Onset Potential Values Research Articles

Orbital symmetry matching: Achieving superior nitrogen reduction reaction over single-atom catalysts anchored on Mxene substrates

The nitrogen reduction reaction (NRR) under ambient conditions is still challenging due to the inertness of N2. Herein, we report a series of superior NRR catalysts identified by examining Ti2NO2 MXenes embedded with 28 different single-atom catalysts using first-principles calculations. The stability of this system was first verified using formation energies, and it is discovered that N2 can be effectively adsorbed due to the synergistic effect between single atom catalysis and the Ti atoms. Examination of the electronic structure demonstrated that this design satisfies orbital symmetry matching where “acceptor-donor” interaction scenario can be realized. A new “enzymatic-distal” reaction mechanism that is a mixture of the enzymatic and distal pathways was also discovered. Among all of the candidates, Ni anchored on MXene system achieves an onset potential as low as −0.13 V, which to the best of our knowledge is the lowest onset potential value reported to date. This work elucidates the significance of orbital symmetry matching and provides theoretical guidance for future studies.

Strategy for enhancing the hydrogen evolution reaction properties of $$\hbox {MoS}_{\mathrm {2}}$$ by utilizing the ordered mesoporous carbon as support and modification with nickel

Surface modification of electrocatalyst suitable for yielding reduced overpotential with improved exchange current density at the interface is highly desired for hydrogen evolution reaction (HER). Herein, the present report demonstrates the HER performance of ordered mesoporous carbon (OMC)-supported nickel-modified $$\hbox {MoS}_{\mathrm {2}}$$ electrocatalysts [NiMoS(x)–OMC] synthesized by hydrothermal route. Inherent activity of pristine $$\hbox {MoS}_{\mathrm {2}}$$ was improved by two vital surface strategies utilizing OMC as the support matrix for the dispersed growth of active catalyst and surpassing the active sites formation via augmentation of various concentrations of nickel. Crystalline phase, heterostructure vibrations, morphological orientation and electrocatalytic property of the prepared catalysts are comprehensively studied using different spectroscopic methods. Linear sweep voltammetric analysis suggests that the HER from the pristine $$\hbox {MoS}_{\mathrm {2}}$$ could be amplified by introducing OMC as support matrix. Synergistic enrichment of Ni (3 and 5 wt%) on $$\hbox {MoS}_{\mathrm {2}}$$ –OMC matrix enables both the lowest onset potential (180 and 185 mV) and Tafel slope values (103 and 100 mV per decade), with retained stability promising for further optimization and scalability.

Sorbitol electro-oxidation reaction on sub

Sorbitol is a highly available and functionalized polyalcohol, with vast industrial usages and with great potential for fuel cells application. However, few studies have been done regarding its electrochemical oxidation. In this work, monometallic Au, Pt and PtAu with different compositions from Pt‒rich (such as Pt85Au15) to Au‒rich (Pt10Au90) nanomaterials were synthesized. Several parameters like sorbitol and KOH concentration, scan rate, charge-transfer resistance, and temperature were tested. According with the physicochemical characterization, average particle sizes from 5.6 to 6.5 nm were found for all electrocatalysts, while Pt atomic percentages of 85, 60, 40, and 10% were obtained. X‒ray photoelectron spectroscopy revealed shifts in Pt 4f and Au 4f core‒levels related to electron density changes by the interaction between these elements and as a result, the electrocatalytic properties for the sorbitol electro‒oxidation reaction (SOR) were modified. The PtAu nanomaterials presented an increase of the current density with the raise of the KOH and sorbitol concentrations, being Pt40Au60/C the most active electrocatalyst displaying 40 mA mg−1 at 0.1 M sorbitol in 2 M KOH with an onset potential of −0.50 V vs. NHE. This onset potential value was more negative to that typically reported for other polyols like glycerol and ethylene glycol. The reaction pathway of Pt/C, Au/C and Pt40Au60/C was followed by chromatographic and spectroscopic techniques, finding that the complex surfaces of these electrocatalysts were capable to carry the SOR via several electrons (from 2 to 24 e−). In this manner, the high electrocatalytic activity of Pt40Au60/C was attributed to the electron density changes that promote a higher electron transfer forming shorter‒chain byproducts.

