Patrick,
I believe that when you make calls to the functions inside of concs, you need to include the arguments for those functions. Should look something like:
concs=@(t,y)[y(3).*Et(t);
y(4).*Et(t);
-k1.*y(3).*y(4);
-0.5.*k1.*y(3).*y(4)-1.5.*k2.*y(4).*cCt(y)];
