Abstract
Asymmetric reactors having the configuration (Pt vertical bar Nafion vertical bar M-Cu, M = Pt, Pd) were designed and applied to the electrocatalytic nitrate reduction reaction (NRR) with no supporting electrolyte. The electrochemically-fabricated Cu-M (M = Pt, Pd) catalysts showed a highly-efficient catalytic activity by effectively reducing more than ca. 99% of nitrate ions, under static-reactor conditions, with first-order rate constants of ca. 0.040 min(-1) and ca. 0.057 min(-1) for Cu-Pt and Cu-Pd, respectively. Similar reactivity trends were observed under flow mode irrespective of flow rates while NRR rates were predominantly controlled by diffusion-limited mass-transfer. A maximum of ca. 93% nitrate removal at Cu-Pd catalyst was achieved within ca. 60 min. The comparatively lower CuO content of ca. 9%, as confirmed by XANES, resulted in a greater number of free NRR active sites inducing the superior catalytic activity of the Cu-Pd catalyst. On the other hand, NRR product selectivity investigations showed that Cu-Pd catalyst was highly ammonia-selective with a maximum of ca. 24% selectivity at a flow rate of 0.1 mL min(-1), while Cu-Pt catalyst was much selective to intermediate nitrite ions reaching a maximum of ca. 35% selectivity at the same flow rate. (C) 2015 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.