Subbiah Ravichandran

Novel cross-linked anion exchange membrane based on hexaminium functionalized poly(vinylbenzyl chloride)

Hydroxide anion exchange membranes (HAEMs) are of recent research interest, since these membranes can potentially replace the noble metal catalysts used in electrochemical energy conversion systems such as fuel cells and electrolysers. The conductivity and stability of state-of-the-art anion exchange membranes are far below those required for real applications. Herein, we report a novel anion exchange membrane based on aminated and cross-linked poly(vinylbenzyl chloride) prepared by an easy, viable synthetic route. β-Hydrogen free, multi-nitrogen containing ‘hexamethylenetetramine’ was used and explored as an amination/cross-linking agent for the first time in this study. FT-IR and 1H-NMR analysis results confirmed the successful quaternization of poly(vinylbenzyl chloride) with hexamine. TGA results showed the degradation temperature of the quaternized polymer is as high as 160 °C. AFM analysis revealed that the membrane possesses phase separated morphology with hydrophobic and hydrophilic domains. The ionic conductivity of the membranes increased when the amine to polymer ratio was increased from 0.2 to 0.33, and the highest ionic conductivity achieved was 6.8 × 10−3 S cm−1. The membrane has good chemical and alkaline stability which strongly suggests that the membrane would be a promising material for electrochemical energy conversion systems.

Fabrication of spinel ferrite based alkaline anion exchange membrane water electrolysers for hydrogen production

Alkaline anion exchange membrane water electrolysis (AEMWE) is considered to be an alternative to proton exchange membrane water electrolysis (PEMWE), owing to the use of non-noble meta/metal oxides in AEMWE. Here, we report a highly durable and low-cost AEM-based electrolysis cell with active spinel ferrite catalysts for hydrogen production. Ce-substituted MnFe2O4 was synthesized by a combustion method and investigated as the electro catalyst for oxygen evolution reaction (OER). Substitution of Ce in the cubic lattice of MnFe2O4 increases the conductivity of CexMnFe(2−x)O4, which results in a negative shift in the OER onset potential. At 25 °C, the single cell with Ce0.2MnFe1.8O4 exhibited a current density of 300 mA cm−2 at 1.8 V. Notably, Ce0.2MnFe1.8O4 demonstrates a durability of >100 hours in continuous electrolysis.

Enhancing the electro catalytic activity of manganese ferrite through cerium substitution for oxygen evolution in KOH solutions

Alkaline water electrolysis (AWE) is the simplest way of producing hydrogen, an attractive fuel for the future. In view of their cost-effectiveness and durability, non-noble metal oxides are promising catalysts for AWE. Here, we studied the effect of Ce substitution on the OER activity of manganese ferrite. Ce substituted MnFe2O4 (0 ≤ x ≤ 0.8) was synthesized by a combustion method. Characterization techniques such as SEM, XRD, EDAX and XPS were used to analyse the surface morphology and the chemical composition of CexMnFe2−xO4. Substitution of Ce3+ in the cubic lattice of MnFe2O4 increases the conductivity of CexMnFe2−xO4, which results in the negative shift in the OER onset potential. Among all the Ce3+ substituted manganese ferrites, Ce0.2MnFe1.8O4 was found to be more active for OER in terms of current and stability. Notably, Ce0.2MnFe1.8O4 affords a current density of 10 mA cm−2 at a small overpotential of ∼310 mV and a Tafel slope value of 31 mV per decade, these values are comparable to the well-investigated non-noble metal oxides.

One-step synthesis of boron nitride carbon nanosheets containing zinc oxide for catalysis of the oxygen reduction reaction and degradation of organic dyes

Boron nitride carbon nanosheets containing zinc oxide (ZnO/h-BNC) with a hexagonal B–N bond structure were prepared using a scalable, one-step process involving the thermal treatment of glycine, zinc nitrate, graphene oxide and boron oxide. The as-prepared ZnO/h-BNC hybrids were active for both the electrocatalytic reduction of oxygen under alkaline conditions and the photocatalytic oxidation of methyl orange dye. The ZnO/h-BNC nanosheets showed a much improved onset potential and reduced current density compared with ZnO/BCN sheets with a dominant CN bond configuration for the oxygen reduction reaction (ORR). The BNC enriched with h-BN showed an excellent ORR performance, whereas the CN dominant BCN showed relatively less activity for the ORR, suggesting an intrinsic difference in properties of the BCN-based materials with different bond configurations. The Zn species located inside the h-BNC matrix acted as photocatalytically active centres for the degradation of methyl orange dye under UV irradiation.

Eco-friendly and facilely prepared silica modified amorphous titania (TiO2–SiO2) electrocatalyst for the O2 and H2 evolution reactions

An eco-friendly silica modified amorphous titania (TiO2–SiO2) electrocatalyst is prepared. This silica modified amorphous titania (TiO2–SiO2) composite material is prepared by facile spurting of silica (obtained from a sustainable resource) over a titanium plate and identified as an active electrocatalyst for O2 and H2 evolution by water oxidation. The prepared composite shows a maximum current density of 12 mA cm−2 at 2 V (versus RHE) in 1 M KOH electrolyte. This is because the semiconductor heterostructure of the structurally and chemically dissimilar amorphous TiO2–SiO2 composite introduces new collective electronic states with improved electrical conductivity, with a decrease in the work function. The catalytic activity is found to be stable in continuous operation for about 10 h. The physicochemical characterization of the electrocatalyst was carried out using scanning electron microscopy, energy dispersive X-rays, X-ray diffraction, X-ray photoelectron spectra, and electron paramagnetic resonance and the work function was examined by a Scanning Kelvin Probe. Because of the simple, cheap, and scalable preparation procedure, the electrocatalyst is highly promising for practical low cost and high technology applications. Interestingly, the system is active in the oxygen and hydrogen evolution reactions, leading to a promising bifunctional electrocatalyst.

Sulfonated Polystyrene-Block-(Ethylene-Ran-Butylene)-Block-Polystyrene (SPSEBS) Membrane for Sea Water Electrolysis to Generate Hydrogen

Sea water oxidation is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis poisonous chlorine evolution is the most favored reaction over oxygen evolution at the anode. In this work, study has been focused on the development of electrode materials with high selectivity for oxygen evolution reaction over chlorine evolution. We employed perm selective membrane i.e. sulfonated polystyrene-block-(ethylene-ran-butylene)-block-polystyrene (SPSEBS) which electrostaticlly repels the chloride ion (Cl-) to the electrode surface and thereby enhances the oxygen evolution and reduces the chlorine evolution at the anode. The electrochemical behavior of both modified and bare IrO2 electrodes were characterized using polarization studies and the gas evolution efficiencies are calculated based on bulk electrolysis method. The surface morphology of the electrode was analyzed before and after electrolysis using scanning electron microscope (SEM). The results suggest that the nearly 95% oxygen evolution efficiency could be achieved when the surface of IrO2/Ti electrode was modified with perm selective membrane.