The modulated selectivity for CO2RR towards MeOH over CO is likely due to a change in the CO absorption step. To explore this, we applied Grand Canonical DFT to examine the energetics as a function of chemical potential. Our Grand Canonical Potential Kinetics (GCPK) method keeps the applied potential constant for the initial and product states of each reaction step, just as in experiment (see Methods for more details). For CoPc on the SWCNT, we use the curved CoPc generated from the MD simulation as the starting point. For CoPc on the MWCNT, we start with the typical CoPc catalyst with D4h symmetry. Liao and coworkers recently suggested that at -1.0 V vs. RHE (-1.4 V vs. SHE at pH=6.8), the CoPc catalyst is spontaneously reduced to CoPcH4 in water. Specifically, the 4 outward N of the Pc ligand are hydrogenated (hence PcH4) with a free energy change of -2.92 eV relative to CoPc at 298.15 K. Thus, for our calculations we hydrogenate the 4 outward N of the Pc ligand for both curved and flat CoPcH4. These hydrogenations are not likely to cause Co demetallization since the reductions do not occur at the Co-N sites. The CO absorption energy as a function of applied potential is shown in Fig. . We see that for the calculated potential window, the curved CoPc has stronger CO binding than the flat CoPc. At In Fig. , the curved CoPcH4 is higher in energy than the flat analog due to the induced strain. However, the curved CoPcH4(CO) is lower in energy than the flat analog, because the strain makes for favorable CO binding. These two factors lead towards improved CO binding for curved CoPc, which ultimately improves MeOH selectivity.