Geobacter sulfur reducens biofilms were formed under constant polarisation at −0.6 V vs. Ag/AgCl on stainless steel cathodes to catalyse the reduction of fumarate. The time-evolution of the current strongly depended on the quality of the inoculum. Inoculating with young cells significantly shortened the initial lag-phase and using the same inoculum improved the reproducibility of the current–time curves. The whole set of experiments showed that 254SMO stainless steel provided higher current densities (on average 14.1 A/m2) than biofilms formed on 316L stainless steel (on average 4.5 A/m2). Biofilm coverage assessed by epifluorescent microscopy showed that coverage ratios were generally higher for 316L than for 254SMO. It must be concluded that 254SMO is more efficient in transferring electrons to bacterial cells than 316L. Mott–Schottky diagrams recorded on both materials under conditions of electrolysis in the absence of microorganisms showed that the surface oxide layers had similar n-type semi-conductive behaviour for potential values higher than the flat band potential. In contrast, 316L exhibited slight p-type behaviour at potential lower than the flat band potential, while 254SMO did not. The higher electrochemical performances of biocathodes formed on 254SMO are explained by semi-conductive properties of its passive layer, which prevented the p-type behaviour occurring in cathodic electrolysis conditions.
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机译：在-0.6 V相对于Ag / AgCl的恒定极化下，在不锈钢阴极上形成了Geobacter硫还原剂生物膜，以催化富马酸盐的还原。电流的时间演变很大程度上取决于接种物的质量。用年轻细胞接种可大大缩短初始滞后阶段，并且使用相同的接种物可提高电流-时间曲线的可重复性。整套实验表明，与316L不锈钢上形成的生物膜（平均4.5 A / m2）相比，254SMO不锈钢提供更高的电流密度（平均14.1 A / m2）。通过落射荧光显微镜评估的生物膜覆盖率表明，316L的覆盖率通常比254SMO高。必须得出的结论是，254SMO比316L更有效地将电子转移到细菌细胞中。在没有微生物的情况下在电解条件下在两种材料上记录的莫特-肖特基图表明，对于高于平带电势的电势值，表面氧化物层具有相似的n型半导体行为。相反，316L在比平带电势低的电势下表现出轻微的p型行为，而254SMO没有。 254SMO上形成的生物阴极具有更高的电化学性能，可通过其钝化层的半导电特性来解释，这可以防止在阴极电解条件下发生p型行为。
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