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Effect of pH on the Activity of Platinum Group Metal-Free Catalysts in Oxygen Reduction Reaction
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-03-01 00:00:00 , DOI: 10.1021/acscatal.7b03991 Santiago Rojas-Carbonell 1 , Kateryna Artyushkova 1 , Alexey Serov 1 , Carlo Santoro 1 , Ivana Matanovic 1 , Plamen Atanassov 1
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-03-01 00:00:00 , DOI: 10.1021/acscatal.7b03991 Santiago Rojas-Carbonell 1 , Kateryna Artyushkova 1 , Alexey Serov 1 , Carlo Santoro 1 , Ivana Matanovic 1 , Plamen Atanassov 1
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The impact of the electrolyte’s pH on the catalytic activity of platinum group metal-free (PGM-free) catalysts toward the oxygen reduction reaction (ORR) was studied. The results indicate that the ORR mechanism is determined by the affinity of protons and hydroxyls toward multiple functional groups present on the surface of the PGM-free catalyst. It was shown that the ORR is limited by the proton-coupled electron transfer at pH values below 10.5. At higher pH values (>10.5), the reaction occurs in the outer Helmholtz plane (OHP), favoring hydrogen peroxide production. Using a novel approach, the changes in the surface chemistry of PGM-free catalyst in a full pH range were studied by X-ray photoelectron spectroscopy (XPS). The variations in the surface concentration of nitrogen and carbon species are correlated with the electron transfer process and overall kinetics. This study establishes the critical role of the multitude of surface functional groups, presented as moieties or defects in the carbonaceous “backbone” of the catalyst, in mechanism of oxygen reduction reaction. Understanding the pH-dependent mechanism of ORR provides the basis for rational design of PGM-free catalysts for operation across pH ranges or at a specific pH of interest. This investigation also provides the guidelines for developing and selecting ionomers used as “locally-confined electrolytes”, by taking into account affinities and possible interactions of specific functional groups of the PGM-free catalysts with protons or hydroxyls facilitating the overall ORR kinetics.
中文翻译：
pH值对铂族金属无催化剂氧还原反应活性的影响
研究了电解质的pH值对无铂族金属（无PGM）催化剂对氧还原反应（ORR）的催化活性的影响。结果表明，ORR机制是由质子和羟基对无PGM催化剂表面上存在的多个官能团的亲和力决定的。结果表明，在pH值低于10.5时，ORR受质子耦合电子传递的限制。在较高的pH值（> 10.5）下，反应发生在外部亥姆霍兹平面（OHP）中，有利于过氧化氢的产生。使用新颖的方法，通过X射线光电子能谱（XPS）研究了在整个pH范围内无PGM催化剂的表面化学变化。氮和碳物质的表面浓度变化与电子转移过程和整体动力学相关。这项研究建立了许多表面官能团在氧还原反应机理中的关键作用，这些表面官能团表现为催化剂的碳质“主链”中的部分或缺陷。了解ORR的pH依赖性机理为合理设计不含PGM的催化剂提供了基础，该催化剂可在整个pH范围内或在特定的特定pH下运行。这项研究还通过考虑亲和力以及无PGM催化剂的特定官能团与质子或羟基的可能相互作用，为开发和选择用作“局限电解质”的离聚物提供了指导原则，从而促进了整体ORR动力学。
更新日期：2018-03-01
中文翻译：
pH值对铂族金属无催化剂氧还原反应活性的影响
研究了电解质的pH值对无铂族金属（无PGM）催化剂对氧还原反应（ORR）的催化活性的影响。结果表明，ORR机制是由质子和羟基对无PGM催化剂表面上存在的多个官能团的亲和力决定的。结果表明，在pH值低于10.5时，ORR受质子耦合电子传递的限制。在较高的pH值（> 10.5）下，反应发生在外部亥姆霍兹平面（OHP）中，有利于过氧化氢的产生。使用新颖的方法，通过X射线光电子能谱（XPS）研究了在整个pH范围内无PGM催化剂的表面化学变化。氮和碳物质的表面浓度变化与电子转移过程和整体动力学相关。这项研究建立了许多表面官能团在氧还原反应机理中的关键作用，这些表面官能团表现为催化剂的碳质“主链”中的部分或缺陷。了解ORR的pH依赖性机理为合理设计不含PGM的催化剂提供了基础，该催化剂可在整个pH范围内或在特定的特定pH下运行。这项研究还通过考虑亲和力以及无PGM催化剂的特定官能团与质子或羟基的可能相互作用，为开发和选择用作“局限电解质”的离聚物提供了指导原则，从而促进了整体ORR动力学。
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