具有完全共轭的环状二酮结构的醌已经在电化学中用作氧化还原介体。作为对醌衍生物的2,5-二叔丁基-1,4-苯醌(DBBQ或DB-p-BQ)是用于促进锂-氧电池(LOB)中的氧还原反应(ORR)动力学的代表性放电氧化还原介体之一。在这里,我们提出,DB-p-BQ用于电子介导的氧化还原活性可能通过调节取代醌的羰基的异构构型以改变其还原电位来促进超氧化物歧化反应(SODR)。首先,我们预期在2.75V的氧/超氧化物相对于Li/Li+和3.17V的超氧化物/过氧化物之间具有还原电位的分子通过将电子从一种超氧化物(O2-)转移到另一种超氧化物以产生二氧(O2)和过氧化物(O22-)来发挥SODR催化剂的作用。通过将异构构型从对位(DB-p-BQ)更改为邻位(DB-o-BQ),二叔丁基苯醌的第一电子转移(Q/Q-)的还原电位正向移动到SODR催化剂的电位范围。DB-o-BQ的电催化SODR促进功能使反应性超氧化物浓度保持在有害水平以下,以抑制超氧化物触发的副反应,提高LOB的循环耐久性,这不是通过para形式实现的。DB-o-BQ的第二电子转移过程(Q-/Q2-),即使没有使用同款程序来促进ORR,像对位形式的Q/Q过程一样,在电极和氧之间起介导电子的作用。邻位形式的ORR促进功能增加了LOB放电容量并降低了ORR过电位。
Quinones having a fully conjugated cyclic dione structure have been used as redox mediators in electrochemistry. 2,5-Ditert-butyl-1,4-benzoquinone (DBBQ or DB-p-BQ) as a para-quinone derivative is one of the representative discharge redox mediators for facilitating the oxygen reduction reaction (ORR) kinetics in lithium-oxygen batteries (LOBs). Herein, we presented that the redox activity of DB-p-BQ for electron mediation was possibly used for facilitating superoxide disproportionation reaction (SODR) by tuning the isomeric configuration of the carbonyl groups of the substituted quinone to change its reduction potentials. First, we expected a molecule having its reduction potential between oxygen/superoxide at 2.75 V versus Li/Li+ and superoxide/peroxide at 3.17 V to play a role of the SODR catalyst by transferring an electron from one superoxide (O2-) to another superoxide to generate dioxygen (O2) and peroxide (O22-). By changing the isomeric configuration from para (DB-p-BQ) to ortho (DB-o-BQ), the reduction potential of the first electron transfer (Q/Q-) of the ditert-butyl benzoquinone shifted positively to the potential range of the SODR catalyst. The electrocatalytic SODR-promoting functionality of DB-o-BQ kept the reactive superoxide concentration below a harmful level to suppress superoxide-triggered side reaction, improving the cycling durability of LOBs, which was not achieved by the para form. The second electron transfer process (Q-/ Q2-) of the DB-o-BQ, even if the same process of the para form was not used for facilitating ORR, played a role of mediating electrons between electrode and oxygen like the Q/Q- process of the para form. The ORR-promoting functionality of the ortho form increased the LOB discharge capacity and reduced the ORR overpotential.