Design And Preparation Of Multi-Component Pd-based Nanoporous Catalyst

Proton exchange membrane fuel cell（PEMFC）can provide cleaning energy with high energy conversion efficiency and therefore is regarded as one of the most promising energy supplies to replace the traditional energy generation.Recently,it has been found that nanoporous Pd alloys exhibit good catalytic activity in PEMFC.Moreover,it has much high CO tolerance than the expensive commercial Pt/C catalysts.However,nanoporous Pd display much lower catalytic activity and structural stability towards the catalysis of the oxygen reduction（ORR）reaction.Therefore,this work intends to improve the catalytic activity and stability by tuning the dealloying parameters and microalloying the nanoporous Pd with Mo/Nb.The main results are summarized as the following:Tuning the dealloying potentials and durations leads to the improvements on catalytic activity of nanoporous Pd towards ORR.The chemical compositions and morphologies of the dealloyed products are strongly dependent on the dealloying potentials when the Pd₂₀Ni₈₀was potentiostatically dealloyed in 1 M H₂SO₄ solution.Pd catalyst with a nanoporous structure can only be obtained when the dealloying potential was near 0.83 V vs RHE.Too high or low potentials simply lead to the formation of a relatively dense Pd-rich passivation layer.The nanoporous Pd prepared under a dealloying potential of 0.83 V vs RHE displays increasing electrochemical active area and roughness with the increase in dealloying time.The sample dealloyed for 9000 s exhibits the most positive ORR half-wave potential(E_1/2)of 0.943 V vs RHE,which is 83 m V more positive than the commercial Pt/C and 146 m V more positive than the commercial Pd/C.However,the electrochemical activity area decreased dramatically by 23%after recycling,which leads to the negative shift of the E_1/2.The nanoporous Pd is doped with Mo/Nb with a high melting temperature to delay the structure coarsening uring catalyzing.The results show that Mo-doped nanoporous Pd can be obtained by dealloying Mo doped Pd₂₀Ni₈₀ prealloys at 0.83 V vs RHE.The electrochemically active area and roughness increased with the prolongation of dealloying time,and the values are equivalent to those of the samples obtained by dealloying Pd₂₀Ni₈₀ under the same conditions.The ORR tests show that the catalytic performance of Mo-doped nanoporous Pd is comparable to that of undoped samples.However,the decrement of the electrochemical area decreased after recycling is much lower.The Nb-doped nanoporous Pd could be obtained by dealloying Nb-doped Pd₂₀Ni₈₀ prealloy at 0.83 V vs RHE.The electrochemically active area and roughness increased with the increase of dealloying time,but the values are lower than that of the Pd₂₀Ni₈₀ dealloyed under the same conditions.The ORR tests show that the catalytic performance and the structure stability of the Nb-doped nanoporous Pd is similar to that of undoped samples.