The tunability of electronic structure in intermetallics opens the door to systematic studies in catalysis. Here, we experimentally investigate various descriptors for the electrocatalytic nitrate reduction reaction using 9 Heusler phases as catalysts (Co₂VSn, Co₂MnAl, Co₂MnGe, Co₂MnSn, Co₂FeGe, Co₂MnSb, Ni₂MnSn, Co₂FeSi, and Co₂FeAl). In contrast to previous studies with Co-based Heusler phases and oxide perovskites for OER, we find that generally, the total valence electron count, rather than e_g filling, provides a better prediction of the activity. However, with period 5 Y elements such as Sn and Sb at high valence electron counts, Y-site d-band centers must also be considered. Reaction mechanism analysis by DFT also clarifies the role of X/Y sites. Hence, a single descriptor alone is not sufficient to rationalize catalytic activity across the full spectrum of Heusler phase compositions. So far, valence electron control has relied on single metal or binary alloy compositions for nitrate reduction, but these Heusler phases help decouple the element identity and valence count, while also serving as a guide for more catalysts based on ternary intermetallics. This work thus establishes multi-descriptor guidance for a wide group of catalyst compositions previously relatively unexplored.