Promotional effect of Ni–Co/ordered mesoporous carbon as non-noble hybrid electrocatalyst for methanol electro-oxidation

The development of a ternary hybrid catalytic system, inclusive of Ni species/Co species/ordered mesoporous carbon (catalyst/co-catalyst/support) and its promotional & synergistic impact towards methanol electro-oxidation has been reported. High surface area, soft template synthesized, ordered Mesoporous Carbon, was used as a scaffold. 15 wt% of Ni or/& Co was/were deposited onto the pre-synthesized carbon scaffold in varying ratios viz. Ni, 1Ni3Co (1:3), 1Ni1Co (1:1), 3Ni1Co (3:1) and Co. Via physicochemical characterization techniques, the phase purity, specific surface area, the extent of agglomeration, and its chemical functionality were quantified. Cyclic Voltammetry, Electrochemical Impedance, and Chronoamperometry techniques collectively exhibited the synergistic impact and the benefit of mixing the two metal systems (Ni & Co) together. Two identical sets of catalysts were synthesized; one from metal nitrate & the other from metal chloride precursors. Highest current density (151.51 mA cm−2) & lowest onset potential (0.27 V) values were recorded when Ni:Co was taken in 1:3 elemental wt% ratio & synthesized from the nitrate based inorganic metal precursors; this observation can be attributed to the higher content of amorphous borate shell layer formed in the nitrate as compared to the chloride precursor based catalysts.

High power density and improved H2 evolution reaction on MoO3/Activated carbon composite

The formation of hexagonal MoO3 (h- MoO3) microrods was favoured at lower pH in the hydrothermal synthesis method. Symmetric and Hybrid supercapacitors were fabricated using h-MoO3/plastic bottle derived activated carbon (PAC) composite in 1 M Na2SO4 aqueous electrolyte. The operating voltage for the aqueous electrolyte was maximized to 1.6 V with this combination. The wide operating voltage led to a maximum specific capacitance of 211 Fg-1, power density of 287 W kg−1 and 79% efficiency even at 5000 charge-discharge cycles for the hybrid supercapacitor combination. The combined effect of PAC micropores along with the 1-D rod-shaped h-MoO3, helped in faster charge-transfer, hence increasing the efficiency of supercapacitors. Further, the composites of defective PAC (PDAC) together with the h-MoO3 when tested for hydrogen evolution reactions (HER), provided lesser onset potential and Tafel slope values of −0.23 mV and −93 mVdec−1. There was a change in the structural environment of carbon due to the heteroatom doping and dedoping producing defects in PAC, termed as PDAC. These defects together with the hexagonal microrods of MoO3 provided fast electron transfer towards hydrogen adsorption/desorption hence effectively producing H2.

Porous 3D flower-like bismuth silicate@nitrogen-doped graphene nanomaterial as high-efficient catalyst for fuel cell cathode

Three-dimensional (3D) flower-like Bi2SiO5 nanomaterials (FLB) and 3D flower-like Bi2SiO5@nitrogen doped graphene nanomaterials (FLBNG) have been originally synthesized. Notably, as-synthesized FLB and FLBNG nanomaterials have not yet been discussed in previous reports. The FLBNG nanomaterials have been for the first time studied as the cathodic catalysts for Fuel cell. Research results have shown that the FLBNG-2 possesses perfectly 3D flower-like Bi2SiO5 with numerous uniformly coiled nanowires and exhibits good methanol immunity, high activity and high durability during oxygen reduction reaction (ORR) process under acidic and basic electrolytes. The value of onset potential (E0) for FLBNG-2 in alkaline electrolyte can reach to 1.091 V, Tafel slope of FLBNG-2 is 45.637 mV dec−1 and its limiting current density (JL) is 6.49 mA cm−2. Similarly, These ORR performances in acidic electrolyte are also better than those of 20 wt% commercial Pt/C and most of the associated reports. Thus, the FLBNG-2 could be a potential ORR catalyst, applied in the cathode of fuel cells to enhance the kinetic rate, decrease costs and enhance durability. And this synthesis method may be provide a good design to synthesize other 3D flower-like nanomaterials with desirable properties.

