DOI: 10.1002/celc.201402142 Insights on Hybrid Glucose Biofuel Cells Based on Bilirubin Oxidase Cathode and Gold-Based Anode Nanomaterials Yaovi Holade, [a] Adriana Both Engel, [b] Sophie Tingry, [b] Aziz Cherifi, [b] D. Cornu, [b] Karine Servat, [a] TÞko W. Napporn, [a] and Kouakou B. Kokoh* [a] 1. Introduction Unlike conventional fuel cells (FCs), [1] where size and operating conditions are inappropriate for powering small and in vivo systems, [2] batteries are undoubtedly the first choice of energy source to power microscale devices or electronic medical im- plants. [3] Owing to environmental concerns and recharging delays, numerous efforts have focused on developing alterna- tive systems for energy production that are capable of operat- ing independently over prolonged periods of time, without the need for external recharging or refueling. [4] Over the last few decades, biofuel-cell (BFC) science has received increasing interest with respect to energy-harvesting devices. [4a, 5] Basically, a BFC converts the available free chemical energy of biofuels (stored as chemical bonds in organic molecules) directly into electrical energy. Biofuels such as glucose and other carbohy- drates can be found in vegetables, [6] animals, and human fluid- s. [5a, 6c, 7] In the case of implantable BFCs, in contrast to batteries, constant replenishing of fresh reactants from the body occurs, and this type of BFC is, therefore, theoretically capable of oper- ating indefinitely. [4b] Glucose is one of the most available bio- fuels for BFCs. Recently, the group of Katz has reported the first pacemaker powered by an implantable BFC in lobsters. [7e] This pacemaker system can provide an open circuit voltage (OCV) of 0.8 V and maximum power of 5.2 mW. This pathfinder research group has tested the device with other living systems including snails [8] and clams. [7d] Other BFCs powered by living systems including plants, [6a, b, 9] animals, [7a, c, 9] the brain–machine interface [10] or related human systems [11] have been successfully tested. Fundamentally, oxidation of the fuel is performed at the anode while reduction of molecular oxygen occurs at the cathode, under conditions close to those of living systems. For the oxygen reduction reaction (ORR), several studies have shown that enzymes such as laccase and bilirubin oxidase (BOD) are more active and selective than the state-of-the-art electrocatalyst, platinum. [5b, 12] Moreover, another advantage of the use of enzymes instead of platinum catalysts is the fact that the reaction starts at a higher potential: around 1.2 V versus that of a reversible hydrogen electrode (RHE) compared with 1 V versus RHE on platinum electrode. [12] More important- ly, enzymes promote a four-electron reduction of oxygen, lead- ing directly to water, whereas the use of inorganic catalysts leads to the production of a significant amount of hydrogen peroxide (H 2 O 2 ; two exchanged electrons). [13] Despite all the advantages of the use of enzymes as catalysts, the reason why enzymatic BFCs have not yet been generally adopted commer- cially is the limited enzyme lifetime. [14] Enzyme immobilization techniques are, thus, crucial for increasing the stability of the enzyme, [15] and several immobilization techniques have been studied including physical adsorption, entrapment in gel or polymer matrix, and covalent immobilization. [16] As far as the anode of glucose BFC (GBFC) is considered, glu- cose oxidation catalyzed by glucose oxidase (GOx) or glucose dehydrogenase (GDH) is limited by the regeneration of the enzyme at the anode. Moreover, in the case of GOx, a parasite reaction between glucose and dioxygen catalyzed by GOx gen- We report a straightforward design for a hybrid glucose biofuel cell (h-GBFC) operating at pH 7.4 with 10 mM glucose at 37 8C. Homemade electrospun carbon nanofibers were used as elec- trode support. Clean and highly active gold-based nanomateri- als (3–6 nm) were synthesized for glucose electrooxidation. En- hanced catalytic activity toward glucose oxidation has been highlighted. Bilirubin oxidase enzyme was used to catalyze the oxygen reduction reaction. The constructed h-GBFCs exhibit an unexpected and highly improved open circuit voltage of 0.92 V, which is the best value so far reported for such cells. The abiotic Au 60 Pt 20 Pd 20 /C anode induces high electrical per- formance with a maximum power density of 91 mW cm 2 at 0.365 V. This improvement over monometallic anode catalysts has been assigned to synergistic effects between gold, plati- num, and palladium. Strategies developed herein will serve as guidelines for the development of new rational pathways to more powerful, stable, and promising GBFC designs. [a] Y. Holade, Dr. K. Servat, Dr. T. W. Napporn, Prof. Dr. K. B. Kokoh UniversitØ de Poitiers IC2MP CNRS UMR 7285 4 rue Michel Brunet-B27, TSA 51106 86073 Cedex 9, France E-mail : boniface.kokoh@univ-poitiers.fr [b] A. Both Engel, Dr. S. Tingry, Dr. A. Cherifi, Prof. Dr. D. Cornu Institut EuropØen des Membranes UMR 5635, Place Eugne Bataillon, CC 047 34095 Montpellier, Cedex 5, France Supporting Information for this article is available on the WWW under http ://dx.doi.org/10.1002/celc.201402142. An invited contribution to a Special Issue on Biofuel Cells  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemElectroChem 2014, 1, 1976 – 1987 1976 CHEMELECTROCHEM ARTICLES