Abstract
Recent investigations reported in the open literature concerning the functionalization of graphene as a support material for transition metal nanoparticle catalysts have examined isolated systems for their potential Oxygen Reduction Reaction (ORR) activity. In this work we present results which characterize the ability to use functionalized graphene (via dopants B, N) to upshift and downshift the adsorption energy of mono-atomic oxygen, O* (the ORR activity descriptor on ORR Volcano Plots), for various compositions of 4-atom, 7-atom, and 19-atom sub-nanometer binary alloy/intermetallic transition metal nanoparticle catalysts on graphene (TMNP-MDG). Our results show several important and interesting features: (1) that the combination of geometric and electronic effects makes development of simple linear mixing rules for size/composition difficult; (2) that the transition from 4- to 7- to 19-atom TMNP on MDG has pronounced effects on ORR activity for all compositions; (3) that the use of B and N as dopants to modulate the graphene-TMNP electronic structure interaction can cause shifts in the oxygen adsorption energy of 0.5 eV or more; (4) that it might be possible to make specific doped-graphene-NixCuy TMNP systems which fall close to the Volcano Peak for ORR. Our results point to systems which should be investigated experimentally and may improve the viability of future fuel cell or other ORR applications, and provide new paths for future investigations of more detail for TMNP-MDG screening.
Highlights
In this new work presented in this manuscript, we show the ability of dopants in the graphene support to significantly modulate the adsorption energy of mono-atomic oxygen on 4-atom, 7-atom, and 19atom transition metal nanoparticles (TMNP) of various binary alloy/intermetallic compositions
The values of the ground state total energies for the 7 and 19atom TMNP-MDG are reported in Figure 3, with the energies of the graphene sheet and corresponding stoichiometric amount of TMNP included as the reference state
A volcano plot for the electrochemical Oxygen Reduction Reaction (ORR) was developed through thermodynamic scaling relations calculated density functional theory (DFT) (Lozano and Rankin, 2018; Rankin and Lozano, 2019)
Summary
The use of advanced, -engineered paired catalyst-support systems is likely the key to advancing the field in pursuit of several transformational technologies related to reduction of small molecules such as O2, CO2, and N2 (Nørskov et al, 2004; Gasteiger et al, 2005; Ferguson et al, 2012; Wang C. et al, 2012; Zhu and Dong, 2013; Staszak-Jirkovský et al, 2016; Chaves et al, 2017; Zhu et al, 2017; Halder et al, 2018; Hussein and Johnston, 2018; Lozano and Rankin, 2018; Rankin and Lozano, 2019). Oxygen (and Hydroxyl) are key intermediates in the ORR and the adsorption of mono-atomic oxygen, O*, on the catalyst surface is typically given as the descriptor necessary to predict the performance of a TMNP for the ORR (Nørskov et al, 2004; Gasteiger et al, 2005; Wang C. et al, 2012; Lozano and Rankin, 2018; Rankin and Lozano, 2019)
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