Mounting a hydrogenase analog on calixarenes—designing a nature-inspired solid state catalyst for fuel cells by density functional theory

The hydrogen-fuel PEFC (polymer electrolyte fuel cell) is among the most promising alternative power generators of the future. But for it to become widely used, an alternative catalyst to platinum must be developed. While there have been previous attempts to synthesize hydrogenase mimics for this purpose, the current state of artificial hydrogenases can be summarized into two groups: sufficiently active but not in a stable solid state; and in the solid state but not sufficiently active. We model a modified active site of Fe-only hydrogenases deposited on a variety of calixarenes for solid-state support by density functional calculations. Among the calixarenes considered, our calculations have shown that calix[5]arene is so far the most viable macrocycle to hold the di-iron site. Our calculations also show that the crucial hydrogenase active site characteristics are maintained in this material: having an Fe--Fe bond and anti-bond at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) respectively; and the bonding orbitals on the Fe centers connected to the sulfur of the electron chain at the HOMO.