Here's why:

* Direct Current (DC): The flow of electric charge is consistently in one direction. This is essential for electrolysis because it ensures that ions are consistently driven towards the electrodes with the correct polarity (positive ions to the negative electrode, negative ions to the positive electrode).

* Alternating Current (AC): The flow of electric charge changes direction periodically. If AC were used, the ions would constantly be switching directions, preventing any significant electrochemical reaction.

In summary, direct current is crucial for electrolysis because it provides a consistent and unidirectional flow of charge, allowing for the controlled movement of ions and the desired chemical reactions to occur.