Indrajit Shown

Highly Efficient Visible Light Photocatalytic Reduction of CO2 to Hydrocarbon Fuels by Cu-Nanoparticle Decorated Graphene Oxide

The production of renewable solar fuel through CO2 photoreduction, namely artificial photosynthesis, has gained tremendous attention in recent times due to the limited availability of fossil-fuel resources and global climate change caused by rising anthropogenic CO2 in the atmosphere. In this study, graphene oxide (GO) decorated with copper nanoparticles (Cu-NPs), hereafter referred to as Cu/GO, has been used to enhance photocatalytic CO2 reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (∼4-5 nm in size) in the GO hybrid are shown to significantly enhance the photocatalytic activity of GO, primarily through the suppression of electron-hole pair recombination, further reduction of GOs bandgap, and modification of its work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. A strong interaction is observed between the metal content of the Cu/GO hybrids and the rates of formation and selectivity of the products. A factor of greater than 60 times enhancement in CO2 to fuel catalytic efficiency has been demonstrated using Cu/GO-2 (10 wt % Cu) compared with that using pristine GO.

A nontoxic solvent based sol–gel Cu2ZnSnS4 thin film for high efficiency and scalable low-cost photovoltaic cells

A non-toxic sol–gel spin coating approach is one of the attractive routes to achieve high atom economy, good quality Cu2ZnSnS4 (CZTS) thin films. In this paper, we introduce 1,3-dimethyl-2-imadazolidinone as a solvent for the preparation of highly viscous, homogeneous, nontoxic CZTS ink that eliminates the need for the use of additional binders or additives to disperse the precursors. In addition, we further report the annealing of the spin coated CZTS thin film in 6% diluted H2S gas with an externally supplied tin and sulfur environment to suppress the loss of tin from the thin-film surface and to enhance the device performance. CZTS grain sizes greater than 0.7 μm have been achieved with no detectable presence of carbon rich layers or layers containing fine grain sizes at the Mo/CZTS interface. An efficiency of 5.67% for the champion device fabricated here has been achieved with an open circuit voltage of 0.58 V, a short current density of 18.48 mA cm−2, and a fill factor of 53.14%.

Directly-Grown Hierarchical Carbon Nanotube@Polypyrrole Core–Shell Hybrid for High-Performance Flexible Supercapacitors

A hierarchical carbon nanotube-polypyrrole (CNT-PPy) core-shell composite was fabricated by growing CNTs directly on carbon cloth (CC) as a skeleton followed by electropolymerization of PPy with controlled polymerization time. Direct fabrication of electroactive (CNT-PPy) materials on the flexible CC electrode could reduce the interfacial resistance between the electrode and electrolyte and improve the ion diffusion. The supercapacitor electrode based on optimized PPy/CNT-CC exhibits excellent electrochemical performance, with the highest gravimetric capacitance being roughly 1038 F g(-1) per active mass of PPy and up to 486.1 F g(-1) per active mass of the PPy/CNT composite. Notably, excellent flexibility and cycle stability up to 10 000 cycles with only 18 % capacitance loss was achieved. At the same time, the fabricated asymmetric supercapacitor (PPy/CNT-CC∥CNT-CC) shows the maximum power density of 10 962 W kg(-1) at an energy density of 3.9 Wh kg(-1) under the operating potential of 1.4 V. The overall high cycle stability and high performance of the fabricated PPy/CNT-CC flexible electrode is due to the novel binder-free direct growth process.

High-performance pyrolyzed iron corrole as a potential non-precious metal catalyst for PEMFCs

This work demonstrates the performance of carbon black-supported pyrolyzed Fe–corrole (py-Fe–corrole/C) as a cathode catalyst for the oxygen reduction reaction (ORR) in PEMFCs. The ORR measurements reveal that the py-Fe–corrole/C exhibits good ORR activity, via the direct four-electron reduction pathway, in the reduction of O2 to H2O. The H2–O2 PEMFC produces high activity and good stability. The enhanced ORR activity is attributable to the network structure of poly-aromatic hydrocarbons, the quaternary (graphitic)-type nitrogen and the coordination structure of the py-Fe–corrole/C. Square wave voltammetry has been applied to the py-Fe–corrole/C to perform a redox reaction of Fe(II)/Fe(III) at 0.6 V. Finally, detailed in situ X-ray adsorption spectroscopy has been applied to determine the ORR mechanism of py-Fe–corrole/C.

Ni‐Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction

One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO2 molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni-nanocluster loaded black TiO2 (Ni/TiO2[Vo] ) with built-in dual active sites for selective photocatalytic CO2 conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO2 binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.

Hybrid bimetallic-N4 electrocatalyst derived from a pyrolyzed ferrocene–Co-corrole complex for oxygen reduction reaction

A bimetallic macrocyclic-N4 complex, FCC, consisting of a Co-corrole core equipped with a peripheral ferrocene has been synthesized. The complex structure was thoroughly characterized using single crystal X-ray diffraction. The Co-corrole, mono-substituted with a peripheral Fe-complex, exhibited unique characteristics after its pyrolysis for oxygen reduction reaction (ORR) activity. Carbon black supported FCC, pyrolyzed at 500 °C, gives an electrocatalyst with a bimetallic (Co and Fe) active center, which facilitates ORR via a 4-electron pathway. The new non-precious bimetallic electrocatalyst exhibits a high electron transfer number of more than 3.95, with a H2O2 yield of below 2.3%, over the potential range of 0.2–0.8 V for ORR in acidic medium, which is superior to pyrolyzed Co-corroles. The enhanced ORR activity for the catalyst derived from this technique provides a new prospect for next-generation non-precious N4 electrocatalysts for fuel cell applications.