Reducing Pt loading in hydrogen evolution reaction (HER) catalysts is critical to developing widespread electrochemical water splitting systems. Transition metal carbide (TMC) catalysts have been shown to allow for reduced Pt loading by serving as substrates. Computational studies of potential HER catalysts have focused mainly on identifying materials with hydrogen binding energies (HBEs) similar to that of pure Pt. However, HER activity is governed by many other factors in addition to the HBE. Using first-principles quantum mechanics calculations, we perform a thorough verification of our previous prediction that monolayer Pt on a Mo2C substrate could serve as an effective replacement for pure Pt as an HER catalyst. We first determine that the HBEs of Pt/Mo2C and Pt are almost identical. We next show that the electronic structure of Pt/Mo2C exhibits the qualities desired in an HER catalyst: a d-band that spans the Fermi level and a strong overlap between the catalyst dd-band and hydrogen 1s band. Crystal orbital overlap population analyses reveal that the bonding and antibonding characteristics of Pt/Mo2C are as balanced as they are in Pt. Finally, our calculation of the double-layer capacitance (DLC) shows that the Pt overlayer, in addition to improving the bonding characteristics between the substrate and hydrogen, reduces the DLC relative to pure Mo2C. This work demonstrates that it is unnecessary that the substrate BE valence isoelectronic to Pt to serve as an effective catalyst support, in contrast to previous explanations for the success of Pt/TMC hybrid systems. Thus, in addition to demonstrating that Pt/Mo2C is well-suited for acting as an HER catalyst, this work provides an example of a more rigorous methodology for screening materials for their suitability as HER catalysts.