From Food Waste to Efficient Bifunctional Nonprecious Electrocatalyst

Abstract

Synergy between graphitic nanocarbon, obtainable from food waste through cracking of biomethane, and iron oxide nanoparticles provides access to efficient bifunctional electro catalysts. Dissolution of potassium-intercalated graphitic nanocarbons yields graphenide solutions with calibrated, small lateral size-reduced graphenes that are used subsequently as reducing agents of iron metal salts. This results in the strong binding of small size (2-5 nm) nanoparticles on the carbon framework homogeneously within the composite material, accessibility of the catalytic centers, and good conductivity provided by the underlying carbon framework. The iron oxide nanocarbon electrocatalyst performances are highlighted by the overall overpotential of approximately 1 V needed to reach the benchmark threshold of 10 mA cm for the oxygen reduction reaction and the particular activity towards oxygen evolution reaction (η≈0.4 V at 10 mA cm ), comparable to that of the precious RuO and IrO catalysts. This iron oxide/nanocarbon electrocatalyst is versatile, remarkably active, stable, and truly sustainable.

Graphenide Solutions: A Chemical Platform for Nanoparticle–Nanocarbon Composites

“…[1,3,15] Moreover,t he size distribution of the nanoparticlesa re in the range of 1-10 nm. The synthesis afforded the composite materials with good yields of the different metal oxides in the composite materials of about 4.0 at %, as uitable loading for electrocatalysis.…”

“…[10] This is commonly related to the materialp roperties,s uch as high surfacea rea, high chemical stability, and high porosity of the framework,a sw ella st ot he synergistic interactionb etween the active centers and the carbonf ramework. [15] The underlying strategy involves the exploitation of synthetic, sustainable, almost defect-free graphitic nanocarbons, [16,17] generated through plasmas plitting of biomethane, followed by intercalation with potassium metal and dissolution to graphenide solutions (for experimental details see the Supporting Information and SchemeS1). [13,14] Synthetic protocols involvem ixingo ft he metalp recursor,t he respective carbond ispersion, and ar educing agent.…”

“…[11,12] Furthermore, graphene is an excellent support for electrocatalysts due to its highe lectronic conductivity and low charge transfere nergy.C ommonly,w et chemical synthesis of metal-nanoparticle-graphene compositem aterials relies either on graphene oxide or on surfactant-stabilized fewlayer graphene. [18] These were shown to be excellent reducing agentsf or iron salts benefiting from several advantages: [15] 1) formation of nanoparticles in the range of 2-5nmd irectly on the carbon framework, 2) self-limitingr eaction due to the finite amount of electrons, 3) absence of additional stabilizing agentso rf urther reducing agents, 4) grafting of the nanoparticles onto the carbon framework, resulting in strong binding thereof. The particles are first synthesizedi ns olution and subsequently adsorbed on the substrate.…”

“…Notably,t he atomicp ercentages of the different metals under study, calculated from the amount of residue after TGA measurements, were found to be between 3.7 and 4.4 at % (Table ST2, Supporting Information). [15] Scheme1.Reactionofe quimolar amountso fdifferent metal chloride salts (Ni, Mn, Cu, Co) with graphenide solutions forming the respective metal oxiden anoparticles on the carbon scaffold after aqueousw orkup( complete reaction schemei nthe SupportingInformation). [15] Scheme1.Reactionofe quimolar amountso fdifferent metal chloride salts (Ni, Mn, Cu, Co) with graphenide solutions forming the respective metal oxiden anoparticles on the carbon scaffold after aqueousw orkup( complete reaction schemei nthe SupportingInformation).…”

Carbon supported noble metal nanoparticles as efficient catalysts for electrochemical water splitting

“…29,30 This approach allows to graft small and size calibrated nanoparticles randomly distributed onto the carbon frameworks by simultaneously controlling the grafting ratio and the respective size distribution. 31,32 This control is achieved by the exploitation of the graphenide solution as the reduction agent as the redox process can take place only in the proximity of the carbon lattice and because the number of electrons on the carbon lattice is finite. This modular approach permits the accessibility of the catalytic centers by simultaneously maintaining the conductivity of the carbon lattice.…”