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Papers by Anand V Sankarraj
Langmuir, Jan 1, 2008
We report on the influence of a series of transition-metal-substituted Wells-Dawson (P 2 W 17 M n... more We report on the influence of a series of transition-metal-substituted Wells-Dawson (P 2 W 17 M n O 62 (12n)-; M ) W VI , Fe II , Co II , Ru II ) and Keggin (PW 12 O 40 3and PCoW 11 O 39 5-) anions on the oxygen reduction reaction (ORR) at Au, Pd, and Pt. Wells-Dawson POMs adsorbed on Au lead to large positive shifts of the ORR potential. The magnitude of the shift depends on the transition metal and is explained using a simple thermodynamic model. The best cathode performance was achieved using a PCoW 11 O 39 5cocatalyst and a Pt cathode. The +54 mV positive shift in the ORR potential that we observed is comparable to the performance of the best-known bimetallic catalysts.
Journal of the American …, Jan 1, 2004
Transition metal heteropolyanions have been used to catalyze a variety of organic oxidations but ... more Transition metal heteropolyanions have been used to catalyze a variety of organic oxidations but have not previously been used for O2 generation, despite sharing some structural similarities with dioxoruthenium water-oxidation catalysts. In this study, we report that the di-Ru-substituted polyoxometalate (POM) [Ru2Zn2(H2O)2(ZnW9O34)2]14- can be used to catalyze the electrochemical generation of O2. By comparing the behavior of this compound to that observed using a mono-Ru-substituted POM catalyst, we show that adjacent Ru sites are necessary to observe O2 generation. These observations suggest a reaction pathway involving two Ru-bound oxygen species combining to form O2 and are consistent with the accepted mechanism of electrochemical oxygen evolution. Finally, analysis of the observed electrode kinetics yields a Tafel slope of roughly 120 mV, which is similar to values reported previously for perovskite anodes.
Materials research …, Jan 1, 2000
A low temperature sol-gel technique was employed for the synthesis of vanadium substituted spinel... more A low temperature sol-gel technique was employed for the synthesis of vanadium substituted spinel of the type LiMn2−xVxO4 (x = 0.1 to 0.5). X-ray diffraction data indicates evidence for substitution of vanadium in the lattice. Particle size, FTIR, and differential thermal analyses were carried out on the samples. Charge–discharge characteristics of cells fabricated using these materials were studied. The cells were found to be stable for more than 20 cycles.
Pigment & Resin Technology, 2000
Pigment & resin …, Jan 1, 2000
Discusses the particulation of organic barrier layers, based on laboratory-bench data, obtained f... more Discusses the particulation of organic barrier layers, based on laboratory-bench data, obtained from the exposure of painted panels in low, high or neutral pH electrolytes. It also discusses their compatibility with the succeeding and preceding layers and the galvanic interactions at the layer substrate interfaces. Aspects like substrate effect, leaching of the micaceous iron powder, role of high temperature and hydrodynamic disturbances and distribution of ultrafine particulates have been highlighted using potential versus time plot, AAS data, and galvanic current measurements and XRD analysis. Exposure tests conducted under ambient conditions and under very strong hydrodynamic disturbances, revealed superior properties of the SiC particulated epoxy based barrier layers.
Conference Presentations by Anand V Sankarraj
Transition metal substituted polyoxometalates have been employed as oxygen reduction catalysts in... more Transition metal substituted polyoxometalates have been employed as oxygen reduction catalysts in the past decade. However, sandwich type polyoxometalates have very little representation in literature, save a couple of works in Fe and Cu substituted Wells Dawson polyoxometalate structures(1,2). In this work, substitution of some of the first-group transition metals V, Mn, Fe, Co, Ni, Cu & Zn together with Ru, Ir & Pd have been accomplished in a Weakley type sandwich polyoxometalate; {(WZnM2)[ZnW9O34]2}n-.These bimetallic-substituted polyoxometalates have been tested for electrocatalytic oxygen reduction in a pH=5 buffer solution (chosen due to stability issues of sandwich). There is a systematic trend in the position of oxygen reduction peak (E1/2) as a function of transition metal substitution. An attempt has been made to address the functionality of oxygen reduction peak to the thermodynamic redox potentials of the substituted transition metal. In this exercise, the central belt of transition metals is considered to be the electrocatalytic active site and the enveloping Keggin structures behave as electron transfer mediators.
