Substitute for refined white flour to make fried potato wedges crispy?

You could substitute any flour you like, the purpose of the coating is to give it some extra crisp when frying. I would suggest maybe rice flour or you could use whole wheat flour but the taste may be different.

IMO, I would skip that step altogether though. A potato wedge is just a french fry cut in a different shape and we don't dredge french fries.

The coating of flour serves two purposes at once. First, it carries flavor - the flour-seasoning mix sticks better to the potatoes than a seasoning-only mixture could. Second, it gives you a crisp texture, absorbing oil, without letting much oil through to the actual potato, to prevent it from getting greasy.

For both, the closer you get to pure starch, the better results you will get. You can use a refined flour or starch made from practically any tuber or grain with good results. Which one you choose is probably a matter of practicality, as not all of them are equally available everywhere.

If you want to come away from the starch, whole-grain flours will also work reasonably well. Choose finely ground ones and be aware that most of them will introduce their own taste. This can be an advantage or disadvantage, depending on whether you like the taste combination. I would refrain from the strongest tasting ones such as maize flour.

I would advise against legume or nut flours. They contain even less starch than whole grain flours, but exactly for this reason they will fail at the two roles I noted above.

If you are asking yourself why you would want to go to alternatives with less starch: most of the concerns this article has about "refined white flour" (which happens to be about 90% wheat starch) are commonly expressed for all kinds of starch (except for numbers 5 and 6 which are wheat-specific). So, if you believe the article, you should avoid everything well-suited as a replacement for the flour, and look for alternatives which deliver an acceptable result while introducing less starch into your diet. While researching this, don't forget that the potatoes will deliver the largest starch amount in this recipe anyway, so if you decide to reduce starch consumption, you should probably remove this from the menu altogether.

I find whole oat flour provides an excellent crispyness to fried veggies. I mill my own from steel cut groats, but you can probably either buy the stuff, or make it in small quantities from groats or oatmeal with a spinning blade type spice grinder.