I could find no extensive biographical information on Moll on the first few pages of a Google search. But you can glimpse his career by linking here, here and here.
As this Wikipedia entry indicates, the Vienna Secession was essentially a rejection of, or rebellion against, the academic traditions and organizations of the city. But it did not promulgate any particular replacement style: Secession artists were basically free to do what they wished.
In Moll's case, this was to paint slightly simplified landscapes and townscapes, though his earlier paintings (and a fair number of Secession-era works) were traditional in style. He also seems to have followed his almost exact contemporary and fellow-Secessionist Gustav Klimt's landscape preference for square canvasses. Not having seen it in person, I'm not sure if I can call Moll's art great, but most of what I've found on the Web seems competently done and pleasing.