A chemical active medium on the base of Belousov-Zhabotinsky (BZ) medium was used to design a "chemical diode". This system, similar to a semiconductor diode, shows unidirectional propagation of chemical pulses and may be possible to be used to construct a massively parallel computational medium. The system of two mesoporous glass plates with ferroin loaded at the surface was covered by BZ solution and maintained propagating excitation waves. The unidirectional propagation was observed when the plates were placed so that the corner of the one plate was close to the plane side of the other plate. The study shows that the important feature of the system is the geometrical arrangement of the plates and the gap distance between them. Computer simulations confirm the experimental results.