Electrochemical formic acid oxidation catalyzed by graphene supported bimetallic Pd-Ni clusters: The role of Ni content and the hydrogen effect

By means of periodic density functional theory calculations, we have investigated the electrocatalytic formic acid oxidation (FAO) on graphene supported Pd-Ni catalysts and elucidate the detail about the role of Ni content in different Pd-Ni atomic ratio and the hydrogen coverage effect. The FAO reaction often onsets at low oxidation potential range, where deposition of hydrogen is alive and affect the catalytic performance of Pd-Ni clusters, accordingly, the FAO reaction on varied H* ratio Pd-Ni clusters accompanying with enhanced external potential is also considered. In our calculation, the H* saturated situation would suppress the formation of COOH* much more than that of HCOO*, even controlling the reaction energy of HCOO* from HCOOH become moderate in FAO reaction. In addition, the potential requirements to proceed the FAO reaction on Pd10-gra and Pd8Ni2- graphene are similar but Ni content could also suppress formation of COOH* and enhance the interaction be-tween Pd8Ni2-graphene and HCOO* species. Pd6Ni4-grahene model is another choice for FAO reaction, in which the HCOO* species on clean Pd6Ni4-graphene model has lowest onset potential of 0.18 V for HCOO* deproto-nation to CO2 in all of our models. However, excess Ni content would cause Ni exposed on Pd2Ni8-grahene, where the HCOO* is downhill in energy with a larger onset potential of 0.59 V for the deprotonation of HCOO*, but the hydride formation of 8H* and 9H* Pd2Ni8-graphene could overcome the question.