrode) and excellent stability in an acidic medium with a small onset potential of 90 mV and a Tafel slope of 145 mV decade−1. The lowest Tafel slope was observed for Mo2N nanowires.