2 research outputs found
Intermetallic Alloys as CO Electroreduction Catalystsî—¸Role of Isolated Active Sites
One of the main challenges associated
with the electrochemical
CO or CO<sub>2</sub> reduction is poor selectivity toward energetically
rich products. In order to promote selectivity toward hydrocarbons
and alcohols, most notably, the hydrogen evolution reaction (HER)
should be suppressed. To achieve this goal, we studied intermetallic
compounds consisting of transition metal (TM) elements that can reduce
CO (Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu) separated by TM and post transition
metal elements (Ag, Au, Cd, Zn, Hg, In, Sn, Pb, Sb, and Bi) that are
very poor HER catalysts. In total, 34 different stable binary bulk
alloys forming from these elements have been investigated using density
functional theory calculations. The electronic and geometric properties
of the catalyst surface can be tuned by varying the size of the active
centers and the elements forming them. We have identified six different
potentially selective intermetallic surfaces on which CO can be reduced
to methanol at potentials comparable to or even slightly positive
than those for CO/CO<sub>2</sub> reduction to methane on Cu. Common
features shared by most of the selective alloys are single TM sites.
The role of single sites is to block parasitic HER and thereby promote
CO reduction
Electrochemical CO<sub>2</sub> and CO Reduction on Metal-Functionalized Porphyrin-like Graphene
Porphyrin-like metal-functionalized
graphene structures have been
investigated as possible catalysts for CO<sub>2</sub> and CO reduction
to methane or methanol. The late transition metals (Cu, Ag, Au, Ni,
Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) and some p (B, Al, Ga) and s (Mg)
metals comprised the center of the porphyrin ring. A clear difference
in catalytic properties compared to extended metal surfaces was observed
owing to a different electronic nature of the active site. The preference
to bind hydrogen, however, becomes a major obstacle in the reaction
path. A possible solution to this problem is to reduce CO instead
of CO<sub>2</sub>. Volcano plots were constructed on the basis of
scaling relations of reaction intermediates, and from these plots
the reaction steps with the highest overpotentials were deduced. The
Rh–porphyrin-like functionalized graphene was identified as
the most active catalyst for producing methanol from CO, featuring
an overpotential of 0.22 V. Additionally, we have also examined the
hydrogen evolution and oxidation reaction, and in their case, too,
Rh–porphyrin turned out to be the best catalyst with an overpotential
of 0.15 V