(495e) Electric Fields Accelerated Nitrogen Chemistry

Inventing a scalable, energy-efficient, low-temperature and -pressure catalytic technology that utilizes renewable energy is essential for sustainable ammonia synthesis. A current grand challenge is to use renewable energy to activate N₂ under mild conditions (i.e., 500 K and 1 atm), but innovative, renewable technologies must first overcome two drawbacks: (1) The current Haber-Bosch process is too large to be deployable for a renewable energy generator. (2) At low temperature, the reaction rates of ammonia synthesis are kinetically restricted due to the high activation barrier of initial N₂ dissociation step. At low pressure, the N₂ conversion of ammonia synthesis is thermodynamically limited.¹

To tackle the above challenges, we designed modular, sustainable ammonia synthesis driven by renewable electric fields.² DFT calculations³ show that high electric fields can shift the net reaction thermodynamics equilibrium (Figure 1(a)). The high positive electric fields can also alter ammonia synthesis mechanism without passing the kinetically unfavorable N₂ dissociation (Figure 1(b)). Under no electric fields, the most favorable thermodynamic reaction pathway of ammonia synthesis is via N₂ dissociation. While under a high positive electric field, the most favorable thermodynamic reaction pathway is via hydrogenation of N₂* to form N₂H*(Figure 1(c)). In addition, the positive field further lowers the energetics of most favorable reaction path.

The fundamental science of enhanced reaction rates, improved selectivity, altered reaction mechanism of catalysis via high electric field can advance the fields of catalysis under reactors, in which a large external electric field exists, such as STM probe ''nanoreactors'', in probe-bed-probe reactors, and in capacitor reactors. The fundamental science here can also expand our scope of vision on the confinement–internal field effects on zeolite catalysis.

References

1. Honkala, K., et al., Science, 307, 555-558, 2005.

1. Che, F., et al., ACS Catalysis, 8, 5153-5174, 2018.
2. Che, F, in preparation, 2021.