Line two 6-cup muffin tins (or one 12-cup tin) with paper liners.
In a large bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt.
2 cups all-purpose flour, ¾ cup cocoa powder, 1½ teaspoons baking soda, 1 teaspoon baking powder, ½ teaspoon salt
In a separate bowl, whisk the granulated sugar, brown sugar, oil, eggs, and vanilla until smooth. Gradually add the dry ingredients to the wet, stirring gently just until combined.
1 cup granulated sugar, ½ cup brown sugar, ¾ cup vegetable oil, 2 large eggs, 1 teaspoon vanilla extract
Slowly alternate adding the buttermilk and boiling water to the batter, mixing on low speed until smooth. The batter will be slightly thin. Gently stir in the chocolate chips until evenly distributed.
1 cup buttermilk, 1 cup boiling water, 1½ cups semi-sweet chocolate chips
Fill each muffin cup about ¾ full. Bake in the air fryer at 350°F (180°C) for 12-15 minutes, or until a toothpick comes out with a few moist crumbs.
Let the muffins cool in the pan for 5–10 minutes, then transfer to a wire rack to cool completely.