Zirconium foils (99.5% purity, 0.127 mm thickness) were ultrasonicated in acetone, ethanol, and deionized water for 10 mins each and dried in N 2 prior to electrochemical anodization. The anodization comprised of a single-step process using a high-voltage potentiostat (Jaissle IMP 88 -200 PC) in an electrochemical cell consisting of a circular working area of 1 cm 2 and a platinum counter electrode in a typical two-electrode setup. The organic electrolyte used is based on the previous work of Raghu et al. contains 2 wt% NH 4 F (Sigma Aldrich), 2 wt% H 2 0, 30 % Formamide (Carl Roth) in Glycerol (Carl Roth) The homogenously thick ZrNT was fabricated by ramping the potential from 0 to 90V over 60 seconds, followed by holding at 90V for 2 hours. The two types of modulated ZrNT structure (M 1 and M 2 ) were anodized in two voltage regimes (20 v -90 v). The modulated structure type 1 (M 1 ) involves ramping the voltage to 20 V for 60 seconds and holding at 20 V for 1 hour to obtain the first nanotubular layer. Thereafter, ramping down to 0 V for 60 seconds, subsequently, the voltage is ramped up again to 90 V for 60 seconds and held for 2 hours to achieve the second layer. The type 2 modulated structures (M 2 ) entails the same voltage condition as M 1 to obtain the second layer but the first layer was obtained by anodizing at 20 V for 4 hours, after ramping up gradually for 60 seconds. The current density and voltage during anodization were recorded and monitored by the ECM-Win software. Post-anodization involved rinsing with deionized water and soaking in ethanol for 10 mins to dissolve remains from the organic electrolyte, followed by annealing at 350 ͦ C for 1 hour, aimed towards the elimination of fluorides present in the as-formed nanotubes, whilst improving phase crystallinity of the NTs