Electrothermal Annealing of Catalytic Platinum Microwire Electrodes: Towards Membrane-Free pH 7 Glucose Micro-Fuel Cells

Surface activation and cleaning of platinum micro-wires of 25 micron diameter has been achieved by a short one-second electrothermal annealing treatment in air at 0.3 A (to orange glow). Voltammetric data suggest a decrease in the electrochemically active surface area with annealing time and a change in surface structure towards the Pt(100) crystalline face. The impact of electrothermal annealing on the electrocatalytic activity towards (i) oxygen reduction and (ii) glucose oxidation in pH 7 phosphate buffered aqueous solutions is investigated. In contrast to as-received platinum, annealed platinum produces an electrocatalytic response towards glucose oxidation with increasing glucose concentration. A short one-second anneal step is just as effective in enhancing catalysis as prolonged electrochemical cleaning in sulphuric acid. Finally, by combining a non-annealed and an annealed microwire electrode, a very simple membrane-free micro-fuel cell system is devised operating in phosphate buffer at pH 7 with linearly increasing power output reaching 2.2 nW cm⁻² for high glucose levels of 0.5 M.