Why do materials with low work functions emit electrons more easily?

The electronic work function represents the minimum energy required to remove an electron from the surface of a material. This value serves as a measure of how tightly a material holds its electrons; a lower work function indicates that electrons are less tightly bound to the surface.12

In the context of thermionic emission, electrons must acquire enough energy—typically through thermal collisions—to overcome the attractive force holding them within the material's structure. Because the rate of electron emission decreases exponentially as the work function increases, materials with lower work functions require less thermal energy to liberate electrons. Consequently, these materials emit electrons more easily, as a greater proportion of their mobile electrons possess sufficient energy to escape the surface barrier at a given temperature. This property is critical for the efficiency of thermionic power converters, where selecting an emitter with a small work function is essential for effective energy conversion.234