Under Section 2 (v) of the Dissolution of Muslim Marriage Act, 1939 you can get divorce on the ground of his impotency by filing petition in Family Court, where you reside. You can approach the District Legal Services Authority in District Court and you will get a free legal aid advocate to help you. Everything will be provided free of cost. It will take two to three years to get divorce from family court. In the court a direction will be given to husband to appear before a medical board of the government hospital and get potency certificate. If he fails to get such certificate or fails to appear before such board, adverse inference can be drawn and you would get divorce.
In Sharia law also, you can go for Khulla and get divorce, as muslim marriage is a contractual marriage and it can be resciended at the will of any one of the parties. Contact Maulvi of your area Masjid and he will issue notice to your husband and after that marriage will be annuled. Best of luck.