TPyP-α was much less active and produced hydrogen at a rate of just 18 µmol g -1 h -1 , although the basic pyridyl groups in TPyP meant that a significant proportion of the TPyP-α catalyst (> 50 wt. % by filtration) dissolved in the acidic medium during this measurement. Consequently, a direct comparison between the HER activity of TPyP-α and TBAP-α in ascorbic acid is not possible. TPhP-α is stable in ascorbic acid but had an even lower HER of 2 µmol g -1 h -1 .