Hydrogen and Chemicals from Renewable Alcohols by Organometallic Electroreforming

Abstract

The selectivea nd simultaneous productiono fh ydrogen and chemicals from renewable alcohols was accomplished by using an electrolyzer,f or which the anode electrocatalyst was an organometallic complex, [Rh(OTf)(trop 2 NH){P(4-BuC 6 H 4 ) 3 }] (trop 2 NH = bis(5H-dibenzo[a,d]cyclohepten-5-yl)amine; À OTf = CF 3 SO 3 À ), deposited on amorphous carbon and appropriately designed to promote the partial and selective oxidation of alcohols. The electrolyzer converted alcohols into industriallyr elevant chemicals and high-purity hydrogen at high volume and with very low energy consumption.[b] Q. HeSupporting Information and the ORCID identification number(s) for the author(s) of this article can be found under: http://dx.

Energy Production and Storage Promoted by Organometallic Complexes

“…Vizza, Grützmacher et al synthesized the complex [Rh(OTf)(trop 2 NH)P(4‐ n ‐butyl‐Ph) 3 ] [trop 2 NH = bis(5‐H dibenzo[a,d]cyclohepten‐5‐yl)‐amine OTf – = CF 3 SO 3 – = triflate] that was dispersed on high surface area carbon black Ketjenblack EC‐600JD to obtain an electrode whose activity was tested by cyclic voltammetry in 2 m alcohol 2 m KOH solutions . To the best of our knowledge, this electrocatalyst has the highest mass activity ever reported in literature for ethanol electrooxidation: 16000 Ag Rh –1 at 1.2 V vs. RHE, a value even higher than the mass activity of the state‐of‐the‐art nanostructured palladium based electrocatalysts , . This rhodium complex has the capability to oxidize several renewable alcohols and diols, such as ethanol, 1,2‐propanediol and glycerol, in a wide potential window (from 0.65 V to 1.2 V vs. RHE).…”

“…The complex is stable even at high potentials and its activity for the oxidation of several substrates makes it a good candidate as anodic electrocatalyst for direct alcohol fuel cells and alcohol electroreformers. In fact, it represents one of the few examples of organometallic‐based anodes that have been successfully assembled in a complete cell; this aspect will be described in detail in sections four and five , , , …”

“…The Department of Energy of the United States of America stated that to make economically appealing H 2 production from electrolysis, the electrical energy input to the electrolyzer stacks should drop from 45 to 43 kWh kg –1 H2 by 2020 . The replacement of the thermodynamic unfavorable water oxidation reaction, which occurs at the anode of the electrolytic cell, with the oxidation of a soluble substrate whose oxidation potential is much lower than that of water, is a strategy for lowering the energetic costs of electrolysis of an aqueous fuel , . Several compounds have been employed as anodic sacrificial molecules, e.g.…”

“…In the previous section, we reported some examples of Ni and Mo complexes that convert protons into hydrogen with high turnovers but for the oxidation of alcohols at the anodic side, the only example reported to date are the rhodium complexes of type [Rh(trop 2 N)(PR 3 )] developed by Grützmacher and Vizza in 2012 . Again the precursor complex [Rh(OTf)(trop 2 NH){P(4‐ n ‐butyl‐Ph) 3 }] [trop 2 NH = bis(5‐H dibenzo[a,d]cyclohepten‐5‐yl)‐amine; OTf – = CF 3 SO 3 – = triflate] was supported onto carbon black Ketjenblack EC 600JD ( 1@C in Figure ) to create an Organo Metallic Electro Reformer (OMER) . The originality of the idea is to couple the anodic oxidation of alcohols promoted by this organometallic compound, , with the cathodic hydrogen evolution reaction (Figure ).…”

“…Scheme of the OMER cell and the proposed mechanism for the alcohols oxidation reactions occurring on the anode. Reproduced from ref …”