Platinum-Based Carbon Nanodots Nanocatalysts for Direct Alcohol Fuel Cells

*Sandile Surprise Gwebu, Philiswa N. Nomngongo and Nobanathi W. Maxakato*

#### **Abstract**

Platinum and its alloys are regarded as best nanocatalysts for the electro-oxidation of alcohol fuels especially in acidic conditions. The performance of nanocatalysts for alcohol fuel cells depends greatly on the support material. A good support material should have high surface area to obtain high metal dispersion. It should also bond and interact with the nanocatalysts to improve the activity of the overall electrode. Most importantly, the support material should offer great resistance to corrosion under the harsh fuel cell conditions. In this chapter, the use of carbon nanodots as support materials for Pt-Sn and Pt-TiO2 nanoparticles is discussed. The electrochemical activity of Pt/CNDs, Pt-Sn/CNDs and Pt/CNDs-TiO2 nanocatalysts was studied using cyclic voltammetry (CV) in acidic and alkaline conditions. Chronoamperometry (CA) was used to investigate the long-term stability of the nanocatalysts under the fuel cell environment. Electrochemical results demonstrated that binary Pt nanocatalysts are more active compared to monocatalysts. It was also observed that carbon nanodots are better support materials than carbon black. Blending carbon nanodots with titanium dioxide (a ceramic material) improves the corrosion resistance of the nanocatalyst. Cyclic voltammetry results also proved that alcohol electro-oxidation is enhanced in alkaline conditions.

**Keywords:** nanocatalyst, platinum, carbon nanodots, alcohol fuel cell, electrooxidation

#### **1. Introduction**

A fuel cell is an electrochemical device that transforms the chemical energy from a fuel into electrical energy through an electrochemical reaction without combusting the fuel [1, 2]. Fuel cell technology is one of the innovative future energy technologies all over the world. Fuel cells are environmentally friendly and more efficient than combustion engines. They operate at low temperatures quietly without vibration or noise; hence, can be used for both stationary and mobile applications. There are numerous types of fuel cells, classified according to the type of the electrolyte they use which governs the operating temperature and the catalyst suitable for those conditions.

Among the numerous types of fuel cells, direct alcohol fuel cells (DAFCs) are the most attractive using liquid and renewable alcohols (ethanol and methanol) as a fuel [3]. DAFCs are a very promising type when fuel consumption and feed strategies are taken into consideration. Unlike hydrogen fuel cells, which have safety, storage, and distribution challenges, DAFCs employ a liquid fuel that can easily be kept and transported [4, 5]. The electro-oxidation of alcohol fuels occurs on the surface of the positive electrode (anode) whereas the reduction of oxygen takes place on the negative electrode (cathode). DAFCs electrodes are made of conductive support material with a high surface onto which platinum nanoparticles are deposited. Platinum is the best electrocatalyst for alcohol oxidation reactions (AORs) in acidic conditions, nonetheless, it is expensive and it can effortlessly be poisoned by the intermediates that are formed during the AORs [6]. For these reasons, novel catalyst materials and catalyst preparation methods are still key topics studied in alcohol fuel cells. The efficiency of the electrocatalyst nanoparticles depends on the support material and its morphology [7]. Carbon nanomaterials have been considered for use as support materials because of their large surface area, great electrical conductivity, tensile strength, good thermal stability, corrosion resistance, ease of recovery and recyclability [8, 9]. In this chapter, the electrochemical performance of Pt/CNDs, Pt-Sn/CNDs and Pt/CNDs-TiO2 nanocatalysts is discussed. All the metal nanoparticles used in the studies reviewed were deposited on to the support materials by the alcohol reduction method.
