In this work, we focused on the evaluation of oxygen evolution reaction (OER) activity of three different shapes of α-MnO₂ nanowires (NWs), nanorods (NRs) and nanotubes (NTs) in alkaline anion exchange water electrolyser. We have attempted to separate the effect of shape, surface area, Mn³⁺ content and crystal facets on OER activity and stability. X-ray Photoelectron Spectroscopy (XPS) measurements showed that NTs had the highest surface concentration of Mn³⁺ on the as prepared samples with average Mn oxidation state of 3.33. However, after activation an increase in the average oxidation state of all three shapes to 3.9 was confirmed by XPS. X-Ray Diffraction (XRD) showed surface restructuring after testing. MnO₂ NWs showed the highest OER mass activity of 60.6 A g⁻¹ (10 mA cm⁻² at 1.67 V (RHE)) due to the higher surface area of 72.2 m² g⁻¹. While NTs showed the highest specific activity due to highest content of 211 facet, high Mn³⁺ surface concentration/surface defects. Similar trend was observed in electrolyser testing with 2 mg cm⁻² loading. Poor electronic conductivity of MnO₂ resulted in decrease in performance with increased loading to 4 mg cm⁻². All the studied shapes showed good stability over 36 h of electrolyser testing.