Bimetallic transition metal chalcogenide nanowire array: An effective catalyst for overall water splitting

The development of highly active, durable, and inexpensive bifunctional catalysts towards both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is one of the most challenging tasks in the term of renewable energy. Keeping in mind the current scenario, herein, we have synthesized bimetallic transition metal chalcogenides (CoTe2@CdTe and CoSe2@CdSe) by a very easy, single step hydrothermal process. During the synthesis, two different morphologies (i.e. spherical and wire) were obtained depending on the selection of chalcogen. It was found that Te based nanocomposite i.e. CoTe2@CdTe showed a symmetrical nanowire array morphology with a high electrocatalytic surface area and good electrocatalytic activity towards both HER and OER. The structural, morphological and electrochemical features of synthesized nanocomposites were characterized by various useful techniques (like field emission scanning electron microscopy, high resolution transmission electron microscopy, powder X-ray diffraction analysis etc.) to confirm their successful synthesis. The CoTe2@CdTe nanowire array has shown a small onset potential value, high current density, low Tafel slope value along with high stability towards overall water splitting.

Self‐Assembled Monolayer Stabilized Gold‐Vanadate Nanoflute for Water Splitting Reactions

AbstractVanadium oxide (VOx) decorated with gold‐nanoparticles via self‐assembled monolayer approach is herein reported to be an efficient electrocatalyst for both oxygen and hydrogen evolution reactions (OER and HER) in alkali medium. The voids created in the nanoflute of gold‐vanadate were believed to be responsible for high mass transfer allowing the material to be highly applicable as a catalyst for water splitting and nitro‐arene reduction. The nanoflute exhibited high current density with low onset potential value in both OER and HER. The overpotential value at 10 mAcm−2 was observed to be 310 mV with onset potential of 1.43 V in case of OER while the overpotential value for HER was measured to be 282 mV. The nanocatalyst was found to be stable upto 10 h with minimal increment in the overpotential value. The Tafel plot value of 127 mVdec−1 in OER and 131 mVdec−1 in HER also signified for the high efficacy of the catalyst towards splitting of water molecules under high basic condition. The same material was also used as catalyst for reduction of various nitro‐arenes in isopropanol with 0.25 M KOH. The liberation of hydrogen via the oxidation of isopropanol was supposed to be responsible for reduction of nitro‐arenes. The ability of the catalyst to oxidize isopropanol was substantiated from electrochemical studies.

MoS2-graphene-CuNi2S4 nanocomposite an efficient electrocatalyst for the hydrogen evolution reaction

We present a facile methodology for the synthesis of a novel 2D-MoS2, graphene and CuNi2S4 (MoS2-g-CuNi2S4) nanocomposite that displays highly efficient electrocatalytic activity towards the production of hydrogen. The intrinsic hydrogen evolution reaction (HER) activity of MoS2 nanosheets was significantly enhanced by increasing the affinity of the active edge sites towards H+ adsorption using transition metal (Cu and Ni2) dopants, whilst also increasing the edge sites exposure by anchoring them to a graphene framework. Detailed XPS analysis reveals a higher percentage of surface exposed S at 17.04%, of which 48.83% is metal bonded S (sulfide). The resultant MoS2-g-CuNi2S4 nanocomposites are immobilized upon screen-printed electrodes (SPEs) and exhibit a HER onset potential and Tafel slope value of – 0.05 V (vs. RHE) and 29.3 mV dec−1, respectively. These values are close to that of the polycrystalline Pt electrode (near zero potential (vs. RHE) and 21.0 mV dec−1, respectively) and enhanced over a bare/unmodified SPE (– 0.43 V (vs. RHE) and 149.1 mV dec−1, respectively). Given the efficient, HER activity displayed by the novel MoS2-g-CuNi2S4/SPE electrochemical platform and the comparatively low associated cost of production for this nanocomposite, it has potential to be a cost-effective alternative to Pt within electrolyser technologies.

