The heterogeneous electrochemical oxygen evolution reaction (OER) is dominated by transition metal (TM) oxides, and iron-doped nickel oxyhydroxide (Ni1-xFexOOH) has shown promise to replace precious-metal-based catalysts. We illuminated recently the exact roles of Fe and Ni in this oxide using a divide-and-conquer modeling approach. Specifically, we describe shorter-range interactions with the more accurate screened-exchange hybrid density functional theory (“hybrid DFT”) using smaller models and longer-range interactions using pure DFT with larger models. We identified that the combined abilities of Fe to form an optimally metastable terminal oxo as Fe(IV)=O and Ni(III)’s relatively facile reduction into Ni(II), which together facilitate reductive elimination of O2, yield an energy-efficient water oxidation process. In light of these two critical complementary features of Fe and Ni, here we report investigations of alternative dopants as primary active sites to replace Fe, and secondary redox active sites to replace Ni. Primary dopants are selected via the “oxo wall theory” of metal-oxo complexes, which states that TMs to the left of the Co group are able to form stable oxo species. Secondary dopants are chosen based on the reducibility of their +3 cation to form +2, relative to Ni. We find that Ni(III) in the host oxide strongly influences dopant oxidation state, in that most dopants spontaneously oxidize to their respective high oxidation states, while lattice Ni(III) concomitantly reduce to Ni(II). The stability of these high oxidation state cations renders these primary dopants inactive towards reductive elimination of O2. Finally, we predict that secondary dopants to the right of the Ni group promote O2 elimination without significantly altering the overall potential requirement for OER. Our work highlights the utility of analyzing the redox behavior of TMs in their molecular analogs in identifying important chemical features for efficient heterogeneous catalysts.

Oxygen evolution at low-lattice-coordinated NiOOH sites: Doping strategies from divide-and-conquer DFT/hybrid-DFT

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.