We have prepared Bitcoin addresses without keys.
And there is the issue with such burn addresses. How do you prove you do not know the keys to these addresses? You can pick an address such as the ones given above where it is incredibly unlikely you have managed to find a private key which gives such an address, but you cannot prove that you 100% do not know the keys.We wanted an irrefutable method of removing Bitcoin from circulation. So here we are. Once again thank you for the recommendation.
So the next question is, what exactly are you planning that requires bitcoin to be provably burnt? Most of the time people want to set up such an address it is to distribute an altcoin or a reward of some sort to people who have sent bitcoin to that address. The problem with using OP_RETURN for this kind of thing is two-fold. Firstly, it is far more complicated to perform than simply sending bitcoin to an address, many people will struggle to do it, and most wallets don't support it. Secondly, you need a way of verifying that that particular OP_RETURN transaction was one you were interested in, but this could easily be solved by requiring the participants to include a specific string in their OP_RETURN data. 
