Andrew Wong1 Joseph Gauthier1 Frauke Kracke2 Antaeres Antoniuk-Pablant1 Christopher Hahn1 3 Karen Chan1 3 Alfred Spormann2 4 Thomas Jaramillo4 1 3

1, SUNCAT Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, Stanford, California, United States
2, Civil and Environmental Engineering, Stanford University, Stanford, California, United States
3, SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, Menlo Park, California, United States
4, Chemical Engineering, Stanford University, Stanford, California, United States

Improving the performance of cathodes for the electrochemical CO2 reduction reaction (CO2RR) will benefit from the discovery of new materials as well as the introduction of new paradigms. This presentation focuses on the synthesis and systematic study of the CO2 reduction activity of a novel quasi-2D PdPt bimetallic ‘nanoclam’ catalyst synthesized on carbon cloth electrodes via a pulsed electrodeposition technique. These results highlight the importance of nanostructuring to improve selectivity and geometric activity for CO2 reduction in this system through the comparison of the bulk and nanostructured PdPt. In addition, we also propose that the high activity of this catalyst at low overpotential is ideal for paring with biological systems to realize a hybrid system for CO2 reduction.

The PdPt nanoclams have a unique tapered morphology that combines high surface area with exposure of numerous undercoordinated sites for CO2 reduction with activity exceeding that of either Pd or Pt for CO2 reduction to formate at 0.2 V vs RHE, which is a provocative result. In comparison with bulk Pd, PdPt, and Pt systems, we find that the interplay of multiple trends affects selectivity and activity:
1. Increasing Pt content shifts selectivity from formation of formate to hydrogen evolution in the bulk
2. Increasing Pt content increases overall activity and prevents catalyst deactivation by changing the energetics of hydride intercalation into PdPt
3. Nanostructured morphology of PdPt nanoclams increases selectivity to formate in PdPt nanoclams vs in bulk, planar PdPt.

In addition to this understanding, we report our initial results on the creation of a hybrid electrochemical-biological CO2 reduction system in which formate and hydrogen are produced through electrochemical CO2 reduction by PdPt nanoclams. These products are metabolized by methanogens in combination with CO2 to yield ~100% faradaic efficiency to methane. Going forward, the integration of microbial communities with these nanostructured PdPt catalysts has the potential to combine the best-of-both-worlds from electrochemical and biological systems to achieve a regenerative catalytic system with high-selectivity, high activity, and low overpotential.