Short version of fix in case these links don't work in the future:
Create a shortcut to the explorer folder on your desktop, then edit the location of the shortcut so that it says "explorer" before the path. You can also change the icon by going to the shortcut --> Change Icon option. Then, pin the shortcut to the start bar.
Do note that since this is a shortcut and not an app that you're pinning, when you click the shortcut, the window will open under the main Explorer icon.
Personally, I'm a big fan of using the official pin feature to pin folders to the Explorer app (keeps the start bar clean), but I'm guessing since you're asking specifically how to pin the icon separately, that you've considered that option. But wanted to mention it as an option just in case.