Application of Femtosecond Laser Surface Processed Electrodes in Electrolysis of Water

Femtosecond laser surface processing (FLSP) is a machining technique used to develop functionalized surfaces consisting of micro and nano-scale features. Metal electrodes processed using this technique can be used in water electrolysis to facilitate more efficient hydrogen and oxygen gas production. This thesis explores the electrochemical behavior of femtosecond laser processed 316SS electrodes in water electrolysis. The multi-scale surface structure size and separation were controlled through laser fluence and incident laser pulse count. The electrodes were studied in a three electrode electrolysis cell containing a 3M KOH(aq) electrolyte, FLSP 316SS working electrode, 316SS counter electrode, and Hg/HgO reference electrode. Through linear scan voltammetry, it was found that the FLSP electrodes reduced the voltage required to stimulate 1 A of current through the electrochemical cell by 191 mV, compared to polished 316SS. FLSP of the electrodes enhanced electrochemical efficiency through multiple mechanisms including increased electrode surface area, increased wettability, and modified bubble production behavior. Surface area analysis was conducted using confocal microscopy and current density versus voltage plots. Plasma cleaning of a polished and FLSP electrode was utilized to study the effects of wettability. Results indicated that both surface area and wettability contributed to the voltage decrease. Tafel analysis of the voltammetry scans indicated that the surface processing did not affect the surface chemistry of the electrodes, in regards to electron transfer kinetics. The final contribution to the voltage reduction was attributed to reduction in gas bubble size produced at the FLSP electrodes. Visual inspection confirmed that a FLSP electrode reduced the bubble diameter and bubble growth time until release from the electrode surface. Further investigation into affected bubble production of a FLSP surface is necessary to identify the full effects of bubble size and release time reduction. The electrochemical enhancements resulting from the FLSP technique show that the efficiency of a common industrial electrode material can be increased through surface structuring without the addition of surface coatings or changes in geometric area. Advisor: Dennis R. Alexande