抗水淹及H2O2氧化三维多级孔道氧电极的构建与催化性能研究

The development of the non-platinum-based oxygen reduction reaction catalyst with superior activity as well as excellent stability has been the key to realize the commercialization of fuel cells. Recently, transition metal-nitrogen-doped carbon materials (M-N/C catalysts) are considered to be the most promising alternative for platinum-based catalysts. However, due to the lack of active sites on the three-phase boundary and the low volume activity, the activity of M-N/C catalysts cannot satisfy the demand of fuel cells. Moreover, as a byproduct of the oxygen reduction, H2O2 would be generated in lager amount when M-N/C catalysts were employed as the oxygen reduction catalysts. And the generated H2O2 not only causes the degradation of active sites, but also makes the surface extremely hydrophilic resulting in the catalyst layer flooding; therefore M-N/C catalysts possess the poor durability in fuel cells. On the basis of the above understandings, herein, we proposed using metal oxides with the catalysis on the decomposition of H2O2 as the template to synthesize M-N/C catalyst precursors featured with a hollow structure or hollow compound structure with reserved metal oxide. A three-dimensional porous catalyst with high decomposition ability of H2O2 could be obtained further by employing the “shape fixing via salt recrystallization” method and followed loading process. The as-prepared catalysts with an excellent three-dimensional porous structure are expected to engender most of the active sites to be exposed on the three-phase interface and simultaneously accelerate the mass transfer process. Most importantly, the problems, that degradation or flooding of the catalytic active sites caused by the attraction or oxidation of accumulated H2O2 in the micro-pores respectively, could be efficiently avoided by the promoter catalyst. Thus, both of activity and durability of M-N/C could be improved.

发展高活性及高稳定性的非铂基燃料电池阴极氧还原催化剂一直是燃料电池商业化的瓶颈问题。然而，目前最引人瞩目的过渡金属氮碳催化剂（M-N/C催化剂）仍然存在着活性位点暴露不充分，体积活性差等问题，不仅如此，M-N/C催化剂在使用过程中活性位极易被氧还原不彻底产物H2O2所攻击造成活性位点的失活与水淹，使得此类催化剂在燃料电池中具有较差的稳定性。本项目针对上述问题，提出利用对H2O2分解有分解作用的金属氧化物为模板，合成具有中空结构的M-N/C催化剂前躯体或者金属氧化物部分保留的中空复合结构，结合“盐溶液重结晶固形高温炭化法”及后续负载，构建负载有助催化剂的三维多孔道结构，充分地暴露活性位点，有效地加速传质过程，高效地解决由于催化氧还原不充分导致的H2O2堆积在活性位点上所造成的催化活性位破坏以及由于H2O2氧化造成M-N/C催化层亲水而导致的水淹问题，全方位的提高M-N/C的活性及稳定性。

发展高活性及高稳定性的非铂基燃料电池阴极氧还原催化剂一直是燃料电池商业化的瓶颈问题。然而，目前最引人瞩目的过渡金属氮碳催化剂（M-N/C催化剂）仍然存在着活性位点暴露不充分，体积活性差等问题，不仅如此，M-N/C催化剂在使用过程中活性位极易被氧还原不彻底产物H2O2所攻击造成活性位点的失活与水淹，使得此类催化剂在燃料电池中具有较差的稳定性。本项目针对上述问题，在传统模板法的基础上引入了具备更好形貌可控性与孔结构可控性的新型MnO2牺牲模板、可气化氧化锌/二氧化硅胶体复合模板和嵌段共聚物软模板，并利用这些新型模板完成了开口式中空多孔Fe-N/C催化剂、Co/NCNTs三维多级孔结构催化剂、氮/硫掺杂碳基空心催化剂的可控制备。除模板法外，还开展了高温相变调控碳材料表界面与孔道结构、乳液界面聚合等新型氧还原催化剂可控合成方法研究，完成了多种抗水淹及H2O2氧化的三维多级孔道氧电极的可控制备。制备了MnxOy/N-C三维多级孔道氧电极，通过构建负载有助催化剂的三维多孔道结构，充分地暴露活性位点，有效地加速传质过程，高效地解决由于催化氧还原不充分导致的H2O2堆积在活性位点上所造成的催化活性位破坏以及由于H2O2氧化造成M-N/C催化层亲水而导致的水淹问题，全方位的提高M-N/C的活性及稳定性。