The effect on the electrocatalytic oxygen evolution reaction (OER) of cobalt incorporation into the metal oxide sheets of the layered manganese oxide birnessite was investigated. Birnessite and cobalt-doped birnessite were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and conductivity measurements. A cobalt:manganese ratio of 1:2 resulted in the most active catalyst for the OER. In particular, the overpotential (η) for the OER was 420 mV, significantly lower than the η = 780 mV associated with birnessite in the absence of Co. Furthermore, the Tafel slope for Co/birnessite was 81 mV/dec, in comparison to a Tafel slope of greater than 200 mV/dec for birnessite. For chemical water oxidation catalysis, an 8-fold turnover number (TON) was achieved (h = 70 mmol of O₂/mol of metal). Density functional theory (DFT) calculations predict that cobalt modification of birnessite resulted in a raising of the valence band edge and occupation of that edge by holes with enhanced mobility during catalysis. Inclusion of extra cobalt beyond the ideal 1:2 ratio was detrimental to catalysis due to disruption of the layered structure of the birnessite phase.

中文翻译：

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钴在层状氧化锰片中的系统掺杂显着增强了水氧化催化作用

研究了将钴掺入层状氧化锰水钠锰矿的金属氧化物片中对电催化放氧反应（OER）的影响。通过X射线衍射（XRD），X射线光电子能谱（XPS），拉曼光谱和电导率测量来表征水钠锰矿和钴掺杂的水钠锰矿。钴：锰的比例为1：2导致OER的活性最高。特别是，OER的过电势（η）为420 mV，明显低于在不存在Co的情况下与水钠锰矿相关的η= 780 mV。此外，与水钠锰矿的Tafel斜率大于200 mV / dec。对于化学水氧化催化，达到了8倍的周转数（TON）（h＝ 70mmol的O ₂ / mol金属。密度泛函理论（DFT）计算预测，水钠锰矿的钴改性会导致价带边缘的增加以及该边缘被催化过程中迁移率提高的孔所占据。由于水钠锰矿相的层状结构的破坏，超出理想的1∶2比例加入额外的钴不利于催化。