We know when two metals are placed togather electron transfer from metal with lower work function to that with lower work function. What may be the possible reason for this?
in fact, the electron transfer occurs from the donor state to an acceptor state in the system to reach the stationary state cross potential at the interface. The potential at the interface depends on the work functions of two materials. You can see my literature
You asked "What is the reason for electron transfer from higher work function (HWF) metal to that of lower work function (LWF) metal".
The question should be "What is the reason for electron FLOW from (LWF) metal to that of (HWF)" because actually a metal with (HWF) has a more positive quality than a metal with (LWF) and thus electrons (being negativly charged) will naturally move towards a more positive location.