TY - JOUR
T1 - Unifying Concepts in Electro- And Thermocatalysis toward Hydrogen Peroxide Production
AU - Adams, Jason S.
AU - Kromer, Matthew L.
AU - Rodríguez-López, Joaquín
AU - Flaherty, David W.
N1 - Publisher Copyright:
© 2021 American Chemical Society.
PY - 2021/6/2
Y1 - 2021/6/2
N2 - We examine relationships between H2O2 and H2O formation on metal nanoparticles by the electrochemical oxygen reduction reaction (ORR) and the thermochemical direct synthesis of H2O2. The similar mechanisms of such reactions suggest that these catalysts should exhibit similar reaction rates and selectivities at equivalent electrochemical potentials (μ¯ i), determined by reactant activities, electrode potential, and temperature. We quantitatively compare the kinetic parameters for 12 nanoparticle catalysts obtained in a thermocatalytic fixed-bed reactor and a ring-disk electrode cell. Koutecky-Levich and Butler-Volmer analyses yield electrochemical rate constants and transfer coefficients, which informed mixed-potential models that treat each nanoparticle as a short-circuited electrochemical cell. These models require that the hydrogen oxidation reaction (HOR) and ORR occur at equal rates to conserve the charge on nanoparticles. These kinetic relationships predict that nanoparticle catalysts operate at potentials that depend on reactant activities (H2, O2), H2O2 selectivity, and rate constants for the HOR and ORR, as confirmed by measurements of the operating potential during the direct synthesis of H2O2. The selectivities and rates of H2O2 formation during thermocatalysis and electrocatalysis correlate across all catalysts when operating at equivalent μ¯ i values. This analysis provides quantitative relationships that guide the optimization of H2O2 formation rates and selectivities. Catalysts achieve the greatest H2O2 selectivities when they operate at high H atom coverages, low temperatures, and potentials that maximize electron transfer toward stable OOH∗ and H2O2∗ while preventing excessive occupation of O-O antibonding states that lead to H2O formation. These findings guide the design and operation of catalysts that maximize H2O2 formation, and these concepts may inform other liquid-phase chemistries.
AB - We examine relationships between H2O2 and H2O formation on metal nanoparticles by the electrochemical oxygen reduction reaction (ORR) and the thermochemical direct synthesis of H2O2. The similar mechanisms of such reactions suggest that these catalysts should exhibit similar reaction rates and selectivities at equivalent electrochemical potentials (μ¯ i), determined by reactant activities, electrode potential, and temperature. We quantitatively compare the kinetic parameters for 12 nanoparticle catalysts obtained in a thermocatalytic fixed-bed reactor and a ring-disk electrode cell. Koutecky-Levich and Butler-Volmer analyses yield electrochemical rate constants and transfer coefficients, which informed mixed-potential models that treat each nanoparticle as a short-circuited electrochemical cell. These models require that the hydrogen oxidation reaction (HOR) and ORR occur at equal rates to conserve the charge on nanoparticles. These kinetic relationships predict that nanoparticle catalysts operate at potentials that depend on reactant activities (H2, O2), H2O2 selectivity, and rate constants for the HOR and ORR, as confirmed by measurements of the operating potential during the direct synthesis of H2O2. The selectivities and rates of H2O2 formation during thermocatalysis and electrocatalysis correlate across all catalysts when operating at equivalent μ¯ i values. This analysis provides quantitative relationships that guide the optimization of H2O2 formation rates and selectivities. Catalysts achieve the greatest H2O2 selectivities when they operate at high H atom coverages, low temperatures, and potentials that maximize electron transfer toward stable OOH∗ and H2O2∗ while preventing excessive occupation of O-O antibonding states that lead to H2O formation. These findings guide the design and operation of catalysts that maximize H2O2 formation, and these concepts may inform other liquid-phase chemistries.
UR - http://www.scopus.com/inward/record.url?scp=85107711761&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85107711761&partnerID=8YFLogxK
U2 - 10.1021/jacs.0c13399
DO - 10.1021/jacs.0c13399
M3 - Article
C2 - 34019397
AN - SCOPUS:85107711761
SN - 0002-7863
VL - 143
SP - 7940
EP - 7957
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 21
ER -