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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]

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]

• Tetraethyl orthosilicate and dopamine employed to produce N-doped mesoporous carbon sheet. • NCS-1.0 with optimum loading renders high density of (DA) 2 -dihydroxyindole trimer product. • The carrier concentration and flat band potential altered hugely by the pyridinic-N content. • Excellent catalytic performance of NCS-1.0 is attributed to its high mesoporous surface area, high percentage of pyridinic and graphitic-N content. In this work, a simple and innovative method is explored to achieve high surface area with substantial mesoporosity by utilizing tetraethyl orthosilicate and dopamine (DA) precursors. The initial step leads to silica/polydopamine (PDA) composite which undergoes a carbonization, and silica etching yields the desired carbon. Our examination confirms the non-covalent interaction in (DA) 2 -dihydroxyindole (DHI) trimer leads to N-doped mesoporous carbon sheet (NCS)-1.0 with large surface area (1068 m2 g −1), high pore volume (0.706 cm3 g −1) and layer thickness of 43 nm. NCS-1.0 offers excessive graphitic, pyridinic N sites thereby resulting in an awesome oxygen reduction reaction (ORR) activity. Remarkably, it demonstrates a positive onset potential of 0.88 V, current density of 4.3 mA cm−2, the carrier concentration of 1.27 × 1016 cm−3, and flat band potential of 0.45 V. Such combination of both physical and electrochemical factors of NCS-1.0 favours the four-electron pathway, excellent methanol tolerance with long term stability. [Display omitted] [ABSTRACT FROM AUTHOR]

Transition metal oxide based materials are believed as a sustainable and effective electrocatalysts for oxygen evolution and oxygen reduction reactions (OER/ORR). However, poor conductivity, specific surface area, and tunable crystallography are major bottlenecks. To alleviate such issues, we developed a highly active spinel Co 3 O 4 decorated N-doped hollow carbon sphere (Co 3 O 4 /NHCS) by single step decoration using cobalt phthalocyanine (CoPc) precursor for the first time. The introduction of various extents of CoPc significantly affects the sphere wall thickness, defect sites, doping amount of cobalt content, and the concentration of Co3+ and Co2+ sites. The resulting optimum loading of 0.2 g of Co 3 O 4 /NHCS-0.2, exhibits a highly uniform hollow carbon sphere with a high wall thickness (61 nm), better surface area (445 m2 g−1), and moderate defect sites. Notably, an exterior concentration of octahedral Co3+ (35.50%) and tetrahedral Co2+ (26.54%) sites serve as the active centres for OER and ORR, respectively. Remarkably, the obtained material exhibits exceptional OER performance with a potential of 1.80 V vs. RHE in 0.1 M KOH medium for achieving a current density of 10 mA cm−2, outperforming the benchmark RuO 2 material. In addition, Co 3 O 4 /NHCS-0.2 demonstrates an impressive ORR electrocatalytic activity with onset potential of 0.89 V vs. RHE, excellent current density of 5.0 mA cm−2, lower Tafel slope of 60 mV dec−1 and close to four electron transfer. Moreover, the moderate carrier concentration, flat band potential, higher tetrahedral Co2+ and pyridinic N sites significantly improved the ORR activity and methanol oxidation tolerance ability. [Display omitted] • Co 3 O 4 decorated N-doped hollow carbon sphere by single step process. • The 0.2 g of cobalt phthalocyanine shows the higher Co3+/Co2+ ratio. • Co 3 O 4 /NHCS-0.2 possesses a remarkable OER activity. • Co 3 O 4 /NHCS-0.2 demonstrates an impressive ORR activity. [ABSTRACT FROM AUTHOR]