Residual hydrogen concentration levels in graphite

Hydrogen concentration versus depth profiles obtained with secondary ion mass spectrometry of a high‐purity graphite (POCO) indicate that unannealed POCO has a residual subsurface H level on the order of 0.4% H/C. Vacuum annealing to 910 °C for several hours reduces this level by over an order of magnitude. However, reabsorption of hydrogen containing gases during air exposure occurs in the near surface region. Prolonged air exposure brings the residual hydrogen level within 5 μm of the surface back to the levels seen in unannealed POCO samples.