Template free-synthesis of cobalt–iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

Abstract

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt–iron chalcogenides [Co_0.8Fe_0.2S₂ and Co_0.8Fe_0.2Se₂] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(VI)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec⁻¹) for Co_0.8Fe_0.2Se₂ and Co_0.8Fe_0.2S₂ respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(VI) reduction to Cr(III). Besides the maximum current achieved for Co_0.8Fe_0.2S₂, a minimum value for the Limit of detection (LOD) was obtained for Co_0.8Fe_0.2S₂ (0.159 μg L⁻¹) compared to Co_0.8Fe_0.2Se₂ (0.196 μg L⁻¹). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.