Aditi Halder

Efficient Solar Energy Conversion Using CaCu3Ti4O12 Photoanode for Photocatalysis and Photoelectrocatalysis

A highly efficient third generation catalyst, CaCu3Ti4O12 (CCTO) shows excellent photoelectrochemical (PEC) and photocatalytic ability. As only 4% part of the solar spectrum covers UV light, thus it is highly desirable to develop visible light active photocatalyst materials like CCTO for effective solar energy conversion. A direct band transition with a narrow band gap (1.5 eV) was observed. Under light irradiation, high photocurrent density was found to be 0.96 mA/cm2, indicating the visible light induced photocatalytic ability of CCTO. Visible light mediated photocatalytic and photoelectrocatalytic degradation efficiency of CaCu3Ti4O12 pellets (CCTO) was investigated for three classes of pharmaceutical waste: erythrosin (dye), ciprofloxacin (antibiotic) and estriol (steroid). It is found that the degradation process follows first order kinetic reaction in electrocatalysis, photocatalysis and photoelectrocatalysis and high kinetic rate constant was observed in photoelectrocatalysis. This was quite high in comparison to previously reported methods.

Efficient Electron Transfer across ZnO-MoS2-RGO Heterojunction for Remarkably Enhanced Sunlight Driven Photocatalytic Hydrogen Evolution

The development of noble metal-free catalysts for hydrogen evolution is required for energy applications. In this regard, ternary heterojunction nanocomposites consisting of ZnO nanoparticles anchored on MoS2 -RGO (RGO=reduced graphene oxide) nanosheets as heterogeneous catalysts show highly efficient photocatalytic H2 evolution. In the photocatalytic process, the catalyst dispersed in an electrolytic solution (S2- and SO32- ions) exhibits an enhanced rate of H2 evolution, and optimization experiments reveal that ZnO with 4.0 wt % of MoS2 -RGO nanosheets gives the highest photocatalytic H2 production of 28.616 mmol h-1  gcat-1 under sunlight irradiation; approximately 56 times higher than that on bare ZnO and several times higher than those of other ternary photocatalysts. The superior catalytic activity can be attributed to the in situ generation of ZnS, which leads to improved interfacial charge transfer to the MoS2 cocatalyst and RGO, which has plenty of active sites available for photocatalytic reactions. Recycling experiments also proved the stability of the optimized photocatalyst. In addition, the ternary nanocomposite displayed multifunctional properties for hydrogen evolution activity under electrocatalytic and photoelectrocatalytic conditions owing to the high electrode-electrolyte contact area. Thus, the present work provides very useful insights for the development of inexpensive, multifunctional catalysts without noble metal loading to achieve a high rate of H2 generation.

Enhanced electrocatalytic performance of perovskite supported iron oxide nanoparticles for oxygen reduction reaction

Perovskite oxide based materials have drawn considerable amount of attention as non-precious, non-noble cathode catalysts in oxygen reduction reactions for fuel cell and battery applications. High efficiency of perovskite catalysts often suffers due to instability and poor conductivity issues. Thus, the integration of these perovskite materials with other active catalysts is be of great interest. In this article, a series of new nanocomposites of perovskite–iron oxide with different molar ratios has been developed by hydrothermal method. We have shown that double perovskite calcium copper titanate CaCu3Ti4O12 (CCTO) supported iron oxide (Fe2O3) catalysts exhibit excellent activity as cathode catalyst for oxygen reduction reactions in fuel cells. Three different composites of CaCu3Ti4O12 (CCTO) with Fe2O3 were prepared and the composites were analysed by various structural and microstructural characterization methods, such as XRD and FESEM. Microstructural investigations revealed cubic shaped iron oxide nanoparticles decorated over CCTO particles. Electrochemical analysis showed that the performance of composites improved drastically with increase in the amount of CCTO. Kinetic studies by rotating ring disc electrode method revealed that the composites exhibit four electron pathway for oxygen reduction reaction and generate hydrogen peroxide as an intermediate. This work demonstrates a new type of efficient metal oxide–perovskite composite for oxygen redution catalysis.

Ferroelectric electrocatalysts: a new class of materials for oxygen evolution reaction with synergistic effect of ferroelectric polarization

AbstractWe exploit the role of the remnant polarization to improve the electrocatalytic performance of ferroelectric perovskite. We report cost-effective, noble metal-free, ferroelectric electrocatalyst Bi0.5Na0.5TiO3 and the effect of remnant polarization on oxygen evolution reaction involved in alkaline fuel cells. The forward poling decreases the Tafel slope from 85 mv/decade to 39 mv/decade and also increases the mass activity by threefold. The effect of polarization on flat-band potential and the Schottky barrier between electrode and electrolyte contributes to enhanced electrochemical activity.

A Polycarboxyl-Decorated FeIII-Based Xerogel-Derived Multifunctional Composite (Fe3O4/Fe/C) as an Efficient Electrode Material towards Oxygen Reduction Reaction and Supercapacitor Application

Low cost, non-noble metal catalysts with a good oxygen reduction reaction (ORR) activity comparable to that of platinum and also having good energy storage properties are highly desirable but challenging. Several challenges are associated with the development of such materials. Herein, we demonstrate a new polycarboxyl-functionalised FeIII -based gel material, synthesised following a solvothermal method and the development of its composite (Fe3 O4 /Fe/C) by annealing at optimised temperature. The developed composite displayed excellent electrocatalytic activity for the oxygen reduction reaction with an onset potential of 0.87 V (vs. RHE) and a current density value of -5 mA cm-2 , which are comparable with commercial 20 wt % Pt/C. In addition, as one of the most desirable properties, the composite exhibits a better methanol tolerance and greater durability than Pt/C. The same material was explored as an energy storage material for supercapacitors, which showed a specific capacitance of 245 F g-1 at a current density of 1 A g-1 . It is expected that this Fe3 O4 /Fe/C composite with a disordered graphitised carbon matrix will pave a horizon for developing energy conversion and energy storage devices.

A dysprosium-based new coordination polymer and its activity towards the oxygen reduction reaction

A new dysprosium-based coordination polymer (Dy-CP) was synthesized by the solvothermal method and studied for ORR catalysis. The catalytically active Dy2O3 on graphitized carbon was synthesized from this particular Dy-CP via annealing. Generally, MOFs containing transition elements, such as Zn, Fe, and Co, have been studied for ORR, and they show very good activity as ORR catalysts. Although lanthanide-based perovskites have also been explored for ORR, lanthanide-based MOF/CPs have not been evaluated for the same. The promising activities of other transition metal-based oxides inspired us to study the ORR activity of the dysprosium-based CP. As a precursor molecule for porous nanocarbon synthesis, this Dy-based CP was graphitized under particular annealing conditions and its influence on the ORR activity was investigated.