There are a number of answers to this question depending on your comfort level with risk and how the amount of bitcoins you have to work with.
What are passive ways of earning bitcoins?
1. Join Binance. Join Binance HERE, trade for minimum 100$ and join referral program.The commission you receive from the referral program will initially be set at a rate of 20%. For accounts holding 500BNB or more, this rate will increase to 40%. If you don't have BNB in your portfolio then you'll get 20%. For example: you referred a friend and he bought BTC for 1000$. You will get 100$ in BTC! Some people are getting more than 2000 BTC (!!) from Binance Referral program!
2. Electroneum mining (read more on my blog)
3. Faucets. I don’t know anything about faucets so I cannot comment on their ability to actually produce results. I will leave that to others to comment on.
4. Lending bitcoin. This is perhaps the most interesting option. You can use a peer to peer lending site. Bitbond, BTCJam. The problem with these CAN be 2 fold. Default and volatility risk. Now I met one of Bitbond’s founders in Berlin this summer and he has said they are working on applying an approval rating to borrowers. Obviously that will mean high risk borrowers will yield a greater return. The other is volatility risk. So the value of the loan is skewed against you with a bit price movement while the loan is in play.
You can also loan BTC to Bitcoin Exchanges where they allow margin trading. Bitfinex and BitMEX both allow margin trading. The return fluctuates based on volatility, supply and demand. I would suggest short term loans of a week so you can manage the return and optimize the rate you lend at. The problem here is counterparty risk. Bitfinex has had some problems including a major hack even though it is considered a big exchange. BitMEX has not been hacked to my knowledge but they are not particularly transparent. Not suspect to my knowledge but I’m a bit risk averse where they are concerned.