There is no substitute for baking powder, and baking powder cannot be replaced with anything else.

While baking powder has baking soda as an ingredient, it is acidic powder (such as cream of tartar) added after precision testing to balance its pH, so basically, while baking soda is a base-carrying substance, commercially available baking powder is a neutral powder, and therefore baking soda and baking powder can't be replaced arbitrarily.

Expanded Information:

Baking powder it is a white powder made of baking soda in combination with other acidic materials and cornstarch as a filler. When the baking powder comes into contact with water, the acidic and alkaline powders dissolve in the water and react, and some of them start to release carbon dioxide (CO?)

At the same time, during the baking and heating process, more gases are released, and these gases make the product to achieve the effect of expansion and fluffiness.

Baking powder is a complex bulking agent, also known as baking powder and baking soda, mainly used as a rapid loosening agent for pasta-based foods. There are some sweet and edible baking powder, which is a kind of fast leavening agent, mainly used for the fast leavening of grain products. It is used in the production of cakes, cakes, buns, steamed bread, shortbread, bread and other foods.

Baidu Encyclopedia - Baking Powder