Yes, you can set any collection as default. That way all your saved articles will be directly stored in that collection.

Steps for setting any collection as default:

Mobile:

• Go to the “Collections” section.
• Click on the ( Hamburger ) icon at the top left of the screen. The entire list of collections will appear.
• Long press on a collection. Few options appear on its right.
• Click on the ( Tick ) option. 
• The collection will be marked as default.

Web:

• Click on “Collections”. The entire list of collections expands.
• Click on the ( Ellipsis ) by each collection. A menu pops up.
• Click on “Mark as Default”.
• The collection will be marked as default.