In situ incorporation of cobalt nanoclusters and nitrogen into the carbon matrix: a bifunctional catalyst for the oxygen depolarized cathode and chlorine evolution in HCl electrolysis

Abstract

This study aimed at designing a simple and facile strategy of incorporating highly desirable nanoclusters of non-precious cobalt metal along with nitrogen (Co-NSC) into the carbon matrix for HCl electrolysis. The in situ co-insertion of Co and N was found to impart bifunctionality facilitating both the oxygen reduction reaction (ORR) at the oxygen depolarized cathode (ODC) and chlorine evolution at the chlorine evolving anode (CEA) in HCl electrolysis. Improvement in the kinetics and energetics of these reactions is expected to benefit from the improved energy quotient and waste HCl utilization towards greener commodity chemicals. Optimization of the Co-NSC catalyst synthesis was carefully performed using a Co-based complex by varying the thermal treatment conditions which largely impacted the composition of Co : N in the catalyst and also guided the obtainable morphology. Once synthesized a thorough investigation of the Co-NSC variants was performed using a range of physicochemical and analytical investigations to determine the most active Co : N composition and morphology facilitating bifunctional electrocatalysis at the ODC and CEA. The electrochemical activities observed were compared against those of benchmark and industrially applicable catalysts both under mild (0.4 M HCl) and stringent corrosive conditions (5 M HCl). Not just activity but stability of this carefully designed catalyst was later confirmed by performing accelerated degradation tests over the duration of a month and post analysis of the recovered catalyst. The visualization of the local electrocatalytic activity of the proposed catalyst towards the ORR was evaluated using scanning electrochemical microscopy.