Nanostructured, Alkaline Titanate‐Converted, and Heat‐Treated Ti6Al4V Microspheres via Wet‐Chemical Alkaline Modification and their ORR Electrocatalytic Response

Abstract

This study describes the chemical conversion and heat treatment of Ti6Al4V microspheres (Ti6_MS), and the resulting effects on their electrocatalytic properties. The wet‐chemical conversion (5.0 m NaOH, 60 °C, 24 h; Sample label: Ti6_TC) converts the top surface of the Ti6_MS powder into an ≈820 nm thick sodium titanate surface. Heat‐treatment (Ti6_TC_HT) at 450 °C increases the stability of the surface, through partial titanate crystallization, while mitigating excess rutile formation. All samples are analyzed chemically (XPS, EDX, Raman, EELS), structurally (XRD and TEM), and morphologically (SEM, TEM), demonstrating the characteristic formation of sodium titanate dendritic structures, with minimal chemical, structural, and morphological differences due to the 450 °C heat‐treatment. The effect of the preparation methodology on oxygen reduction reaction (ORR) electrocatalytic performance is also tested. The introduction of the sodium titanate layer changes the mechanism of the ORR, from a mixed 4 electron/2 electron pathway to a predominantly 2‐electron pathway. By maintaining the microspherical nature of the material while also tuning the surface of the material toward different reaction mechanisms, a design strategy for new electrocatalyst materials is explored.