Menggai Jiao

High performance platinum single atom electrocatalyst for oxygen reduction reaction

For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm−2 at 80 °C with a low platinum loading of 0.09 mgPt cm−2, corresponding to a platinum utilization of 0.13 gPt kW−1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.

The oxygen reduction reaction on Pt(111) and Pt(100) surfaces substituted by subsurface Cu: a theoretical perspective

The mechanisms of the oxygen reduction reaction (ORR) on Pt/Cu(111) and Pt/Cu(100) have been investigated by using density functional theory. Compared with pure Pt(111) and Pt(100), the adsorptions of ORR intermediates are weakened on both Pt/Cu(111) and Pt/Cu(100) surfaces. The ORR follows the oxygen dissociation mechanism on Pt/Cu(100) which is the same as that on pure Pt(100). However, the ORR mechanism is the peroxyl dissociation mechanism on pure Pt(111), hydrogen peroxide dissociation on Pt/Cu(111). The rate determining step is OH + H+ + e− → H2O on Pt/Cu(100) and pure Pt(100), O + H+ + e− → OH on pure Pt (111) and OOH + H+ + e− → H2O2 on Pt/Cu(111). Compared with the energy barrier of the rate determining step on pure Pt(111) (0.86 eV) and Pt(100) (0.76 eV), the ORR reaction activity is improved on Pt/Cu(111) and hindered on Pt/Cu(100), with the barriers of 0.40 and 0.85 eV, respectively. For the effects of electric potential, OH protonation is favorable thermodynamically at a broad electrode potential (from 0 to 1.23 V) on the Pt/Cu(111) surface, in agreement with the high durability of Pt/Cu observed in experiments. The working potentials of Pt/Cu(111) and Pt/Cu(100) are predicted to be 0.39 and 0.73 V, respectively.

Crystalline Ni3C as both carbon source and catalyst for graphene nucleation: a QM/MD study.

Graphene nucleation from crystalline Ni3C has been investigated using quantum chemical molecular dynamics (QM/MD) simulations based on the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. It was observed that the lattice of Ni3C was quickly relaxed upon thermal annealing at high temperature, resulting in an amorphous Ni3C catalyst structure. With the aid of the mobile nickel atoms, inner layer carbon atoms precipitated rapidly out of the surface and then formed polyyne chains and Y-junctions. The frequent sinusoidal-like vibration of the branched carbon configurations led to the formation of nascent graphene precursors. In light of the rapid decomposition of the crystalline Ni3C, it is proposed that the crystalline Ni3C is unlikely to be a reaction intermediate in the CVD-growth of graphene at high temperatures. However, results present here indicate that Ni3C films can be employed as precursors in the synthesis of graphene with exciting possibility.

A density functional theory study on 3d metal/graphene for the removal of CO from H2 feed gas in hydrogen fuel cells

Metal/graphene has been used as a filter membrane exterior to the hydrogen fuel cell to prevent CO poisoning. The removal of CO from H2 feed gas is important for efficient use of the anode catalyst and would increase the lifetime of the fuel cells. In this work, the adsorptions of CO and H2 on metal/perfect-graphene (M/Gp) and metal/defect-graphene (M/Gd) (M = Sc–Zn) are investigated using density functional theory. Our results indicated that the defect sites in graphene enhance the stability of metal on the graphene surface compared to perfect graphene. For gas molecule adsorption, however, CO and H2 adsorption is weaker on defective graphene compared with the perfect material, due to the more localized metal d electrons in the former case. For both defective and perfect graphene, Fe/Gp(d), Co/Gp(d) and Ni/Gp(d) are more effective in separating CO from H2 feed gas, particularly for perfect graphene. Orbital analysis suggested that the dyz and/or dxz orbitals of metal atoms play a major role in CO and H2 adsorption.

QM/MD simulations on the role of SiO2 in polymeric insulation materials

Quantum chemical molecular dynamics (QM/MD) simulations based on a self-consistent charge density functional tight-binding (SCC-DFTB) method on SiO2 filler in polyethylene (PE) showed that: in the absence of SiO2, the PE was quickly charged by high-energy electrons, which resulted in C–C or C–H bonds breaking; on the contrary, in the presence of SiO2 nanoclusters, electron trapping and accumulating were dominated by SiO2 nanoclusters rather than polyethylene, which made polyethylene be preferentially protected and increased the initial time of electrical treeing. In our calculations, we also observed double electric layers around the SiO2 nanocluster, in agreement with recent suggestions from experimental observations. Furthermore, compared with some other investigated nanoclusters, SiO2 was regarded as the most promising candidate attributed to the highest electron affinity. We further observed that once the high-energy electrons were supersaturated in the nanoclusters, the polyethylene chains would be unavoidably charged and C–H bond breaking would occur, which resulted from the interaction between H and O or Si in the nanoclusters. Following that, decomposing and cross-linking of the polyethylene chains were involved in the initial growth of electrical treeing. The current observation can potentially be used in power cable insulation.

Theoretical Investigation on the Reaction Pathways of the Oxygen Reduction Reaction on Graphene Codoped with Manganese and Phosphorus as a Potential Nonprecious Metal Catalyst

Nonprecious‐metal‐doped graphene catalysts have been proposed recently as promising candidates to substitute Pt catalysts for the oxygen reduction reaction (ORR) in fuel cells. We codoped Mn and P in divacancy graphene (MnPx, x=1–4) and we studied the stability and the catalytic activity for the ORR. The calculated formation energy indicates that MnP2‐doped divacancy graphene is energetically the most stable. The MnP2 moiety and its adjacent six C atoms are catalytically active sites for the ORR. The kinetically most favorable pathway is the hydrogenation of OOH to form O+H2O, which is a four‐electron process. The rate‐determining step is the second H2O formation, which has an energy barrier of 0.91 eV. The free energy diagrams show that for OOH hydrogenation into O+H2O all of the elementary steps are downhill at potentials of 0.0–0.67 V except for the second H2O formation.