According to the I Need Air Songfacts,the song features Brooklyn-native singer/songwriter/producer Angela Hunte singing the hook. Hunte is best known for co-writing the original version of Jay-Z's hit, Empire State of Mind.
This song seems to seriously divide people. Personally I love it, I was quite surprised actually when I was the diversity of the comments. Possibly because I encountered it by watching a live video of it on the tube or something, dunno. (It must be wicked live, I can only imagine)
Oh btw, goran_p, you're absolutely right, the live version with Emeli Sande is breathtaking!