Langmuir, Jan 1, 2008
We report on the influence of a series of transition-metal-substituted Wells-Dawson (P 2 W 17 M n... more We report on the influence of a series of transition-metal-substituted Wells-Dawson (P 2 W 17 M n O 62 (12n)-; M ) W VI , Fe II , Co II , Ru II ) and Keggin (PW 12 O 40 3and PCoW 11 O 39 5-) anions on the oxygen reduction reaction (ORR) at Au, Pd, and Pt. Wells-Dawson POMs adsorbed on Au lead to large positive shifts of the ORR potential. The magnitude of the shift depends on the transition metal and is explained using a simple thermodynamic model. The best cathode performance was achieved using a PCoW 11 O 39 5cocatalyst and a Pt cathode. The +54 mV positive shift in the ORR potential that we observed is comparable to the performance of the best-known bimetallic catalysts.
Journal of the American …, Jan 1, 2004
Transition metal heteropolyanions have been used to catalyze a variety of organic oxidations but ... more Transition metal heteropolyanions have been used to catalyze a variety of organic oxidations but have not previously been used for O2 generation, despite sharing some structural similarities with dioxoruthenium water-oxidation catalysts. In this study, we report that the di-Ru-substituted polyoxometalate (POM) [Ru2Zn2(H2O)2(ZnW9O34)2]14- can be used to catalyze the electrochemical generation of O2. By comparing the behavior of this compound to that observed using a mono-Ru-substituted POM catalyst, we show that adjacent Ru sites are necessary to observe O2 generation. These observations suggest a reaction pathway involving two Ru-bound oxygen species combining to form O2 and are consistent with the accepted mechanism of electrochemical oxygen evolution. Finally, analysis of the observed electrode kinetics yields a Tafel slope of roughly 120 mV, which is similar to values reported previously for perovskite anodes.
Materials research …, Jan 1, 2000
A low temperature sol-gel technique was employed for the synthesis of vanadium substituted spinel... more A low temperature sol-gel technique was employed for the synthesis of vanadium substituted spinel of the type LiMn2−xVxO4 (x = 0.1 to 0.5). X-ray diffraction data indicates evidence for substitution of vanadium in the lattice. Particle size, FTIR, and differential thermal analyses were carried out on the samples. Charge–discharge characteristics of cells fabricated using these materials were studied. The cells were found to be stable for more than 20 cycles.
Pigment & Resin Technology, 2000
Pigment & resin …, Jan 1, 2000
Discusses the particulation of organic barrier layers, based on laboratory-bench data, obtained f... more Discusses the particulation of organic barrier layers, based on laboratory-bench data, obtained from the exposure of painted panels in low, high or neutral pH electrolytes. It also discusses their compatibility with the succeeding and preceding layers and the galvanic interactions at the layer substrate interfaces. Aspects like substrate effect, leaching of the micaceous iron powder, role of high temperature and hydrodynamic disturbances and distribution of ultrafine particulates have been highlighted using potential versus time plot, AAS data, and galvanic current measurements and XRD analysis. Exposure tests conducted under ambient conditions and under very strong hydrodynamic disturbances, revealed superior properties of the SiC particulated epoxy based barrier layers.
Transition metal substituted polyoxometalates have been employed as oxygen reduction catalysts in... more Transition metal substituted polyoxometalates have been employed as oxygen reduction catalysts in the past decade. However, sandwich type polyoxometalates have very little representation in literature, save a couple of works in Fe and Cu substituted Wells Dawson polyoxometalate structures(1,2). In this work, substitution of some of the first-group transition metals V, Mn, Fe, Co, Ni, Cu & Zn together with Ru, Ir & Pd have been accomplished in a Weakley type sandwich polyoxometalate; {(WZnM2)[ZnW9O34]2}n-.These bimetallic-substituted polyoxometalates have been tested for electrocatalytic oxygen reduction in a pH=5 buffer solution (chosen due to stability issues of sandwich). There is a systematic trend in the position of oxygen reduction peak (E1/2) as a function of transition metal substitution. An attempt has been made to address the functionality of oxygen reduction peak to the thermodynamic redox potentials of the substituted transition metal. In this exercise, the central belt of transition metals is considered to be the electrocatalytic active site and the enveloping Keggin structures behave as electron transfer mediators.