[en] For a wide range of high-precision experiments in physics, well-defined electric potentials for achieving high measurement accuracies are required. An accurate determination of the electric potential is crucial for the measurement of the neutrino mass (KATRIN) as well as the measurement of the e"- anti ν_e correlation coefficient a in free neutron decay (aSPECT). Work function fluctuations on the electrodes lead to uncertainties in the distribution of the electric potential. For aSPECT, the electric potential has to be known at an accuracy of 10 mV. However, due to the patch effect of gold, work function fluctuations of several 100 meV can occur. Therefore, the work function distributions of the gold-plated electrodes have been measured using a Kelvin probe. Furthermore, the change of work function distributions over time as well as the influence of relative humidity on the work function measurement have been investigated. For aSPECT, the work function distributions of the gold-plated electrodes have been measured using a Kelvin probe. Due to the patch effect of gold, work function fluctuations of up to 160 meV occur. This would lead to a significant uncertainty of the potential barrier, which should be known at an accuracy of 10 mV. Furthermore, the change of work function distributions over time as well as the influence of relative humidity on the work function measurement have been investigated.