You haven't shown us the class of HexVal. From the error you get with Paolo's answer I suspect that HexVal is an Nx4 char array.
You could split it into a Nx2 cell array of 1x2 char vectors. It's trivial to do and also pointless and more likely will make the rest of the code more complicated. It's much simpler to use indexing to get whichever characters you want. It's simple column indexing. e.g. to get the first two characters of each row:
for the other 2.
If you do really want to physically split the columns (again, it's pointless):
mat2cell(HexVal, ones(size(HexVal, 1), 1), [2 2])