REFERENCES
(1) Li, N.; Tang, S.; Meng, X. Reduced graphene oxide supported bimetallic cobalt-palladium nanoparticles with high catalytic activity towards
  formic acid electro-oxidation. J. Mater. Sci. Technol. 2015, 31, 3036.
(2) Baik, S. M.; Han, J.; Kim, J.; Kwon, Y. Effect of deactivation and reactivation of palladium anode catalyst on performance of direct formic acid
fuel cell (DFAFC). Int. J. Hydrogen Energ. 2011, 36, 1471914724.
(3) Kim, Y.; Kim, H. J.; Kim, Y. S.; Choi, S. M.; Seo, M. H.; Kim, W. B. Shape- and composition-sensitive activity of Pt and PtAu catalysts for
formic acid electrooxidation. J. Phys. Chem. C 2012, 116, 1809318100.
(4) Shi, M.; Liu, W.; Zhao, D.; Chu, Y.; Ma, C. A. Synthesis of palladium nanoparticles supported on reduced graphene oxide-tungsten carbide
composite and the investigation of its performance for electrooxidation of formic acid. J. Solid State Electr. 2014, 18, 19231932.
(5) Rees, N. V.; Compton, R. G. Sustainable energy: a review of formic acid electrochemical fuel cells. J. Solid State Electr. 2011, 15, 20952100.
(6) Zhang, W.; Yao, Q.; Wu, X.; Fu, Y.; Deng, K.; Wang, X. Intimately coupled hybrid of graphitic carbon nitride nanoflakelets with reduced
graphene oxide for supporting Pd nanoparticles: a stable nanocatalyst with high catalytic activity towards formic acid and methanol electrooxidation. Electrochim. Acta 2016, 200, 131141.
(7) Zhong, J.; Bin, D.; Ren, F.; Wang, C.; Zhai, C.; Yang, P.; Du, Y. Graphene nanosheet-supported Pd nano-leaves with highly efficient
electrocatalytic performance for formic acid oxidation. Colloid. Surf. A Physicochem. Eng. Asp. 2016, 488, 16.
(8) Zhao, X.; Zhu, J.; Liang, L.; Liu, C.; Liao, J.; Xing, W. Enhanced electroactivity of Pd nanocrystals supported on H3PMo12O40/carbon for
formic acid electrooxidation. J. Power Sources 2012, 210, 392396.
(9) Haan, J. L.; Stafford, K. M.; Masel, R. I. Effects of the addition of antimony, tin, and lead to palladium catalyst formulations for the direct
    formic acid fuel cell. J. Phys. Chem. C 2010, 114, 1166511672. 
(10) Yu, X.; Pickup, P. G. Mechanistic study of the deactivation of carbon supported Pd during formic acid oxidation. Electrochem. Commun. 2009,
    11, 20122014.
(11) Feng, L.; Sun, X.; Liu, C.; Xing, W. Poisoning effect diminished on a novel PdHoOx/C catalyst for the electrooxidation of formic acid. Chem.
    Commun. 2012, 48, 419421. 
(12) Keita, B.; Nadjo, L. Polyoxometalate-based homogeneous catalysis of electrode reactions: recent achievements. J. Mol. Catal. a-Chem. 2007,
262, 190215.
(13) Sadakane, M.; Steckhan, E. Electrochemical properties of polyoxometalates as electrocatalysts. Chem. Rev. 1998, 98, 219237. 
(14) Zhang, X.; Wang, X.; Le, L.; Ma, A.; Lin, S. A Pd/PW12/RGO composite catalyst prepared by electro-codeposition for formic acid electro-
oxidation. J. Electrochem. Soc. 2016, 163, 7178. 
(15) Kovalchuk, T. V.; Sfihi, H.; Zaitsev, V. N.; Fraissard, J. Preparation and characterization of catalysts based on oniumsilica-immobilized keggin
acids. Catal. Today 2011, 169, 138149.
