The electron affinity of halogens are F = 322, Cl = 349, Br = 324, I = 295 kJ mol^-1' The higher value for Cl as compared to that of F is due to:

Electron affinity value of Cl is higher than that of F as Cl belongs to third period (have larger size)
while F belongs to second period (have small size). In Cl, electron-electron repulsion forces are weaker than that of F and hence, the extra electron which is to be added experience less electronic repulsions.