Developing bio-inspired photosensitized hudrogen production and oxygen reduction catalyst

by Afsar Ali, Ab Qayoom Mir and Arnab Dutt

Inclusion of peripheral basic groups activates dormant cobalt-based molecular complex for catalytic H2 evolution in water

The protein scaffold plays a key role during the enzymatic catalysis for metalloenzymes. Here we have rationally designed an enzyme-inspired outer coordination sphere in the form of protic functionalities, such as natural amino acid derived carboxylic acid and phenolic ?OH groups, on the fringe of the cobalt-salen like complexes. This inclusion has enabled electrocatalytic H2evolution for an otherwise inactive cobalt-salen like core. The complexes containing peripheral carboxylic acid groups exhibited unique pH-switchable catalytic H2�production that is connected with the pKa�of the carboxylic acid group (?4.0), suggesting the crucial involvement of the carboxylate group during the catalytic activity. The one- and two-dimensional NMR results of the complexes have indicated the presence of a possible hydrogen bonding network, generated by those protic groups in aqueous solution. These results highlight that an inactive metal complex can be activated for specific small molecule activation via rational inclusion of outer coordination sphere functionalities.by Shikha Khandelwal, Afridi Zamader, Vivek Nagayach, Dependu Dolui, Ab Qayoom Mir and Arnab Dutt

Developing photosensitizer cobaloxime hybrids for solar-driven H2 production in aqueous aerobic conditions

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number of photoactive assemblies have emerged where a photosensitizer and cobaloxime-based H2 production catalysts work in tandem to convert light energy into the H-H chemical bonds. However, the long-term instability of these assemblies and the need for hazardous proton sources have limited their usage. Here, in this work, we have integrated a stilbene-based organic dye into the periphery of a cobaloxime core via a distinct axial pyridine linkage. This strategy allowed us to develop a photosensitizer-catalyst hybrid structure with the same molecular framework. In this article, we have explained the detailed procedure of the synthesis of this hybrid molecule in addition to its comprehensive chemical characterization. The structural and optical studies have exhibited an intense electronic interaction between the cobaloxime core and the organic photosensitizer. The cobaloxime was active for H2 production even in the presence of water as the proton source. Here, we have developed a simple airtight system connected with an online H2 detector for the investigation of the photocatalytic activity by this hybrid complex. This photosensitizer-catalyst dyad present in the experimental setup continuously produced H2 once it was exposed in the natural sunlight. This photocatalytic H2 production by the hybrid complex was observed in aqueous/organic mixture media in the presence of a sacrificial electron donor under complete aerobic conditions. Thus, this photocatalysis measurement system along with the photosensitizer-catalyst dyad provide valuable insight for the development of next generation photocatalytic H2 production devices.by Ab Qayoom Mir, Dependu Dolui, Shikha Khandelwal, Harshil Bhatt, Beena Kumari, Sanmitra Barman, Sriram Kanvah and Arnab Dutt

Plasmonic gold nanoprism-Cobalt molecular complex dyad mimics Photosystem-II for visible-NIR illuminated neutral water oxidation

Constructing an artificial assembly for efficient photocatalytic water splitting is key in the pursuit for a solar-driven renewable energy economy. Here, we have fabricated a covalently linked gold nanoprism�cobalt molecular catalyst construct that stimulated efficient photoelectrocatalytic water oxidation reaction. This assembly generated significant photocurrent (?50 ?A/cm2) in neutral aqueous conditions with a minimal onset overpotential (?250 mV). This dyad imitates the light-harvesting properties of natural photosystem-II by producing 0.66 ?moles of O2 and 1.32 ?moles of H2 simultaneously per hour (0.8% photon to chemical fuel conversion efficiency) following complete water splitting under light with ?0.075�0.01% incident photon to photocurrent conversion efficiency (IPCE). The presence of the plasmonic gold nanomaterial in this assembly instigates broad-band absorbance spanning from the visible to NIR region (400�1200 nm) covering the majority of the natural solar spectrum. This dyad construct also exhibited appreciable durability under photoelectrocatalytic conditions to demonstrate its prospective applications in alternative energy fields.by Ab Qayoom Mir, Gayatri Joshi, Piue Ghosh, Shikha Khandelwal, Ashish Kar, Ravi Hegde, Saumyakanti Khatua and Arnab Dutt

Plasmonic CoO-Decorated Au Nanorods for Photoelectrocatalytic Water Oxidation

Harvesting the full bandwidth of the solar spectrum, especially the near infrared portion, remains a challenge for solar-to-fuel conversion technology. Plasmonic nanostructures have recently attracted attention in this connection due to their enhanced yet tunable broadband absorption and photochemical stability. Here we report a nanoplasmonic photocatalytic construct by decorating plasmonic Au Nanorods with CoO for harvesting visible and NIR light via photo-electrochemical water oxidation reaction (WOR). In contrast to previous reports of plasmonic photocatalyst constructs, our structure does not require complicated fabrication or rely on rare-earth heavy-atom elements and exhibits excellent photostability without leaching of either cobalt or gold into the reaction solution under photoelectrochemical conditions. This catalytic construct triggered photo-electrochemical WOR with generation of significant photocurrent (~ 100 �Acm-2) while producing photogenerated oxygen at 18.1 mmoles h-1 of and hydrogen at 40.2 mmoles h-1 (on counter electrode) per miligram of cobalt under broadband excitation of 410-1700 nm with photon to oxygen conversion efficiency of ~0.05% in neutral aqueous conditions. The broadband photocatalytic activity of CoO-decorated Au Nanorod was attributed to the hot holes generated by the photoexcitation of plasmonic gold nanorods.by Piue Ghosh, Ashish Kar, Shikha Khandelwal, Divya Vyas, Ab Qayoom Mir, Arup Lal Chakraborty, Ravi S Hegde, Sudhanshu Sharma, Arnab Dutta and Saumyakanti Khatu

Key Experimental Considerations When Evaluating Functional Ionic Liquids for Combined Capture and Electrochemical Conversion of CO₂

Ionic liquids (ILs) are considered functional electrolytes for the electrocatalytic reduction of CO2 (ECO2R) due to their role in the double-layer structure formation and increased CO2 availability at the electrode surface, which reduces the voltage requirement. However, not all ILs are the same, considering the purity and degree of the functionality of the IL. Further, there are critical experimental factors that impact the evaluation of ILs for ECO2R including the reference electrode, working electrode construction, cosolvent selection, cell geometry, and whether the electrochemical cell is a single compartment or a divided cell. Here, we describe improved synthesis methods of imidazolium cyanopyrrolide IL for electrochemical studies in consideration of precursor composition and reaction time. We explored how IL with cosolvents (i.e. acetonitrile, dimethylformamide, dimethyl sulfoxide, propylene carbonate, and n-methyl-2-pyrrolidone) affects conductivity, CO2 mass transport, and ECO2R activation overpotential together with the effects of electrode materials (Sn, Ag, Au, and glassy carbon). Acetonitrile was found to be the best solvent for lowering the onset potential and increasing the catalytic current density for the production of CO owing to the enhanced ion mobility in combination with the silver electrode. Further, the ECO2R activity of molecular catalysts Ni(cyclam)Cl2 and iron tetraphenylsulfonato porphyrin (FeTPPS) on the carbon cloth electrode maintained high Faradaic efficiencies for CO in the presence of the IL. This study presents best practices for examining nontraditional multifunctional electrolytes amenable to integrated CO2 capture and conversion technologies for homogeneous and heterogeneous ECO2R