(16) He, X.; Chen, L.; Li, Z.; Zhang, X.; Ma, A.; Lin, S. Enhanced electrocatalysis for methanol oxidation on ordered {PdPW11O39 (5-)/Pt/PAMAM)(n)}
multilayer composites. Fuel Cells 2015, 15, 221229.
(17) Liu, M. M.; Zhang, R. Z.; Chen, W. I. Graphene-supported nanoelectrocatalysts for fuel cells: synthesis, properties, and applications. Chem
. Rev. 2014, 114, 51175160.
(18) She, Y.; Lu, Z.; Fan, W.; Jewell, S.; Leung, M. K. H. Facile preparation of PdNi/rGO and its electrocatalytic performance towards formic acid
oxidation. J. Mater. Chem. A 2014, 2, 38943898. 
(19) Cui, Y.; Zhou, D.; Sui, Z.; Han, B. Sonochemical synthesis of graphene oxide-wrapped gold nanoparticles hybrid materials: visible light
photocatalytic activity. Chin. J. Chem. 2015, 33, 119124.
(20) Guo, S.; Wen, D.; Zhai, Y.; Dong, S.; Wang, E. Platinum nanoparticle ensemble-on-graphene hybrid nanosheet: one-pot, rapid synthesis, and
    used as new electrode material for electrochemical sensing. Acs Nano. 2010, 4, 39593968.
(21) Sattayasamitsathit, S.; Gu, Y.; Kaufmann, K.; Jia, W.; Xiao, X.; Rodriguez, M.; Minteer, S.; Cha, J.; Burckel, D. B.; Wang, C.; Polsky, R.;
Wang, J. Highly ordered multilayered 3D graphene decorated with metal nanoparticles. J. Mater. Chem. A 2013, 1, 16391645.
(22) Paredes, J. I.; Villar-Rodil, S.; Fernandez, M. M. J.; Guardia, L.; Martinez, A. A.; Tascon, J. M. D. Environmentally friendly approaches
toward the mass production of processable graphene from graphite oxide. J. Mater. Chem. 2011, 21, 298306.  
(23) Reybier, K.; Malugani, J. P.; Fantini, S.; Herlem, M.; Fahys, B. Electrodeposition of keggin-type heteropolyanions on different electrode
surfaces from nonaqueous media. J. Electrochem. Soc. 2002, 149, 96101.
(24) Wang, S. F.; Du, D. Preparation and electrochemical properties of keggin-type phosphomolybdic anions in electrostaticly linked L-cysteine
self-assembled monolayers, Sensors Actuat. B-Chem. 2003, 94, 282289. 
(25) Wang, X. L.; Han, Z. B.; Wang, E. B.; Zhang, H.; Hu, C. W. A bifunctional electrocatalyst containing tris(2, 2΄-bipyridine) ruthenium(II) and
12-molybdophosphate bulk-modified carbon paste electrode. Electroanal. 2003, 15, 14601464.
(26) Huang, X. L.; Lin, Z.; Lian, X. Y.; Zhang, X. F.; Lin, S. Preparation and electrocatalytic properties of Pd/PMo12-GN composite towards formic
acid oxidation. J. Inorg. Mater. 2014, 29, 722728.
(27) Ma, A.; Zhang, X. F.; Li, Z. S.; Wang, X. Y.; Ye, L. T.; Lin, S. Graphene and polyoxometalate synergistically enhance electro-catalysis of Pd
toward formic acid electro-oxidation. J. Electrochem. Soc. 2014, 161, 12241230.
(28) Whitby, R. L. D. Chemical control of graphene architecture: tailoring shape and properties, Acs. Nano. 2014, 8, 97339754.
(29) Liu, R. J.; Xian, Z. W.; Zhang, S. S.; Chen, C. H.; Yang, Z. H.; Li, H.; Zheng, W. Q.; Zhang, G. G.; Cao, H. B. Electrochemical-reduction-
assisted assembly of ternary Ag nanoparticles/polyoxometalate/graphene nanohybrids and their activity in the electrocatalysis of oxygen reduction. RSC Adv. 2015, 5, 7444774456.
