La0.80Sr0.20CoO3 as a noble-metal-free catalyst for the direct oxidation of formic acid under zero applied potential

Direct oxidation of formic acid to CO2 using noble-metal-free La0.80Sr0.20CoO3 is demonstrated in this study. The catalyst was able to oxidize HCOOH without any externally applied potential. The activity of La0.80Sr0.20CoO3 is compared with that of Pt nanoparticles. It is observed that the amount of CO2 generated using La0.80Sr0.20CoO3 is five times higher than that generated with Pt nanoparticles. The experimental observations are supported by DFT calculations, which reveal the role of the lattice oxygen in La0.80Sr0.20CoO3 in the catalytic effect. The Sr ions were not found to have any appreciable role in the dissociation step. Weak binding of CO2 involving energy changes of the order of ?1?kcal/mol indicated the ease of CO2 desorption from the catalyst surface, thus making the catalyst highly active for electrochemical HCOOH oxidation.by Anuj Bisht Phanikumar Pentyala, Parag A.Deshpande and Sudhanshu Sharm

Dry reforming activity due to ionic Ru in La1.99Ru0.01O3: the role of specific carbonates

Dry reforming of methane was carried out over La2?2xRu2xO3 (x = 0.005, 0.01). Substitution of just 0.5 atom% of Ru in La2O3 enhanced the activity by 20 times in terms of conversion when compared to the activity exhibited by La2O3. The oxygen storage capacity of the Ru doped sample was considerably higher than undoped La2O3, which resulted in higher conversions of CH4 and CO2. The measured conversion of CH4 and CO2 was 72 and 80%, respectively, at 850 �C. The same was merely 4% with La2O3 under the same experimental conditions. DRIFTS studies demonstrated the role of a specific type of carbonates in promoting the activity of the catalyst. DFT calculations provided the rationale behind the selection of the Ru-in-La2O3 methane dry reforming catalyst. The surface structures of the pure and Ru-substituted compounds were determined, corroborating the experimental observation of enhanced oxygen storage capacity on Ru substitution. Different active surface oxygen species were identified and their roles in improving reducibilities and improving reactivities were established. The experimentally observed surface carbonate species were also identified using calculations. The combined experiment + calculation approach proved ionic Ru in La2?2xRu2xO3 to be a novel and efficient dry reforming catalyst.by Bhanu P. Gangwar, Phanikumar Pentyala, Khushubo Tiwari, Krishanu Biswas, Sudhanshu Sharma and Parag A. Deshpand

Nanocoral CuCo2S4 thiospinels: Oxygen evolution reaction via redox interaction of metal ions

Understanding the electrocatalytic activity and redox mechanism in mixed metal sulfides has steered the present work. Mixed metal sulfide, CuCo2S4, synthesised by hydrothermal method, reveals the presence of highly crystalline nanocoral sheets of CuCo2S4 with mixed oxidation states of Co and Cu ions. Electrochemical measurements show superior oxygen evolution reaction (OER) activity and high exchange current density over CuCo2S4 in comparison with pristine (Co3S4 and Cu2S) and sintered CuCo2S4. In 0.5 M KOH, the nanocoral CuCo2S4 catalyst and its sintered form show a current density of 10 mA cm−2 at overpotential of 368 mV and 511 mV, respectively. A close inspection of the electrocatalytic performance in correlation with XPS spectra reveals the synergistic effect of Co and Cu ions through a redox interaction. Density Functional Theory calculations also indicate strong dependence of redox activity on redox couples as accompanied with changes in the partial charges of different constituent ions in the catalyst upon adsorption of hydroxyl ions which is a key step in OER. The study not only details sulfide-based catalytic compound for OER but also provides conclusive insights into the surface redox processes thereby providing an alternative direction to the search on novel OER catalysts.N.S. acknowledges DST Women in Science (WoS-A) program (SR/WOS-A/PM-35/2017(G)) for granting project. S.S. and S.N. gratefully acknowledge DST-SERB sponsored research project (EMR/2016/000806) for funding and fellowship. Authors are thankful to IIT Gandhinagar for CIF facility and VIT, Vellore for HR-TEM measurements.Peer reviewe