Tailoring of poly[Ni(OH)2salen] nanoparticle-based electrocatalysts for effective urea remediation†

Abstract

There is no universal recipe for the proper structure tuning of Ni(OH)₂ nanoparticle (NP)-based catalysts for efficient urea electrooxidation (UOR) in alkaline media. However, it is known that fast generation of Ni³⁺OOH-type catalytic centers that are sustained and resilient during the overall catalytic process is crucial. Towards this, we report how we optimized and compared operating conditions and structural tuning of poly[NP-Ni(OH)₂SaltMe] and poly[meso-NP-Ni(OH)₂SaldMe] electrocatalysts active in alkaline media towards UOR. We started with studies of morphological differences evoked by the use of different NaOH_aq concentrations for catalyst fabrication by SEM and TEM. Then, we distinguished the most promising molecular structures of fabricated catalysts featuring the highest poisoning resistance and in situ generation of poly(NP-Ni³⁺OOHsalen) electrocatalytic centers for UOR. Furthermore, we found the best conditions for operation of both structured UOR catalysts using a comprehensive electrochemical approach. This approach involved multiple scan rate, Tafel slope, and activation energy (E_ac) analysis to finally compare which structured poly[NP-Ni(OH)₂salen] catalyst produces catalytic current more efficiently in response to a change in applied potential. Ultimately, we performed a longevity/durability test under real-system mimicking conditions. The fabricated catalysts constituted good platforms for studying the surface-remaining and bulk-remaining types of catalytically active sites of poly[NP-Ni(OH)₂salen]s for UOR activity. Our findings point to the bulk-structure-reactivity requirements of poly[NP-Ni(OH)₂salen]s, emphasizing their catalytic durability and effectiveness.