These are some of the limitations of Proof of Work-
1. Centralization
Mining has been centralized because of the huge cost of electricity and equipment for mining. Since mining is becoming more profitable and lucrative, large mining pools have begun to own a large portion of the hash power on the network. This is in contrast to the decentralization of cryptocurrency.

2. Scalability
PoW could be slow and not sufficiently scalable for various use-cases. This is due to the fact that mining complicated mathematical problems can take a long time.

3. Time delays for transactions
The time required for an additional block to be placed on a Blockchain via the Proof of Work (PoW) consensus technique is referred to as delay or latency in transaction times. In Bitcoin the block is generally mined every 10 minutes. This means that confirming the validity of a transaction takes energy and effort. The delay in processing transactions and confirmation times can result from the high rate of latency.