Use of first person in a PhD Thesis Is there a non written rule to which person to use in the PhD thesis, 5 years of using "We" in the papers have brought me to the innate necessity to do it every time I describe something.

Recently, though, one of my lab-mates told me that I should use I, since it is your work, if the thesis were co-written, then it would be a different story.

Is there any standard in your universities, or do you have any preferred practice.
I generally avoid "I" in scientific texts altogether, though some authors are in fact using it if they are the sole author. I can't remember seeing it in a thesis though. In texts with a sole author, I usually understand "we" as meaning the author and the reader, and I'd suggest that it's fine to use it in places where it can have that meaning. For example something like "When substituting a by b, we get ..."

A generally useful advice would be to read into some of the theses written in your group, department, and university (in decreasing relevance), and see whether there is a common pattern.