Analytical Chemistry and Center for Electrochemical Sciences (CES), Ruhr-Universität Bochum, NC04/788, 44780 Bochum (Germany) http://www.rub.de/elan.
Laboratory of Industrial Chemistry, Ruhr-University Bochum, NBCF 04/690, 44780 Bochum (Germany).
Angew Chem Int Ed Engl. 2015 Aug 24;54(35):10102-20. doi: 10.1002/anie.201500569. Epub 2015 Jul 1.
The notion of metal-free catalysts is used to refer to carbon materials modified with nonmetallic elements. However, some claimed metal-free catalysts are prepared using metal-containing precursors. It is highly contested that metal residues in nitrogen-doped carbon (NC) catalysts play a crucial role in the oxygen reduction reaction (ORR). In an attempt to reconcile divergent views, a definition for truly metal-free catalysts is proposed and the differences between NC and M-Nx /C catalysts are discussed. Metal impurities at levels usually undetectable by techniques such as XPS, XRD, and EDX significantly promote the ORR. Poisoning tests to mask the metal ions reveal the involvement of metal residues as active sites or as modifiers of the electronic structure of the active sites in NC. The unique merits of both M-Nx /C and NC catalysts are discussed to inspire the development of more advanced nonprecious-metal catalysts for the ORR.
无金属催化剂是指经过非金属元素修饰的碳材料。然而，一些所谓的无金属催化剂是使用含金属前体制备的。有争议的是，氮掺杂碳（NC）催化剂中的金属残留物在氧还原反应（ORR）中起着关键作用。为了调和不同的观点，提出了真正无金属催化剂的定义，并讨论了 NC 和 M-Nx /C 催化剂之间的差异。XPS、XRD 和 EDX 等技术通常无法检测到的金属杂质水平显著促进了 ORR。掩蔽金属离子的中毒测试表明，金属残留物作为活性位点或作为 NC 中活性位点电子结构的调节剂参与其中。讨论了 M-Nx /C 和 NC 催化剂的独特优点，以激发开发更先进的非贵金属 ORR 催化剂。
