Table S1.

Volumetric current densities and specific activities of several representative Type I and II catalysts

SourceFig. no.Sample identifierCatalyst type (I or II)NPMC loading, mg/cm2O2/H2 absolute pressure, barReported original mass (A/g) or areal (mA/cm2) or volumetric (A/cm3) current density at 0.8 VReported extrapolated mass (A/g) or areal (mA/cm2) or volumetric (A/cm3) current density at 0.8 VNormalized volumetric current density (measured at 0.8ViR-free, H2/O2 is 1 bar), A/cm3Normalized volumetric activity (extrapolated at 0.8ViR-free, H2/O2 is 1bar), A/cm3
88Impregnation NCR2I11.5/1.516253.55.5
102A 100% NH3I11.5/1.522305.27.1
118BP_CV1I12.56/2.5639884.610.5
156(D)I11.5/1.5330.70.7
166(d)I3.81.5/1.524§241.51.5
192Large open circlesI11/118991899
810Ball milling NCR2II11.5/1.5661871644
176II1.62/212184.9††7.4
203StarsII11/13723037230
213II41/12013020130
22S6Zn(eIm)2TPIII2.21/15214652146
27S510/90II11.5/1.51322623162
This work1II21/16045060450
  • All of the volumetric current densities and activities are derived from peer-reviewed literature. The values are normalized to 1-bar reference pressure if not measured at 1 bar. The fuel cells were operated at 80 °C and 100% RH. The equation to convert mass activity, Im measured under pressures PO2 and PH2 into volumetric activity, I*v, under 1 bar of O2 and H2 pressures is as follows (ref. 19, equation S1):Iv=Imρeff(PO2PO2)0.79(PH2PH2)αC/2,

  • where P*O2 and P*H2 are the reference pressures (1 bar). ρeff is the effective density of carbon-based, porous NPMC electrode, which is set at 0.4 g/cm3 (19). αc is the cathodic transfer coefficient and is assumed to be 1.

  • Reported mass activity.

  • Normalized volumetric current density is converted from the reported mass activity based on the equation above.

  • § Reported areal activity.

  • Normalized volumetric current density is converted from the reported areal activity based on the equation above.

  • Reported volumetric activity.

  • †† Normalized volumetric current density is converted from the reported data based on the equation above.