Media mogul Oprah Winfrey has donated $12 million to the National Museum of African American History and Culture, a new museum planned for Washington, DC's National Mall.

The museum announced the gift on Tuesday as its largest to date, and it follows Winfrey's previous gift of $1 million.

"I am so proud of African-American history and its contributions to our nation as a whole," Winfrey said in a statement released by the museum. "By investing in this museum, I want to help ensure that we both honor and preserve our culture and history, so that the stories of who we are will live on for generations to come."

Winfrey, who is an avid collector of African American art, sits on the museum's council.

The museum's 350-seat theater for visiting performers, scholars, authors and filmmakers, called the Oprah Winfrey Theater, has been named in her honor.

More than 22,000 objects from African American history that span slavery through the civil rights area and into the 21st century will come together in the new museum. The $500 million construction project is expected to open in 2015.

The U.S. government is funding half the construction costs.

Winfrey, who is on the museum's council, is expected to donate some items from her experience as a talk show host, such as a microphone.