Compartmentalization is a viable approach of ensuring the turnover of a solution cascade reaction with ephemeral intermediates, which may otherwise deactivate in the bulk solution. In biochemistry or enzyme-relevant cascade reactions, extensive models have been constructed to quantitatively analyze the efficacy of compartmentalization. Nonetheless, the application of compartmentalization and its quantitative analysis in non-biochemical reactions is seldomly performed, leaving much uncertainty about whether compartmentalization remains effective for non-biochemical, such as organometallic, cascade reactions. Here, we report our exemplary efficacy analysis of compartmentalization in our previously reported cascade reaction for ambient CH4-to-CH3OH conversion, mediated by O2-deactivating RhII metalloradical with O2 as the terminal oxidant in Si nanowire array electrode. We experimentally identified and quantified the productivity of key reaction intermediates, including RhII metalloradical and reactive oxygen species (ROS) from O2. We subsequently determined that the nanowire array enables about 81 % of the generated ephemeral intermediate in air, RhII metalloradical, to be utilized towards CH3OH formation, which is 0% in homogenous solution. Such an experimentally determined value was satisfactorily consistent with the results from our semi-quantitative kinetic model. The consistency suggests that the reported CH4-to-CH3OH conversion surprisingly possesses minimal unforeseen side reactions, and is favorably efficient as a compartmentalized cascade reaction. Our quantitative evaluation of the reaction efficacy offers design insights and caveats into application of nanomaterials to achieve a spatially controlled organometallic cascade reactions.