'voluntary commitment' is correct and usable in written English.
You can use it to refer to an individual's willingness to do something without being asked or compelled to do it. For example: "John demonstrated his voluntary commitment to the cause by organizing a fundraising event."
His department confirmed, according to the minutes, that the voluntary commitment would not be legally binding.
If they make a public, voluntary commitment, they'll try to follow through.
The idealistic dimension is the notion of voluntary commitment to both client interests and public values.
Just recently, there was news of a "historic voluntary commitment" by the auto industry to make S.U.V.s safer.
Meanwhile Lord Wei, Mr Cameron's Big Society adviser, has reduced his own voluntary commitment to the task.
The first Vienna Initiative "was based on voluntary commitment by banks," said Otilia Simkova, an analyst at the consulting firm Eurasia Group in London.
It was explained to him that voluntary commitment to a state institution was for 2 years, and could not easily be terminated as at a private sanitarium.
However, there are no sanctions for those producers who drag their heels, and the voluntary commitment does not cover imported foods.
"This is a historic voluntary commitment," said Eron Shosteck, a spokesman for the Alliance of Automobile Manufacturers, an industry lobbying group that oversaw the joint safety effort.
Alongside her voluntary commitment to VCC, she joined the National Children's Bureau developing one of the first complaints procedures for children in care.
More than 6,000 European cities have signed up to the Covenant of Mayors, a voluntary commitment to go faster and further than EU climate targets.
