Catalytic Activity of Au-Cu Alloy on TiO2 Nanotubes for Alcohol Oxidation

Abstract

First fuel cell was discovered 180 years ago and still the ideal, namely cheap and effective catalytic materials are highly required. Such device allows to convert chemical energy into electrical one without pollutant gasses emission. In the case of alcohol fuel cells, methanol, ethanol, ethylene glycol and glycerine are considered as a power source. Platinum is commonly used for alcohol electrocatalyst, because of its high activity and stability. However, due to the high cost and limited supply platinum should be replaced by material that small amount is enough to reach satisfactory catalytic effect. In our work, we present the activity of gold-copper modified titania nanotubes toward electrocatalytic alcohol oxidation [1].The material is fabricated using three steps such as: 1) anodization of Ti plate, 2) thin 10 nm AuCu alloy layer magnetron sputtering, and 3) rapid thermal annealing in an argon atmosphere [2]. Scanning electron microscopy confirmed the presence of well-ordered TiO2 nanotubes (TiNT) with diameter of 101 ± 13 nm and length of 709± 53 nm. After AuCu alloy magnetron sputtering and thermal treatment spherical nanoparticles were formed on NT surface. Based on top view SEM images the diameter of gold copper nanoparticles is equal to 38 ± 5 nm. However, the TEM images showed that diameter of nanoparticles changes from 5 nm to 60 nm (Figure 1a-d) where the bigger particles are on the top of the nanotubes. Applied fabrication procedure allowed us to obtain electrode material that can be used in methanol, ethylene glycol or glycerine oxidation. The highest catalytic activity of AuCu alloy was obtained for glycerine oxidation. Prepared material exhibited 90 times higher current density after glycerine addition to the alkaline solution than pure TiNT (Figure 1e). Furthermore, higher current density towards alcohol oxidation was registered for thermally annealed sample (an-AuCu/TiNT) than for non-annealed one (n-AuCu/TiNT).Cyclic voltammetry measurements for the an-AuCu/TiNT in glycerine solution at different scan rates confirmed diffusion controlled process. The oxidation peak current density located at +0.3 V and +1 V grows up to 120 mV/s with slope of 51 and 81 µA/cm2 respectively, which confirmed more privilege process at +1 V vs. Ag/AgCl/0.1M KCl. We believe that the information reported in our work provide wider knowledge about new and more efficient electrodes for alcohol oxidation.Research is financed by National Science Centre (Poland): Grant No. 2019/35/N/ST5/02604[1] W. Lipińska et al. Journal of Materials Science, 57 (2022) 13345, DOI:10.1007/s10853-022-07471-7[2] W. Lipińska et al. ACS Applied Materials & Interfaces, 13 (2021) 52967, DOI:10.1021/acsami.1c16271 Figure 1