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Strategies to improve electrocatalytic hydrogen evolution in tantalum nitrides through nanostructuring into 1D fibres and self-supported architectures.

Strategies to improve electrocatalytic hydrogen evolution in tantalum nitrides through nanostructuring into 1D fibres and self-supported architectures.

Date24th Mar 2023

Time03:00 PM

Venue Online meeting

PAST EVENT

Details

Tantalum-based carbides and nitrides have shown promise as electrocatalysts for the hydrogen evolution reaction (HER) due to their near-zero Gibbs adsorption free energy and theoretical current densities on par with MoS2. However, the practical realization is never achieved due to a strong affinity towards oxygen resulting in the formation of TaON layer, the electrocatalytic activity of which in pristine form is not fully understood. Also, no studies exist on development of 1D fibres which bestow superior electron and mass transport properties, thereby improving the electrocatalytic activity. To address these, mitigation strategies involving the use of centrifugal spinning and self-supported architectures were employed which offers significant advantages in the design of efficient and scalable electrocatalysts for the hydrogen evolution reaction. Centrifugal spinning offers a promising alternative approach to generate 1D fibers with high production rates, overcoming the drawbacks of conventional electrospinning. For the first time 1D TaON fibres, developed using in-house built centrifugal spinning setup demonstrated low Hydrogen evolution over potentials (250 mV) to achieve stable current densities (10 mA/cm2) in 0.5 M H2SO4. In comparison Ta2O5 oxide fibres by virtue of their poor electronic conductivity could deliver only 1 mA/cm2 at the same over potential. Further, the enhanced activity of oxynitride fibres was observed to be suppressed in the basic medium wherein high charge transfer resistance (261.7 Ω), low double layer capacitance (0.61 mF) was observed. This depreciation in performance was attributed to high oxyphilicity of tantalum ions in basic medium leading to poisoning of the active sites. Additionally, self-supported electrocatalysts eliminate the use of expensive binders and offer better prospects for stable performance over longer working conditions. These techniques, combined with the use of tantalum foil and earth abundant oxygen free nitrogen precursors such as NH4Cl, thiourea, melamine was subjected to vacuum annealing to grow TaN/Ta and its electrocatalytic hydrogen evolution kinetics was studied. At a fixed over potential of 350 mV vs RHE, Ta / thiourea delivered 8 mA/cm2, whereas only 0.8 mA/cm2 was obtained with Ta/melamine. Electrochemical impedance spectroscopy also exemplified that Ta / thiourea offers low resistance (2.5 Ω) when compared with Ta / melamine (40 Ω). The presence of graphitic Ta-C-S layer on Ta foil obtained during the decomposition of thiourea was attributed to enhance the hydrogen evolution kinetics.

Speakers

Mr. Raghunath Sharma (MM16D400)

Department of Metallurgical and Materials Engineering