Binary and Ternary Nanocubes As Electrocatalysts for Ammonia Electrooxidation Reaction

Ammonia electrooxidation reaction (AOR) plays a pivotal role in H2 production, direct ammonia fuel cells, electrosynthesis, electrochemical sensors as well as understanding of nitrogen cycle.1-2 AOR kinetics is slow requiring electrocatalysts among which Pt and Ir are the two best choices.2 AOR is also very sensitive to structure of electrocatalyst as (100) facets exhibit maximum activity.3-4 Among alloys, PtIr has shown the best performance but there are inconsistent reports on the amount of Ir required for enhancing the activity.5 Designing more durable electrocatalysts for AOR has also been a bottleneck. In this context, Ni could be a possible solution according to a report based on theoretical calculations.6 In this study, PtIr (several ratios), PtNi and PtIrNi cubic electrocatalysts with (100) facets were prepared by wet chemistry methods with CO as selective capping agent. Structure, morphology and composition of the obtained electrocatalysts were examined by TEM, EDX, XRD and ICP-AES. Quantitative estimation of (100) surface sites were carried out by GeO2 irreversible adsorption and analysis of H desorption peaks in KOH solution. Currents shown in Figure 1 were normalized by electrochemical surface areas obtained via the Cu UPD method. LSV and chronoamperometry methods were used to elucidate the activity and stability of electrocatalysts, respectively. It was found that only a trace amount of Ir could increase the activity of Pt cubes by more than twice. As illustrated in Figure 1, PtIr (85:1) cubes exhibited specific activity of 1.25 mA cm-2 compared to Pt cubes with 0.58 mA cm-2. Increasing the amount of Ir further decreased the activity. PtNi cubes performed better than Pt cubes with respect to stability although its specific activity of 0.51 mA cm-2 was slightly less than Pt cubes. Addition of trace amount of both Ir and Ni to Pt cubes, i.e. ternary PtIrNi cubes demonstrated the best performance in terms of stability. These PtIrNi cubes had specific activity of 0.72 mA cm-2 which was 41% more than Pt cubes. Additionally, PtIr cubes showed the least value of onset potential which was 0.429 V vs RHE as can be seen in Figure 1. This work adds new insights showing that a minute amount of Ir could improve the AOR of Pt significantly. Furthermore, Ni plays a crucial role in improving stability for AOR. Figure 1. LSVs of electrocatalysts in 0.1M KOH + 0.1M NH3 aqueous solution at 50 mV s-1 References Zhong, C., Hu ,W. B., and Cheng Y. F., Journal of Materials Chemistry A 2013, 10, 3216-3238.Siddharth, Kumar, Yattung Chan, Lu Wang, and Minhua Shao, Current Opinion in Electrochemistry 2018, Vol 9, 151-157.Liu, J., Fan, X., Liu, X., Song, Z., Deng, Y., Han, X., Hu, W. and Zhong, C., ACS applied materials & interfaces 2017, 9(22), pp.18856-18864.Zhang, C., Hwang, S.Y. and Peng, Z., Journal of Materials Chemistry A 2013, 1(45), pp.14402-14408.Li, Z.F., Wang, Y. and Botte, G.G., Electrochimica Acta 2017, 228, pp.351-360.Yang, Y., Yu, H., Cai, Y., Ferrando, R. and Cheng, D., Journal of Physics: Condensed Matter 2018, Vol 30(28). Figure 1

Phase‐Controlled Cobalt Phosphide Nanoparticles Coupled with N, P, S Co‐Doped Hollow Carbon Polyhedrons as Efficient Catalysts for Both Alkaline and Acidic Hydrogen Evolution

Tailoring cobalt phosphide electrocatalysts with a tunable phase and morphology is of great importance for the advancement of hydrogen evolution reaction (HER). The synthesis of phase‐ and morphology‐modulated hollow cobalt phosphide nanoparticles coupled with N, P, S co‐doped carbon (Co‐P@NPS‐C) polyhedrons through a facile three‐step method is reported. Benefiting from the cooperation of structural features, heteroatoms doping, and catalytic components (CoxP, a mixture of CoP and Co2P), the hollow CoxP@NPS‐C polyhedrons exhibit superior HER performance and long‐term stability in 1.0 m KOH solution, with a low onset potential value (18 mV), an overpotential of 80 mV at 10 mA cm−2, and a small Tafel slope of 57.6 mV dec−1. In addition, the CoxP@NPS‐C electrodes exhibit good electrochemical properties and stability in 0.5 m H2SO4 solution. These results suggest a novel and promising coating approach with poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol (PZS) to fabricate other heterogeneous catalysts for various applications.

