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The dual heteroatom doped mesoporous carbon (MC) is an excellent substitute for platinum‐based catalyst in cathodic oxygen reduction reaction (ORR) of fuel cells. In this work, nitrogen (N) as the primary heteroatom doping, phosphorus (P), boron (B), and sulfur (S) as the secondary heteroatom doping are introduced in the MC framework. Santa barbara amorphous (SBA‐15) employed as the supporting material to investigate the secondary heteroatom doping effect on MC towards ORR performance. Compared with B and S doping, the P doping modifies the charge delocalization in the MC structure. In addition, it enhances the surface area (971 m2/g), defect sites (1.18), high pyridinic (28.72 %) and high graphitic content (44.42 %) thereby facilitated the remarkable ORR activity. Moreover, electrochemical studies proved that N and P dual doped mesoporous carbon (NPMC) has a better carrier concentration (5.58×1015 cm−3) and higher flat band potential (0.548 V vs RHE) which is confirmed by the Mott‐Schottky analysis. Further, ORR studies demonstrated that NPMC material exhibited more positive onset potential (0.86 V), two‐electron pathway, lower Tafel slope (63 mV/dec) as well as Rct (11 Ω/cm2). In addition, the resultant material is found to be highly active towards ORR with excellent methanol tolerance and stability. [ABSTRACT FROM AUTHOR]

In this scientific work, a precipitation method is followed for the synthesis of copper oxide (CuO), cobalt oxide (Co3O4) and copper cobaltite (CuCo2O4) and the viability of using these materials as electrode modifiers has been studied. A sensitive electrochemical sensor for the determination of hydroxylamine has been introduced. The morphology and physical properties of the as synthesized materials were characterized with several characterization tools. It is found that the morphology and size of CuO, Co3O4 and CuCo2O4 are nanoflakes (300–350 nm), nanoplatelet (75–100 nm) and nanobricks (20–45 nm), respectively. In addition, CuO, Co3O4 and CuCo2O4 oxidize hydroxylamine at 0.57 V, 0.53 V and 0.44 V, respectively. Electrocatalytic oxidation current of hydroxylamine was proportional to the concentration of hydroxylamine in the range 0.075 to 8.25 mM. Also, under optimized condition, limit of detection and sensitivity in the DPV measurement are 0.65 μM ± 0.05 μM and 13.1 μA cm−2 mM−1, respectively. Hence, the proposed sensor is highly sensitive, selective, simple, precise and stable for hydroxylamine detection in the real water samples. [ABSTRACT FROM AUTHOR]

Ordered mesoporous carbon (OMC) is a promising material for oxygen reduction reaction (ORR) in fuel cells owing to its high surface area and more number of catalytic active sites. Herein, OMC was synthesized by hard template method, i. e., nanocasting of sacrificial silica template (SBA‐15) and then the sacrificial template was abolished using three different etching chemicals namely, hydrofluoric acid (HF), sodium hydroxide (NaOH) and polyvinylidene fluoride (PVDF) respectively, in order to study the etching effect. The etched OMCs derived from the SBA‐15 template was confirmed by various characterization techniques. In OMC, the porous nature, surface morphology and defect density changes with respect to etching chemicals were evidently determined. From the electrochemical studies, it has been concluded that the NaOH etched OMC showed higher electrocatalytic activity than others by exhibiting more positive onset (0.83 V), half‐wave potential (0.75 V), high current density (3.3 mA/cm2), Tafel slope (83 mV/dec) and n‐value (2.4). Eventually, the electrochemical impedance study (EIS) was performed to determine the charge transfer resistance (Rct) of various etched OMCs and has been found that NaOH etched OMC shows the lowest Rct value due to the presence of more defective sites and result in enhancing oxygen adsorption during ORR. Ordered mesoporous carbons (OMCs) is a promising electrocatalyst for ORR in fuel cells owing to its surface area and active sites. Here, OMCs were synthesized by using silica template (SBA‐15) then the template is removed by three different etching agents such as HF, NaOH and PVDF (polyvinylidene fluoride). The porosity, morphology and surface functional groups changes with respect to etching chemicals. Further, the electrochemical studies concluded that the NaOH etched OMC showed better activity than others. [ABSTRACT FROM AUTHOR]

