Based on this article
I have a SERP that does infinite scrolling to load results greater than 10.
How do I go about implement
rel=prev for that?
The first page in the sequence should not have any rel next or rel prev, the second page should have:
<link rel="next" href="http://www.example.com/article?story=abc&page=2"/>
<link rel="prev" href="http://www.example.com/article?story=abc&page=1"/>
And so on through the sequence until it finishes.
Since your page infinitely scrolls and these tags are designed to go into the
<head> of the page I don't think it's possible to implement these tags in your case - as there is actually only a single page.
rel=next links accordingly.
The only slightly tricky bit may be integrating your conventional and endless pagination methods seamlessly, so that, for example, a user who follows a link to a page in your conventional navigation scheme and has JS enabled will be shown the appropriate page in the endless scrolling navigation. The actual tricky part is doing that smoothly and efficiently, so that e.g. following a link to page 100 in the results won't crash my browser.
You might also want to make your infinite scrolling list make use of "hash-bang" URLs, so that a) your users can save links to specific points in your infinite list, and b) search engines that encounter such links can find their way to the appropriate page in the conventional list. For more information, see e.g. "How To: Allow Google to Crawl your AJAX Content".