Improved electrocatalytic kinetics of nickel hydroxide nanoparticles on Vulcan XC-72R carbon black towards alkaline urea oxidation reaction

Nickel hydroxide nanoparticles were fabricated on Vulcan XC-72R carbon black using various reducing agents through assisted microwave polyol process. The formed electrocatalysts using sodium borohydride [Ni(OH)2/C–NB], ethylene glycol [Ni(OH)2/C–EG] and a mixture of them [Ni(OH)2/C–EGNB] displayed an electrocatalytic activity towards urea oxidation in NaOH solution. The oxidation peak potential and current density values were greatly influenced by the employed reducing agent. Lower onset and peak potential values were measured at Ni(OH)2/C–EGNB, while Ni(OH)2/C–EG exhibited the highest oxidation current density during urea oxidation reaction. Electroactive surface area measurements revealed that the number of available active sites for the oxidation reaction was arranged in an ascending order as Ni(OH)2/C–NB < Ni(OH)2/C–EGNB < Ni(OH)2/C–EG. The diffusion coefficient of urea molecules at Ni(OH)2/C–EG and Ni(OH)2/C–EGNB was 14.69 and 5.90 times higher than that at Ni(OH)2/C–NB. Stable performance was measured at all studied electrocatalysts over prolonged operation suggesting their valuable application as efficient anode materials in direct urea oxidation fuel cells.

In situ growth of M-MO (M = Ni, Co) in 3D graphene as a competent bifunctional electrocatalyst for OER and HER

In this study, an efficient and cheap electrocatalysts are prepared by a simple synthetic method for oxygen evolution reaction (OER) hydrogen evolution reaction (HER). Nickel/nickel oxide@3dimensional hierarchical porous graphene (Ni-NiO@3DHPG) and cobalt/cobalt oxide@3dimensional hierarchical porous graphene (Co-CoO@3DHPG) electrocatalysts were obtained from cation exchange resin, nickel acetate and cobalt nitrate as a source of carbon, Ni and Co respectively. In Ni-NiO@3DHPG and Co-CoO@3DHPG, metal and metal oxide nanoparticles embedded in the graphene layers, were confirmed by different techniques. The 3-D graphene in Ni-NiO@3DHPG and Co-CoO@3DHPG were thinned wall and highly porous structure and large specific surface area. The Ni-NiO@3DHPG composite displays onset potential, overpotential (10 mA cm−2) and Tafel value of are 1.53 V, 1.64 V and 55 mV dec−1 for OER and −0.18 V, −0.31 V and 78 mV dec−1 for HER respectively. Similarly, Co-CoO@3DHPG catalyst show onset potential, overpotential (10 mA cm−2) and Tafel are 1.59 V, 1.68 V and 65 mV dec−1 for OER and −0.26 V, −0.40 V and 85 mV dec−1 for HER respectively. Electrocatalysts show good stability after 4 h continuously. This simple synthetic method will open a new way for cheap and efficient electrocatalysts of other types of non-precious metals for OER and HER.

Evaluation of core-shell structured cobalt@platinum nanoparticles-decorated graphene for nitrite sensing

A new graphene composite was fabricated with cobalt (core) and platinum (shell) nanoparticles [Co@Pt/Gr] in two-steps preparation method. This prepared electrode combined the enhanced electrocatalytic activity of platinum, increased electrical conductivity of cobalt and high surface area of graphene. Compared with Pt/Gr, Co@Pt/Gr exhibited lowered onset potential value for nitrite oxidation in 0.1 M phosphate buffer solution with increased current density. Some related kinetic parameters for nitrite oxidation at Co@Pt/Gr electrode were calculated including Tafel slope, the exchange current density, the diffusion coefficient and the heterogeneous electron transfer rate constant values. Amperometry measurements demonstrated wide linear nitrite concentration ranges as 1 μM–2 mM and 2–15 mM with remarkably increased sensitivity values of 45.96 and 97.71 μA mM−1 cm−2, respectively. Co@Pt/Gr electrode showed a selective response for nitrite determination in presence of common interferents. The reproducibility and stability experiments also revealed good results suggesting Co@Pt/Gr electrode for effective and valuable detection of nitrite in medicine and environmental chemistry.

