Pyrolyzed Copper-Based Catalyst with High Oxygen Reduction Activity for PEM Fuel Cell Applications

Abstract

We have synthesized a copper-based catalyst for the oxygen reduction reaction in low temperature fuel cells. Catalysts were prepared by covalently attaching a phthalocyanine-type ligand to a carbon black surface, and adding Cu(OAc) 2 . The phthalocyanine-type ligand provides the nitrogen to form the presumed catalytic centers with the Cu metal. Rotating ring disk electrode experiments revealed that the catalytic activity of the as-synthesized material is greatly enhanced after one-step pyrolysis under inert atmosphere, reaching an onset potential of 0.82 V vs. RHE in acidic environment after thermal treatment at 950 • C, making this the best copper-based ORR catalyst in acid reported to date. State of the art proton exchange membrane fuel cells (PEMFCs) use Pt as the catalyst for oxygen reduction reaction (ORR) at the cathode. Due to the high cost of Pt, minimizing the Pt content of the PEMFC has become a major endeavor to make feasible the mass commercialization of PEMFC.1 While a number of efforts seek to achieve this by improving the activity and utilization of Pt-based catalysts, the most direct approach is replacing Pt with non-precious metal catalysts (NPMC). Synthesis of NPMCs is often inspired by natural systems:2 enzymes, such as laccase, are very efficient ORR catalysts. Such Cu oxidases are known to reduce oxygen at approximately 1.2 V vs. the reversible hydrogen electrode (RHE) under mild pH conditions.2-4 The ORR in these enzymes is known to occur in a three or four Cu-atom active site. 4 Since Jasinski first reported the use of Co-phthalocyanine as a catalyst for ORR, 5 a prolonged effort has been devoted to developing ORR catalyst materials based on transition metal complexes. The best NPMCs to date are based on Fe and Co, and can be unsupported 6 or supported on carbon. 7,8 In general their synthesis requires a nitrogen source (nitrogen containing molecule and/or reactive gas) and heat-treatment at high temperatures to form the presumed Me-N 2 and Me-N 4 ORR catalytic centers. After pyrolysis, the precise nature and loading of the catalytic centers are unknown. Though seemingly critical to rational development of new catalysts, the actual active structure is still the subject of speculation, uncertainty and debate.7-14 However, some significant correlative information providing insight into the most favorable nitrogen arrangement has been achieved through the systematic application of XPS methods. From this, it is suggested that the eventual formation of pyridinic nitrogen centers is associated with many successful pyrolysis attempts.Compared to Fe and Co based materials, few studies have been done on ORR using Cu-based catalysts in acidic environments. At low pH values, previous reported Cu-based catalysts exhibit overpotentials for ORR in excess of 600 mV.13,15-21 However, in alkaline media Cubased catalysts show higher catalytic activity, making them suitable for a wide range of applications as ORR catalysts.3,14,20-22 Gewirth's group has adsorbed Cu-based catalysts onto a carbon support and s...

Intercalation of Copper Phthalocyanine Within Bulk Graphite as a New Strategy Toward the Synthesis of CuO-Based CO Oxidation Catalysts

“…There is to our knowledge no example of direct chemical deposition of CuPc on low surface area, bare hydrophobic graphite via non-covalent interactions. Besides, the reported carbon-supported CuPc are either used as such, i.e., with no further transformation of the immobilized CuPc complex (Pakapongpan et al, 2014;Reis et al, 2014;Bian et al, 2020), or after pyrolysis at high temperatures to modify the carbon support (Ding et al, 2012;Goenaga et al, 2014). Their main applications are electrochemistry (Ding et al, 2012;Goenaga et al, 2014;Pakapongpan et al, 2014;Reis et al, 2014;Bian et al, 2020) and photocatalysis (Mukherjee et al, 2017).…”

Patterning Cu nanostructures tailored for CO2 reduction to electrooxidizable fuels and oxygen reduction in alkaline media

“…28,29,[32][33][34][35] It was demonstrated that the morphology and therefore the electrocatalytic properties of Cu nanostructures towards the CO 2 RR can be tuned by the addition of phosphate and the electrodeposition potential 35 or appropriate selection of the Cu complex precursor. 34 Copper-based materials also exhibit electrocatalytic properties towards the ORR 36 and are considered as a replacement for platinum. 37,38 A low overpotential of the ORR in alkaline media with Cu nanoparticles 39 and nanoowers 40 was reported.…”

Oxygen Reduction Reaction Catalyzed by Self-Assembled Monolayers of Copper-Based Electrocatalysts on a Polycrystalline Gold Surface

“…[11][12][13][14] MCOs have a multi-nuclear copper complex at the reaction center and this core structure inspires us to synthesize copper-based ORR catalysts. [15][16][17][18][19][20][21][22][23][24] An intriguing example of copper-based ORR catalysts is a dinuclear copper(II) complex of 3,5-diamino-1,2,4-triazole (Cu-Hdatrz). 20,25 Cu-Hdatrz supported on carbon black shows high ORR activity in the copper-based electrocatalysts (Eonset for ORR = 0.73 V vs pH 7) 20 and its ORR activity increases with increasing pH because of the faster ORR kinetics in basic solutions revealed by in situ X-ray absorption fine structure (XAFS) spectroscopy.…”

“…Thus, simple model systems, for example, two-dimensional systems, will allow us to simplify the electrode preparation process or to obtain mechanistic insights into the reaction mechanism or mass transport of oxygen or proton. 23,[27][28][29] Herein we report two-dimensional model systems to easily study the catalytic activity or oxygen transport of dinuclear copper-based ORR catalysts, which are based on Cu-Hdatrz. We have self-assembled heteroaromatic thiols (Chart 1) and then formed the copper-based ORR catalysts onto a polycrystalline gold surface.…”