Why is a comma used to separate hydrogen gas and platinum when using cell notation? I have come across many online articles and books where I see the following:


  Gaseous electrode
  
  Gases such as $\ce{H2}$ and $\ce{Cl2}$ can act as anode and as cathode by loosing electrons ans by accepting electrons, respectively. For example,
  
  $\ce{Pt,H2 | H+}$ (acts as oxidation potential)
  or 
  \begin{align}
\ce{0.5 H2 (g)(\pu{1 atm}) &amp;-&gt; H+ (aq) + e-} \\
E_\mathrm{cell} &amp;= E_\mathrm{cell}^\circ -\frac{0.059}{1}\log{[\ce{H+}]} \\
 &amp;= 0 + 0.059\mathrm{pH}
\end{align}


Aren't the two species in different phases? If so, aren't they supposed to be separated by a '|' and not by a comma?
Since $\ce{Pt}$ is not a reactant and only a catalyst, one only wants to write $\ce{H_2}$ on the reactant side. When it is specified, since it is not involved in the reaction, the | is not warranted since Pt doesn't show up in the reaction as the comment by TAR86 pointed out.

Generally, the electrode material is not entered into the shorhand notation since the material of the electrode doesn't change the thermodynamic potential. In this case, the choice of $\ce{Pt}$ is critical and that is why it is specified. The potential of the electrode would be affected by the details of the measurement device with any other electrode material that is a worse catalyst.