Figure 5 Calculation of density function theory. (a) Proposed 4e- mechanism of OER on NiFeCoCN (110) in acidic media. The Fe coordinated Oh site is the active site. Ni, Fe, Co, C, N, O and H atoms are marked in silver, yellow, blue, brown, white, red and pink colors, respectively. (b) Gibbs free-energy diagrams of NiFeCo and NiFeCoCN. (c) Projected density of states of Fe total, Fe s, Fe p and Fe d orbitals in NiFeCo and NiFeCoCN. (d) The charge transfer before and after C/N replacement O is described by the electron transfer difference calculated based on the Bader charge computations. The black arrow shows the direction of electron transfer.
CONCLUSION
In summary, a nonprecious nanoporous NiFeCoCN MEA electrode was successfully fabricated by a facile method of high-temperature sintering with urea as a C/N source and pore-forming agent. The NiFeCoCN MEA electrode for the OER in 0.5 M H2SO4 has a lower Tafel slope (52.4 mV dec-1) than noble IrO2/Ti (58.6 mV dec-1) and an overpotential of 432 mV at 10 mA cm-2. The NiFeCoCN MEA electrode can be continuously operated for 28 hours at a current density of 100 mA cm-2 in 0.5 M H2SO4, which confirms the superior stability for the acidic OER. In addition, NiFeCoCN MEA has an overpotential of 177 mV at a current density of 10 mA cm-2 and a Tafel slope of 36.1 mV dec-1, which are also lower than those of the IrO2/Ni foam electrode (215 mV and 68.8 mV dec-1, respectively). This work provides a novel strategy to design and fabricate OER electrocatalysts with low price and high performance in pH-universal media.