In this work, a hard‐template‐based nano‐replication process is employed to prepare mesoporous MnO2 materials. We adopted four silica materials, namely, SBA‐15, KIT‐6, MCM‐41, and MCM‐48 as templates to prepare MnO2 materials by using a nanocasting route. The structural characteristics of the resultant MnO2 materials were thoroughly investigated by using XRD, BET, FESEM, HR‐TEM, XPS, and Raman techniques. All studies confirmed the replication of porous MnO2 nanostructures from silica supports in β‐crystallographic form. By employing X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS), we identified the existence of Mn and oxygen vacancies in the developed MnO2 material. The hydrodynamic linear sweep voltammetric technique was employed to demonstrate the efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity of the catalyst in 0.1 M KOH solution. The KIT‐6‐derived MnO2 nanostructure displayed equal activity to the benchmark catalyst RuO2. This work lays a foundation to prepare and employ ordered mesoporous MnO2 materials as OER/ORR catalysts, which have potential applications in electrochemical energy conversion and storage devices. Bifunctional catalysts: Mesoporous MnO2 materials are obtained from a hard‐template‐based nanocasting method. SBA‐15, KIT‐6, MCM‐41, and MCM‐48 are selected as (2D and 3D) templates. The replication of porous MnO2 nanostructures from silica supports yields the β‐crystallographic form. X‐ray absorption studies identify the existence of Mn and oxygen vacancies in the materials. Electrochemical studies demonstrate efficient oxygen evolution and oxygen reduction reaction activity of the resultant materials. 3D MnO2 displays an activity comparable to the benchmark RuO2 catalyst. [ABSTRACT FROM AUTHOR]

Non precious highly ordered mesoporous carbon (OMC) is of indomitable and perennial catalyst in fuel cells owing to their unique traits and abundant sources. The OMC has been synthesized using KIT‐6 sacrificial template and then this removed by three different etching agents, viz, hydrofluoric acid (HF), sodium hydroxide (NaOH) and polyvinylidene fluoride (PVDF). The principle aim of the present work is that to inspect the etched OMCs for oxygen reduction reaction (ORR) activity. In order to understand the effect of etching, we have first studied their fundamental properties. Among three, the HF etched OMC possess comparative surface area (234 m2 g‐1), mesoporous sizes (6 nm), large pore volumes (0.13 cm3 g‐1) and more accessible defective active sites (ID/IG = 0.90). Hence, the HF etched OMC replica manifest better ORR activity than others in terms of having (0.83 V) onset and (0.71 V) half wave potential, and (2.6 mA/cm2 at 0.2 V) current density in potassium hydroxide (KOH) electrolyte. From the Nyquist plot, a small semicircle (Rct = 13 Ω cm‐2) of HF etched OMC substantiates its better ORR activity. A comparative study on etching of OMC using different etching agents could guide to find out a suitable etching agent for modifying the surface properties of OMC. Ordered mesoporous carbons (OMCs) are of indomitable and perennial catalyst in fuel cells owing to their unique traits and abundant sources. The OMC has been synthesized using KIT‐6 template and then the template is removed by three different etching agents, viz, HF, NaOH and PVDF. The principle aim of the present work is to evaluate the etched OMCs towards ORR activity. The outcome of study identifies that HF etched OMC manifest better ORR activity than other etching agents. [ABSTRACT FROM AUTHOR]

A methodology has been developed for the estimation of intrinsic active area of Pt/C nano-catalysts which is crucial for the evaluation of catalyst's utilization in a membrane-electrode-assembly (MEA). The evaluation was carried out by employing the H-UPD and CO stripping methods for both a thin porous Pt/C-Nafion film coated on a glassy carbon disk and a carbon paper electrode. The results demonstrate that the measured values of intrinsic active area (i.e., the extents of utilization) of Pt/C in Nafion ionomer films are identical at both glassy carbon (GC) and carbon paper surfaces from 2 to 330 μg-Pt/cm2 loading. However, the measured active area is strongly dependent on the electrode support for the loadings greater than 330 μg-Pt /cm2 where the carbon paper electrodes show much higher active areas. Three different pre-activation methods have been adopted to activate all the Pt sites in the catalyst layer namely potential cycling and constant potential treatment at an applied potential of 0 or 1.2 V (RHE). These results demonstrate the necessity of such a simple and convenient pre-operation activation treatment for Pt/C catalysts in MEA to assess their intrinsic active area towards the electrochemical reactions. [ABSTRACT FROM AUTHOR]

The chemical state and formation mechanism of Pt-Ru nanoparticles (NPs) synthesized by using ethylene glycol (EG) as a reducing agent and their stability have been examined by in situ X-ray absorption spectroscopy (XAS) at the Pt LIII and Ru K edges. It appears that the reduction of Pt(IV) and Ru(III) precursor salts by EG is not a straightforward reaction but involves different intermediate steps. The pH control of the reaction mixture containing Pt(IV) and Ru(III) precursor salts in EG to 11 led to the reduction of Pt(IV) to Pt(II) corresponding to [PtCl4](2-) whereas Ru(III)Cl3 is changed to the [Ru(OH)6](3-) species. Refluxing the mixture containing [PtCl4](2-) and [Ru(OH)6](3-) species at 160 degrees C for 0.5 h produces Pt-Ru NPs as indicated by the presence of Pt and Ru in the first coordination shell of the respective metals. No change in XAS structural parameters is found when the reaction time is further increased, indicating that the Pt-Ru NPs formed are extremely stable and less prone to aggregation. XAS structural parameters suggest a Pt-rich core and a Ru-rich shell structure for the final Pt-Ru NPs. Due to the inherent advantages of the EG reduction method, the atomic distribution and alloying extent of Pt and Ru in the Pt-Ru NPs synthesized by the EG method are higher than those of the Pt-Ru/C NPs synthesized by a modified Watanabe method.