Zìgào fènyǒng cānjiā zhè xiàng rènwù de rén bù shǎo.
Quite a few people volunteered — 'self-offered' — to take on this task.
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Archaic on its own. In modern Chinese you almost always meet it inside the set phrase 自告奋勇 ('to volunteer'). The underlying sense is 'to announce something about oneself' — either a confession (自告其罪) or a willingness (自告奋勇).