Activity–Selectivity Trends in the Electrochemical Production of Hydrogen Peroxide over Single-Site Metal–Nitrogen–Carbon Catalysts

Abstract

Nitrogen-doped carbon materials featuring atomically dispersed metal cations (M−N−C) are an emerging family of materials with potential applications for electrocatalysis. The electrocatalytic activity of M−N−C materials toward four-electron oxygen reduction reaction (ORR) to H 2 O is a mainstream line of research for replacing platinumgroup-metal-based catalysts at the cathode of fuel cells. However, fundamental and practical aspects of their electrocatalytic activity toward two-electron ORR to H 2 O 2 , a future green "dream" process for chemical industry, remain poorly understood. Here we combined computational and experimental efforts to uncover the trends in electrochemical H 2 O 2 production over a series of M−N−C materials (M = Mn, Fe, Co, Ni, and Cu) exclusively comprising atomically dispersed M−N x sites from molecular first-principles to bench-scale electrolyzers operating at industrial current density. We investigated the effect of the nature of a 3d metal within a series of M−N−C catalysts on the electrocatalytic activity/selectivity for ORR (H 2 O 2 and H 2 O products) and H 2 O 2 reduction reaction (H 2 O 2 RR). Co−N−C catalyst was uncovered with outstanding H 2 O 2 productivity considering its high ORR activity, highest H 2 O 2 selectivity, and lowest H 2 O 2 RR activity. The activity−selectivity trend over M−N−C materials was further analyzed by density functional theory, providing molecular-scale understandings of experimental volcano trends for four-and two-electron ORR. The predicted binding energy of HO* intermediate over Co−N−C catalyst is located near the top of the volcano accounting for favorable two-electron ORR. The industrial H 2 O 2 productivity over Co−N−C catalyst was demonstrated in a microflow cell, exhibiting an unprecedented production rate of more than 4 mol peroxide g catalyst −1 h −1 at a current density of 50 mA cm −2 .

Metal–Organic Frameworks Based Electrocatalysts for the Oxygen Reduction Reaction

“…Other than highly active sites, the density and utilization rate of active sites, charge transfer, interface properties between different components, electrocatalysts and electrolyte, etc., are all important factors for improving the overall electrocatalytic performance Highly efficient and stable electrocatalysts in acidic media can be realized by incorporation of M‐N‐C moieties or Pt‐based alloys into MOFs, MOF composites, and MOF derivatives The specific requirements of electrocatalysts for practical applications can sometimes be satisfied with the design of catalysts.…”

“…Highly efficient and stable electrocatalysts in acidic media can be realized by incorporation of M‐N‐C moieties or Pt‐based alloys into MOFs, MOF composites, and MOF derivatives …”

“…[87,139] vi)S ystem-level studies would be appreciated for the design and synthesis of highly efficient electrocatalysts.O ther than highly active sites,the density and utilization rate of active sites,c harge transfer, interface properties between different components,e lectrocatalysts and electrolyte,e tc., are all important factors for improving the overall electrocatalytic performance. [140,141] vii)H ighly efficient and stable electrocatalysts in acidic media can be realized by incorporation of M-N-C moieties [90,95,99,142,143] or Pt-based alloys into MOFs, MOF composites,a nd MOF derivatives. [56,106,144] viii)T he specific requirements of electrocatalysts for practical applications can sometimes be satisfied with the design of catalysts.F or example,u niformly tunable pores in MOFs and mesoporous carbon wall in MOF derivatives can provide effective selectivity towards oxygen molecules but largely prevent crossover by contaminants.…”

Stabilizing mechanism of single-atom catalysts on a defective carbon surface

“…Other desirable catalytic properties of SA catalysts include high selectivity, tunable high activity, and unique metal coordination environments [3][4][5][6] . As a result, SA catalysts have attracted tremendous attention as a new frontier in heterogeneous catalysis for many reactions, including oxidation 7,8 , hydrogenation 9,10 , electrocatalysis [11][12][13][14] , and so on 15,16 . However, SAs have the tendency to aggregate into particles at an elevated temperature due to their excess surface-free energy, which is known as thermal deactivation or sintering [17][18][19] .…”

Partially Pyrolyzed Binary Metal–Organic Framework Nanosheets for Efficient Electrochemical Hydrogen Peroxide Synthesis

“…It is well established that the electrochemical H 2 O 2 selectivity is highly determined by the inhibiting ability of the electrocatalyst to break the O À O bond during the ORR, which is further set by the binding strengths of HOO*. [25,26] Hence, the activity and selectivity are both decided by the binding of HOO*, while the binding behavior is influenced by the electronic properties of a catalyst. Among the transition metals, Ni has been shown to possess excellent adsorption ability for O 2 , but the O 2 dissociation readily occurs on monometallic Ni.…”