You have to view the info of the card/relic in the game to unlock it in the album.
For the web version, we still don't have any plan on what to do with the excess Diamonds. The Android version has more heroes and game modes to spend your Diamonds on.
We are slow with the updates at the moment. There are some issues from upgrading the game engine. We also have some other projects in development. But, we've prepared a lot of new content for this game.