Is it permissible to create a section in forums dedicated to collecting supplications from members to build an encyclopedia of supplications?

There is no objection to creating an encyclopedia of supplications (du'as). It is preferable that the added supplications be authentic and reported from the Prophet, peace and blessings be upon him, with an explanation of the Hadith (definition)'s source and درجه (degree of authenticity) for increased benefit. It is permissible to add supplications that are not reported (from the Prophet), although it is better to limit it to those that are reported.