Layered Nickel-Cobalt Oxide Coatings on Stainless Steel as an Electrocatalyst for Oxygen Evolution Reaction

In this work, we have obtained spinel-type nickel-cobalt oxide nanostructures on low-cost and easy-handling AISI304-type stainless steel substrate via simple potentiostatic electrodeposition. Nickel and cobalt hydroxide layers were formed by varying the deposition potential at the same time intervals (− 1.15 V for Ni(OH)2 and − 0.85 V for Co(OH)2). An electrolyte bath containing 0.05 M Ni(NO3)2, 0.05 M Co(NO3)2, and 0.1 M KNO3 was used for the electrodeposition. Structural analysis confirmed the formation of a spinel NiCo2O4 after thermal treatment. The influence of annealing temperature in the range of 473–1073 K on the films activity in OER has been investigated using 0.1 M NaOH. Nickel-cobalt oxide coatings demonstrated OER activity close to the benchmark IrO2 with the onset potential value of + 1.6 (vs. RHE), overpotential of 530 mV at 10 mA cm−2, and Tafel slope of 49 mV dec−1. Meanwhile, the electrocatalytic activity of separate Co3O4 and NiO is far smaller.

Efficient Photoelectrochemical Water Oxidation on Hematite with Fluorine‐Doped FeOOH and FeNiOOH as Dual Cocatalysts

An effective cocatalyst is usually required to improve the performance of photoelectrochemical (PEC) water splitting catalysts. A fluorine-doped FeOOH (F:FeOOH) cocatalyst on a hematite photoanode was used to lower the onset potential by 140 mV and significantly improve the PEC performance. Moreover, a more effective dual cocatalytic system was prepared by subsequent loading of a FeNiOOH cocatalyst, which resulted in a further decrease of the onset potential by 270 mV. The final onset potential of the Fe2 O3 /F:FeOOH/FeNiOOH photoanode was lowered to 0.45 V versus the reversible hydrogen electrode (RHE), which is one of the lowest onset potential values ever reported for hematite photoanodes. The photocurrent also dramatically increased by a factor of approximately 3 to 0.9 mA cm-2 at 1.0 V versus RHE. Based on the structural, chemical, and electrochemical impedance spectroscopy characterization, the enhanced performance was attributed to the F:FeOOH overlayer, which reduced the surface recombination and accelerated the oxygen evolution reaction activity, and the FeNiOOH cocatalyst, which further enhanced the reaction kinetics. The facile preparation of the F:FeOOH cocatalyst and the design of the dual cocatalytic system will allow the development of high-performance hematite photoanodes.

Ceria supported ruthenium(0) nanoparticles: Highly efficient catalysts in oxygen evolution reaction

Ruthenium(0) nanoparticles were successfully prepared on the surface of ceria (Ru0/CeO2) and used as catalysts on glassy carbon electrode (GCE) in oxygen evolution reaction (OER) from water electrolysis at room temperature. Ru0/CeO2 on GCE exhibits high catalytic activity for OER in alkaline solution. It provides a low onset potential of 1.57 V vs. RHE and low overpotential of 420 mV vs. RHE to reach a current density of 10 mA cm−2. Ru0/CeO2 on GCE shows no change in the onset potential value even after 6.1 h electrochemical measurement in OER.

