A General Strategy to Atomically Dispersed Precious Metal Catalysts for Unravelling Their Catalytic Trends for Oxygen Reduction Reaction

Abstract

Atomically dispersed precious metal catalysts have emerged as a frontier in catalysis. However, a robust, generic synthetic strategy toward atomically dispersed catalysts is still lacking, which has limited systematic studies revealing their general catalytic trends distinct from those of conventional nanoparticle (NP)-based catalysts. Herein, we report a general synthetic strategy toward atomically dispersed precious metal catalysts, which consists of "trapping" precious metal precursors on a heteroatom-doped carbonaceous layer coated on a carbon support and "immobilizing" them with a SiO 2 layer during thermal activation. Through the "trapping-and-immobilizing" method, five atomically dispersed precious metal catalysts (Os, Ru, Rh, Ir, and Pt) could be obtained and served as model catalysts for unravelling catalytic trends for the oxygen reduction reaction (ORR). Owing to their isolated geometry, the atomically dispersed precious metal catalysts generally showed higher selectivity for H 2 O 2 production than their NP counterparts for the ORR. Among the atomically dispersed catalysts, the H 2 O 2 selectivity was changed by the types of metals, with atomically dispersed Pt catalyst showing the highest selectivity. A combination of experimental results and density functional theory calculations revealed that the selectivity trend of atomically dispersed catalysts could be correlated to the binding energy difference between *OOH and *O species. In terms of 2 e − ORR activity, the atomically dispersed Rh catalyst showed the best activity. Our general approach to atomically dispersed precious metal catalysts may help in understanding their unique catalytic behaviors for the ORR.

Atomically dispersed Lewis acid sites boost 2-electron oxygen reduction activity of carbon-based catalysts

“…This process requires large-scale production equipment, and further transportation requires handling of large amounts of unstable and hazardous solutions 5 . Thus, the usage of an electrochemical oxygen reduction reaction (ORR) through a 2-electron pathway to produce H 2 O 2 is a highly desirable method that can be safe, on-site, portable, and green 6 – 21 . However, this method critically requires the development and screening of low-cost and high-performance electrocatalysts.…”

Recent Progress of Single‐atom Catalysts in the Electrocatalytic Reduction of Oxygen to Hydrogen Peroxide

“…The resulting Pt SACs showed a high activity (3.10 A mg À 1 Pt ) and selectivity (~95 %) towards H 2 O 2 production in 0.1M KOH. In another study, Kim et al [59] developed a general route based on SiO 2 coating to synthesize SACs of various noble metals (i. e., Os, Ru, Rh, Ir and Pt) supported on carbon nanotubes (CNTs) (Figure 2a-c). They first coated CNT with an ionic liquid (IL) containing the metal precursors and annealed the sample at 450°C.…”

Seemingly Negligible Amounts of Platinum Nanoparticles Mislead Electrochemical Oxygen Reduction Reaction Pathway on Platinum Single‐Atom Catalysts

“…Recently, Pt SACs have received much attention as a way to dramatically reduce Pt use in PEMFCs . The ORR follows either a two‐electron pathway (O 2 (g)+2H + (aq)+2e − →H 2 O 2 (aq), E° =+0.690 V) or a four‐electron pathway (O 2 (g)+4H + (aq)+4e − →2H 2 O (l), E° =+1.229 V) . Most Pt SACs reported so far have followed the two‐electron pathway, producing H 2 O 2 .…”

“…Highly oxidic Pt single‐atoms formed on N‐doped carbon support do not show high activity for ORR, following the two‐electron pathway. Many other works have also confirmed that Pt single‐atoms on doped carbon supports followed the two‐electron pathway, while the corresponding Pt nanoparticles followed the four‐electron pathway . However, we do not intend to insist that ORR will not follow the four‐electron pathway for all Pt single‐atoms.…”