| With the development of human society and increasing energy demand, the energy crisis has become ahuge challenge facing the world. Simultaneously, the excessive use of fossil fuels has caused a series ofenvironmental problems. Searching environmentally-friendly, high efficient, low cost and sustainable ofnew energy has become a major issue of the world. At present, the production and utilization of fuel cell isone of the hot research areas of global concern. Insufficient activities and high cost of electrodes material offuel cell are the major challenges hindering its commercialization. Seeking the high performance, low costelectrode materials and in-depth understanding of chemical reaction mechanisms on it, has a decisive rolefor to search new electrode materials.In this work, we used a slab model and the density functional theory (DFT) method to investigateoxygen reduction reaction (ORR) and dissociation of water on the Pt monolayer surfaces modified by a lowcost subsurface WC material. We investigated the structure of Pt/WC electrodes and ORR mechanisms, anddiscussed the confinement effects on H2O dissociation for the process of H2O reused. The results aresummarized as follows:(1) We calculated the geometric and electronic of Pt/WC system with the Pt monolayer respectivelydeposit in W-and C-terminated WC(0001) surface (denoted PtML/C-WC(0001) and PtML/W-WC(0001),respectively), and compared with the Pt(111) surface. The results showed that Pt priority deposit in hcppositions of the two different atom terminated WC surfaces, and the electronic structure of the two surfacessimilar to the Pt(111) surface. The Pt monolayer of Pt/WC has high stability, and PtML/W-WC(0001)compared with PtML/C-WC(0001) or Pt(111) are more stable, indicating that performance of Pt/WC as theelectrode material is very excellent.(2) For the ORR, we studied three possible mechanisms: oxygen dissociation mechanism, peroxyldissociation mechanism and hydrogen peroxide dissociation mechanism. The results revealed that, ORRadopted the peroxyl dissociation mechanism on the PtML/W-WC(0001) surface, the process through foursteps as follows:(a) O2+Hâ†'O2H,(b) O2Hâ†'O+OH,(c) O+Hâ†'OH,(d) OH+Hâ†'H2O, where (d)step is the rate-determining step with an activation energy of0.55eV. ORR adopted oxygen dissociation mechanism on PtML/C-WC(0001) surface, steps as follows:(a) O2â†'2O，(b) O+Hâ†'OH，(c) OH+Hâ†'H2O，(b) is the rate-determining step with an activation energy of1.28eV. If H2O adsorbed on the surface,O+H2Oâ†'2OH, the rate-determining step is (c) with an activation energy of1.18eV. Compared to thetwo surface, the activation performance on PtML/W-WC(0001) surface is better. Electric field and solventeffect unchanged the ORR mechanism on PtML/W-WC(0001) surface, but the presence of H2O reduces theactivation energy of elementary reaction steps for ORR.(3) On the surface, the adsorption of H2O molecules with low coverage is weak. With the decrease ofthe a surface-surface separation, the binding energy of H2O on the PtML/WC(0001) surface graduallyincreased and reach the maximum when surface-surface separation is reduced to5.66. Confinementeffects will make for dissociation of H2O, the coexistence of H2O molecules has a catalytic action for thedissociation of H2O. Under systems confinement on the PtML/WC(0001) surface, H2O dissociationmechanism as follows:(a)2H2Oâ†'H2O+OH+H，(b) H2O+OHâ†'2OH+H，(c)2OHâ†'O+H2O，(d)2Oâ†'O2，where (b) is the rate-determining. |
PDF Full Text Request