Synergistic impact of Ni–Cu hybrid oxides deposited on ordered mesoporous carbon scaffolds as non-noble catalyst for methanol oxidation

Non-conventional soft-template method was deployed in synthesizing high surface area, ordered mesoporous carbon (OMC). Ordered mesoporous framework was confirmed from the collective data derived from XRD, N2 sorption and HR-TEM analyses. 15 wt% of variant compositions of Ni:Cu viz., 3:1, 1:1, 1:3 and pristine nickel and copper were deposited onto the OMC by using NaBH4 as a reductant and cetyltrimethylammonium bromide as capping agent. The effect of the reductant in the formation of a particular metal phase was well comprehended from the high angle XRD patterns; the reduction in surface area of the support after metal deposition was taken into account from the N2 sorption analysis. SEM–EDX and HR-TEM–EDX techniques were useful in quantifying the wt% of the deposited metals. The redox properties, charge transfer resistance and stability of all the catalysts toward methanol oxidation were characterized via cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry, respectively. Among all the tested samples, high specific surface area (436 m2 g−1), highest current density (182.07 mA cm−2), least onset potential (0.34 V) and charge transfer resistance (Rct) value of 0.355 Ω with 87.68% retention in current density over 7200 s were achieved when Ni and Cu were mixed in equal weight% to give NiCu hybrid oxides@OMC electrocatalyst.

Hierarchical Flowerlike Highly Synergistic Three-Dimensional Iron Tungsten Oxide Nanostructure-Anchored Nitrogen-Doped Graphene as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction.

A unique and novel structural morphology with high specific surface area, highly synergistic, remarkable porous conductive networks with outstanding catalytic performance, and durability of oxygen reduction electrocatalyst are typical promising properties in fuel cell application; however, exploring and interpreting this fundamental topic is still a challenging task in the whole world. Herein, we have demonstrated a simple and inexpensive synthesis strategy to design three-dimensional (3D) iron tungsten oxide nanoflower-anchored nitrogen-doped graphene (3D Fe-WO3 NF/NG) hybrid for a highly efficient synergistic catalyst for oxygen reduction reaction (ORR). The construction of flowerlike Fe-WO3 nanostructures, based on synthesis parameters, and their ORR performances are systematically investigated. Although pristine 3D Fe-WO3 NF or reduced graphene oxides show poor catalytic performance and even their hybrid shows unsatisfactory results, impressively, the excellent ORR activity and its outstanding durability are further improved by N doping, especially due to pyridinic and graphitic nitrogen moieties into a graphene sheet. Remarkably, 3D Fe-WO3 NF/NG hybrid nanoarchitecture reveals an outstanding electrocatalytic performance with a remarkable onset potential value (∼0.98 V), a half-wave potential (∼0.85 V) versus relative hydrogen electrode, significant methanol tolerance, and extraordinary durability of ∼95% current retention, even after 15 000 potential cycles, which is superior to a commercial Pt/C. The exclusive porous architecture, excellent electrical conductivity, and the high synergistic interaction between 3D Fe-WO3 NF and NG sheets are the beneficial phenomena for such admirable catalytic performance. Therefore, this finding endows design of a highly efficient and durable nonprecious metal-based electrocatalyst for high-performance ORR in alkaline media.

Morphological Ensembles of N‐Doped Porous Carbon Derived from ZIF‐8/Fe‐Graphene Nanocomposites: Processing and Electrocatalytic Studies

AbstractEngineering the active site density of porous carbon catalysts for enhanced electrocatalytic activity is the current focus in the quest for economically viable fuel cells. Herein, we synthesise ZIF‐8/Fe‐graphene composites for the formation of N and Fe co‐doped carbon with diverse morphologies ranging from tubes and sheets to frameworks of carbon. A synthetic strategy involving the one pot synthesis of ZIF‐8 based composites is accomplished by the reaction of 2‐methylimidazole with mixed Zn/Fe salt solution containing graphene dispersions. The high temperature heat treatment of this precursor mix yielded micro‐meso porous architectures of N, Fe co‐doped carbon with dispersions of Fe/Fe3C. An onset potential value of 0.95 V and a half‐wave potential of 0.82 V coupled with excellent durability and stability in alkaline medium indicated improved electrocatalytic performances over its commercial Pt/C counterpart. The appreciable electrocatalytic properties of the synthesized carbon are attributed to its morphological diversity, hybrid structure, high N doping and its heteroporous characteristics. The dispersed Fe/Fe3C and FeNx sites facilitated enhanced oxygen adsorption and the graphene inclusions in the composite provided retention of high nitrogen contents.