This review summarizes and discusses the recent efforts devoted to the material design and reactor engineering for electrocatalytic nitrogen reduction to ammonia under ambient conditions.

In order to understand the initiation and propagation of three-dimensional (3D) embedded parallel cracks in brittle rock under uniaxial and biaxial compression, a preparation method of a transparent rock-like material was proposed in order to observe the propagation process of cracks in brittle rock. Uniaxial and biaxial compression tests were carried out on the transparent rock-like samples containing two embedded 3D parallel cracks. Four types of crack propagation modes were observed: wing crack, petaloid crack, flat-wing crack, and ring-like crack. It is also found that the direction of lateral pressure relative to the strike of the embedded crack has a significant effect on the propagation direction of new generated cracks: a lateral pressure parallel to the strike of the embedded cracks promotes crack propagation in the direction of the maximum principal stress; on the other hand, a lateral pressure normal to the strike of the embedded cracks promotes cracks propagation around the embedded crack at an angle of 30°–60°, forming ring-like cracks, which is similar to the zonal disintegration phenomenon monitored around deep underground excavations.

To investigate the dynamic compressive properties and the law of energy dissipation of freeze–thaw-damaged sandstone, static and dynamic compressive experiments were conducted. The influences of the number of freeze–thaw cycles and strain rate on strength characteristics, energy dissipation rate and the fractal dimension characteristics of sandstone were evaluated. Based on the peak energy dissipation rate, a freeze–thaw damage variable was established. The results show that peak strength increases exponentially with strain rate, and there exists a strain rate threshold. When strain rate is below this threshold, the increasing rate of the DIF slows down with the increase in the number of freeze–thaw cycles; when strain rate is higher than this threshold, the increasing rate of the DIF increases with the increase in the number of freeze–thaw cycles. In addition, the fractal dimension increases with the number of freeze–thaw cycles as well as the strain rate. Based on the freeze–thaw damage variable established, the damage degree of sandstone under freeze–thaw cycling can be characterized.