Atomic Layer Deposition By Surface-Limited Redox Replacement Synthesis of Highly Active and Durable CuxAu(1–x)catalysts for Nitrate Electroreduction

Abstract

The nitrate pollution from fertilizer and animal waste has become a severe environmental problem in recent years. High concentration of NO3-ions in surface water could impair the health of human beings.1The global trend for environmental compatibility has led to increasing demand for removing nitrates using environmentally friendly approaches that meet energy conservation standards.2Due to the low cost and controllable selectivity, the electro-reduction of NO3-ions promoted by metallic or bimetallic catalysts has been considered the among the most promising means for denitrification.3 In order to enhance activity and durability, and minimize the use of expensive catalytic materials, deposition of ultrathin metal/alloy films with controllable thickness and composition has attracted broad attention in last decades. Electrochemical atomic layer deposition (E-ALD) approaches for the growth of single metal films such as Pt and Pd have been developed by our group based on surface-limited redox replacement (SLRR) in one cell configuration.4,5The application of SLRR for deposition of alloy films has been taken as challenge and thoroughly studied in this report. CuxAu(1–x)bimetallic ultrathin-film catalysts have been synthesized using E-ALD by SLRR of Pb underpotentially deposited layer.6 The composition of synthesized alloy ultra-thin film could be controlled by the ratio of [Cu2+] ions and [AuCl4 –] complex in the deposition solution along with the application of specifically designed routine facilitating the administration of SLRR cycles. The alloy film composition has been determined by X-ray photoelectron spectroscopy and indirectly estimated by anodic stripping voltammetry. The nitrate electroreduction activity and durability of CuxAu(1–x)thin films, Cu thin film, and bulk Cu have been studied by one- and multiple-cycle voltammetry. The synthesized CuxAu(1–x)thin films feature up to two times higher nitrate electroreduction activity in acidic solution compared to bulk and thin-film Cu counterparts. Highest activity has been measured with a Cu0.70Au0.30alloy catalyst. Durability tests have demonstrated that Cu thin films undergo rapid passivation losing 65% of its peak activity for up to 100 cycles, whereas Cu0.70Au0.30catalysts developed in this study lose about 40% of their top performance. The significantly better durability of alloy films can be attributed to effective resistance to poisoning and/or minimized passivation of Cu active centers. It has been also found that both CuxAu(1–x)and pure Cu thin films show best electroreduction activity at lowest pH. References Moorcroft, M. J.; Davis, J.; Compton, R. G. Detection and determination of nitrate and nitrite: a review. Talanta 2001, 54, 785− 803Martínez, J.; Ortiz, A.; Ortiz, I. State-of-the-art and perspectives of the catalytic and electrocatalytic reduction of aqueous nitrates. Appl. Catal., B 2017, 207, 42−59Duca, M.; Koper, M. T. M. Powering denitrification: the perspectives of electrocatalytic nitrate reduction. Energy Environ. Sci. 2012,5,9726−9742.Dimitrov, N. Recent Advances in the Growth of Metals, Alloys, and Multilayers by Surface Limited Redox Replacement (SLRR) Based Approaches. Electrochim. Acta 2016, 209, 599−622.Dimitrov, N.; Achari, I.; Ambrozik, S. Palladium Ultrathin Film Growth by Surface-Limited Redox Replacement of Cu and H UPD Monolayers: Approaches, Pros, Cons, and Comparison. Electrochem. Soc. Interface 2018, 27, 65−69.Xie, Y.; Dimitrov, N. Highly Active and Durable Cu x Au (1–x) Ultrathin-Film Catalysts for Nitrate Electroreduction Synthesized by Surface-Limited Redox Replacement. ACS Omega. 2018, 3 (12), 17676–17686.