What to do with negative research outcomes (results) of PhD research experiment? It is an expectation that the PhD would make an original contribution and/or advance knowledge  in a given field. I understand this is a universal assumption for this level of study across all universities.

One of my friend's research experiment has not produced a single positive result. This was a science experiment, so it is easy to quantify whether the result is positive or negative.

[It is a bit different in the social sciences, where the outcome (result) would be that either the null hypothesis is supported or rejected (with some analysis on the effect size to make the analysis meaningful in a given context). In other words, the data analysis either supports or does not support the proposition that is being investigated.]

My question is: What should a student do if none of the research outcomes or results are positive? 

Simply writing that nothing new was found does not add or advance knowledge other than to just confirm the status quo (which I guess is a form of contribution, but there has to be more than this at this level of research!).
Your friend might not want to hear this, but there's nothing you can do except for start over - with a different experiment. Research fails - and should  ! If there isn't a risk of failure, you're not out on the cutting edge doing research. 

But in most failures, there's a grain of something to build on ("from the ashes of disaster come the roses of success"). Maybe the student is too demoralized right now to see it, but almost always there's some clue in the failure that leads to a different research question worth asking.