(30) Mendonça, M. C. P.; Soares, E. S.; Jesus, M. B.; Ceragioli, H. J.; Sakane, K. K.; Cruz-Höfling, M. A. Raman spectroscopy as a tool to evaluate
brain tissue composition after administration of reduced graphene oxide. J. Appl. Spectrosc. 2016, 83, 805810.
(31) Ferrari, A. C. Raman spectroscopy of graphene and graphite: disorder, electron-phonon coupling, doping and nonadiabatic effects. Solid State
 Commun. 2007, 143, 4757.
(32) Liu, R.; Li, S.; Yu, X.; Zhang, G.; Zhang, S.; Yao, J.; Keita, B.; Nadjo, L.; Zhi, L. Facile synthesis of Au-
nanoparticle/polyoxometalate/graphene tricomponent nanohybrids: an enzyme-free flectrochemical biosensor for hydrogen peroxide. Small 2012, 8, 13981406.  
(33) Gao, X.; Li, F.; Li, Y.; Li, S.; Chen, Y.; Lee, J. M. A surfactant-free strategy for synthesizing reduced graphene oxide supported palladium
nanoparticles with enhanced electrocatalytic performance towards formic acid oxidation. J. Power Sources 2015, 280, 491498.
(34) Yousaf, A. B.; Imran, M.; Zeb, A.; Xie, X.; Liang, K.; Zhou, X.; Yuan, C. Z.; Xu, A. W. Synergistic effect of graphene and multi-walled
carbon nanotubes composite supported Pd nanocubes on enhancing catalytic activity for electro-oxidation of formic acid. Catal. Sci. Technol. 2016, 6, 47944801.
(35) Wang, D.; Lu, S. F.; Kulesza, P. J.; Li, C. M.; Marcoe, R. D.; Jiang, S. P. Enhanced oxygen reduction at Pd catalyticnanoparticles dispersed
onto heteropolytungstate-assembled poly(diallyldimethylammonium)-functionalized carbonnanotubes. Phys. Chem. Chem. Phys. 2011, 13, 44004410.
(36) Wang, S.; Li, H.; Li, S.; Liu, F.; Wu, D.; Feng, X.; Wu, L. Electrochemical-reduction-assisted assembly of a polyoxometalate/graphene    nanocomposite and its enhanced lithium-storage performance. Chem. Eur. J. 2013, 19, 1089510902.
(37) Li, R.; Wei, Z.; Huang, T.; Yu, A. Ultrasonic-assisted synthesis of Pd–Ni alloy catalysts supported on multi-walled carbon nanotubes for
formic acid electrooxidation. Electrochim. Acta 2011, 56, 68606865.
(38) Bueno, P. R.; Pianaro, S. A.; Pereira, E. C.; Bulhoes, L. O. S.; Longo, E.; Varela, J. A. Investigation of the electrical properties of SnO2 varistor
system using impedance spectroscopy. J. Appl. Phys. 1998, 84, 37003705.
(39) Joshi, P.; Zhang, L. F.; Chen, Q. L.; Galipeau, D.; Fong, H.; Qiao, Q. Q. Electrospun carbon nanofibers as low-cost counter electrode for dye-
sensitized solar cells, ACS Appl. Mater. Interfaces 2010, 2, 35723577.
(40) Li, Y. J.; Gao, W.; Ci, L. J.; Wang, C. M.; Pulickel, M. A. Catalytic performance of Pt nanoparticles on reduced graphene oxide for methanol
electro-oxidation. Carbon 2010, 48, 11241130.
(41) Shen, L. P.; Li, H. Z.; Lu, L.; Luo, Y. F.; Tang, Y. W.; Tian, Y. C.; Lu, H. Improvement and mechanism of electrocatalytic performance of Pd–
Ni/C anodic catalyst in direct formic acid fuel cell. Electrochimica Acta 2013, 89, 497502.