Internationale Ausgabe: DOI: 10.1002/anie.201611532 Fuel Cells Hot Paper Deutsche Ausgabe: DOI: 10.1002/ange.201611532 Carbon-Nanotube-Supported Bio-Inspired Nickel Catalyst and Its Integration in Hybrid Hydrogen/Air Fuel Cells Solne Gentil, NoØmie Lalaoui, Arnab Dutta, Yannig Nedellec, Serge Cosnier, WendyJ. Shaw,* Vincent Artero,* and Alan Le Goff* Abstract: A biomimetic nickel bis-diphosphine complex incorporating the amino acid arginine in the outer coordina- tion sphere was immobilized on modified carbon nanotubes (CNTs) through electrostatic interactions. The functionalized redox nanomaterial exhibits reversible electrocatalytic activity for the H 2 /2 H + interconversion from pH 0 to 9, with catalytic preference for H 2 oxidation at all pH values. The high activity of the complex over a wide pH range allows us to integrate this bio-inspired nanomaterial either in an enzymatic fuel cell together with a multicopper oxidase at the cathode, or in a proton exchange membrane fuel cell (PEMFC) using Pt/C at the cathode. The Ni-based PEMFC reaches 14 mW cm 2 , only six-times-less as compared to full-Pt conventional PEMFC. The Pt-free enzyme-based fuel cell delivers  2 mW cm 2 , a new efficiency record for a hydrogen biofuel cell with base metal catalysts. Hydrogenases (H 2 ases) interconvert protons and H 2 rever- sibly, close to the thermodynamic equilibrium. They operate in both directions, although they can be biased to H 2 production or H 2 oxidation. [1–4] When immobilized on electro- des, [5–9] they typically display high turnover frequencies (TOFs) at low overpotential. [10, 11] H 2 ases are generally sensitive to O 2 [12, 13] but, thanks to oxygen-protection strat- egies, were successfully integrated in enzymatic hydrogen fuel cells, together with multicopper oxidases used as O 2 -reducing cathode catalysts. [14–16] However, the complexity of their catalytic site makes them expensive to produce, fragile, and only active under restricted conditions (25–40 8C, pH 4–8). One strategy to overcome the instability of enzymes while using base metal catalysts is the development of bio-inspired iron and/or nickel-based catalysts. [17, 18] The goal is to imitate the function of the active center of the enzyme in order to: 1) reduce its complexity to provide easy and cheap catalyst production and integration; 2) create facile direct electron transfer between the complex and the electrode surface; and 3) enhance the operating stability in a broader chemical space. In that perspective, the series of mononuclear nickel bis-diphosphine complexes, [Ni(P R 2 N R’ 2 ) 2 ] 2+ designed by the DuBois group, [2] forms a unique class of reversible electro- catalysts for the interconversion of H 2 /2 H + . They contain 1,5- diaza-3,7-diphosphacyclooctane (P R 2 N R’ 2 ) ligands, mimicking the 2-azapropanedithiolate found at the active site of [FeFe] hydrogenases. These bis-diphosphine ligands provide the nickel center with an electron-rich environment, while the pendant amine groups act as proton relays in the catalytic cycle. [1, 19] Modification of the R and R’ groups of the P R 2 N R’ 2 ligands enables tuning catalytic preference towards hydrogen oxidation or production. [2, 3, 19] The recent introduction of enzyme-like functionality, such as amino acids [20, 21] or pep- tides, [22] into the outer coordination sphere of such Ni catalysts has resulted in [Ni II (P Cy 2 N Arg 2 ) 2 ] 7+ (1), the most active nickel complex for H 2 oxidation in the series. Complex 1 has a TOF of 210 s 1 in aqueous solution under 1 atm H 2, and 10 6 s 1 under 100 atm of H 2 at 72 8C. [23] The functional groups introduced by the arginine are also proposed to contribute to the enzyme-like reversibility observed over a large pH range at elevated temperature ( 50 8C). [24] While there have been several studies of these complexes bound to surfa- ces, [25, 26] direct comparison of the behavior of the complexes on the surface and in solution has been limited. [27] This comparison is needed as the community takes the growing number of non-precious metal molecular complexes and begins to implement them in devices [28] to develop realistic alternatives to platinum. Herein, we show that electrostatic interactions allow the immobilization of 1 onto single-walled CNTs (SWCNTs) covalently modified with naphthoic acid groups. The resulting material displays redox processes close to the H + /H 2 thermo- dynamic equilibrium over a wide range of pH values, with reversible catalysis being observed at pH 0.3, observations that are interpreted on the basis of proton-coupled electron transfer (PCET) processes. Such properties allowed us to integrate this anode catalyst in a functional hybrid bio- inspired H 2 biofuel cell operating in near-neutral pH and a PEMFC, with multicopper enzyme and Pt/C as cathode O 2 reduction catalysts, respectively. SWCNTs were covalently modified using 2-amino-6- naphthoic acid using a previously described homogenous [*] S. Gentil, Dr. N. Lalaoui, Y. Nedellec, Dr. S. Cosnier, A. LeGoff Univ. Grenoble Alpes, CNRS, DCM UMR 5250 38000 Grenoble (France) E-mail: alan.le-goff@univ-grenoble-alpes.fr S. Gentil, Dr. V. Artero Laboratoire de Chimie et Biologie des MØtaux Univ. Grenoble Alpes, CNRS UMR5249, CEA 38000 Grenoble (France) E-mail: vincent.artero@cea.fr A. Dutta, Dr. W. J. Shaw Pacific Northwest National Laboratory Richland, WA 99532 (USA) E-mail: wendy.shaw@pnnl.gov A. Dutta Current address: Chemistry Department, IIT Gandhinagar Gujarat 382355 (India) Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under http://dx.doi.org/10.1002/anie.201611532. A ngewandte Chemi e Zuschriften 1 Angew. Chem. 2017, 129,1–6  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü