What parameters do you consider for this selection, generally?

There is probably only one important parameter when hiring: don't make me struggle to discover why you're the best fit for my group. For example, you mention three broad fields of study; chemical, mechanical and energy. Which area are you most qualified? What proof do you have to demonstrate your experience and expertise?

As a professor, you probably know this, professors have a lot to do in a day. Researching on your qualifications and cracking their heads on a project they can fit you is not one of them.

I think a better way to use ResearchGate for possible hiring is to prepare a full proposal for a research project. Send it to the people who are already working in that area together with your CV.

Good luck.