He intends to take on that responsibility in place of his friend.
Literal
Friend [in place of-に変わり] he [topic-は] that responsibility [object-を] take-on [intention-つもりだ].
に変わり ('in place of, on behalf of') marks the friend as the one being substituted for. 引き受ける ('to take on, undertake') is the standard verb for accepting responsibility. つもりだ declares firm intention.