Transition-metal oxides that exhibit “pseudocapacitance” are promising alternatives to high-surface-area carbons as charge-storing materials in next-generation electrochemical capacitors (ECs). Hydrous ruthenium oxides remain the state-of-the-art for pseudocapacitive materials due to their fortuitous combination of high electronic and ionic conductivity. Lower-cost alternatives are being vigorously pursued, yet the low electronic conductivity of most other metal oxides of interest (e.g., MnOx) necessitates that they be thoughtfully incorporated with a conductive carbon support. We have developed an electrode design in which pseudocapacitive oxides, such as MnOx and FeOx, are applied as nanoscale coatings onto ultraporous carbon nanofoam substrates that define the macroscale-to-nanoscale structure of the resulting electrode architecture [1,2]. In addition to their practical advantages for device fabrication, these nanofoam paper-based materials have also provided a designer platform with which to investigate the interplay of pore structure and electrochemical performance [3] and for in situ analysis of the mechanisms responsible for pseudocapacitance [4].In the background of these studies, we have accumulated evidence that the physicochemical nature of the carbon–metal oxide interface can have a significant impact on electrochemical performance. While continuing to develop and transition our 3D electrode architectures, we are refocusing our research efforts on investigating fundamental charge-transfer properties at nanoscale carbon–metal oxide interfaces. Shifting from the characterization complexities of the nanofoam-based architectures, we use planar pyrolytic-carbon substrates to mimic the surface properties of 3D carbon, but in forms that are more readily characterized by conventional surface spectroscopy and scanning-probe microcopy techniques. We apply nanoscale pseuodocapacitive oxides to these planar carbon films using redox-deposition protocols previously demonstrated at 3D carbons [5], and explore how the physical, chemical, and electronic structure of the resulting carbon–metal oxide interface impacts electrochemical properties. Lessons learned from these model interfaces are readily translated to improved performance in practical 3D electrode architectures. 1. Fischer, A.E.; Saunders, M.P.; Pettigrew, K.A.; Rolison, D.R.; Long, J.W. J. Electrochem. Soc. 2008, 155, A246. 2. Sassin, M.B.; Mansour, A.N.; Pettigrew, K.A.; Rolison, D.R.; Long, J.W. ACS Nano 2009, 4, 4505. 3. Sassin, M.B.; Hoag, C.P.; Willis, B.T.; Kucko, N.W.; Rolison, D.R.; Long, J.W. Nanoscale, 2013, 5, 1649. 4. Beasley, C.A.; Sassin, M.B.; Long, J.W. J. Electrochem. Soc. 2015, 162, A5060. 5. Sassin, M.B. Chervin, C.N.; Rolison, D.R.; Long, J.W. Acc. Chem. Res. 2013, 46, 1062.