Discussion Forum

greetings,

i am currently working on a model of the hydrogen evolution reaction using the interfaces transport of diluted species, chemistry, and surface reactions. The reaction mechanism i am modeling goes something like this

H+ + e- + * => H*

2H* => H2 + 2*

where * denotes a surface site

i would like to model the reaction with the initial condition that there is 1 monolayer of hydrogen adsorbed on the catalyst surface, so I have applied that condition in Surface Reactions.

i am starting with 0 concentration of H2, and the rate of the second reaction is given by k[H*]^2, where k is a positive rate constant. i have applied a "surface reactions" condition in transport of diluted species to the boundary that I envision the catalyst is at.

however, I have noticed that despite this reaction being the only "source/sink" of H2, the concentration of H2 initially increases near the boundary, then decreases. weirdly, when I change the initial condition so that initial hydrogen coverage is 0, H2 is increasing continually as expected.

simplified version of the model attached below, any thoughts appreciated.