# Electrocatalytic Nanomaterials Improve Microbial Extracellular Electron Transfer: A Review
## 3 Electrocatalytic Nanomaterials for Promoting EET
### Metal Sulfides  
Transition metal sulfides (TMSs) are commonly used as highly active electrocatalysts and have also been used in the field of microbial electrocatalysis (Table 1). Back in 2010, [PERSON] et al. found, for the first time, that the FeS colloids produced by _S. loilica_ PV-4 could self-organize to from electron-conducting networks, resulting in a two orders of magnitude higher electricity production of the _S. loilica_ PV-4 cells [132]. Afterward, [PERSON] et al. further proved the promotion effect of biogenic FeS nanoparticles on the _S. loilica_ PV-4 EET through a detailed investigation of the structure and composition of the cell/nanoparticle interface [114]. Similarly, the _S. oneidensis_ MR-1 cell strain was also found to generate extracellular FeS nanowires and was used as electron conduits for long-range EET [133]. The decoration of graphene with FeS\({}_{2}\) nanoparticles was demonstrated to not only benefit the enrichment of electrochemically active _Geobacter_ species but also promote the EET process, which has given rise to a fast start-up time and an unprecedented power density [115]. Recently, [PERSON] et al. proved that the biogenic FeS that formed on _S. oneidensis_ MR-1 cell surfaces during the ferrihydrite reduction process could significantly increase the EET rate through continuously monitoring the reduction rate of ferrihydrite, and they proposed that the biogenic FeS could act as a solid electron mediator for efficient EET [116]. More significantly, [PERSON] et al. proposed a concept of a single-cell electron collector (Figure 5), which was in situ built with a FeS conductive layer on and across the individual _S. oneidensis_ MR-1 cell membrane, and the single electron collector formed intimate contact with the cellular electron transfer route [117]. As a consequence, the in situ synthesized FeS single-cell electron collector efficiently wired living cells with an abiotic electrode surface, which achieved a record-high interfacial EET efficiency and performance of microbial electrochemical systems. In addition to the above-mentioned current production, the enhancement of the FeS nanointerface on microbial EET has also been widely used to accelerate the removal of environmental pollutants, such as the reduction of toxic hexavalent chromium [118] and the dechlorination of trichloroethene [119]. In the last decade, CdS has been another high-profile semiconductor metal sulfide in the field of wiring microbial EET processes due to its excellent light absorption and high photoelectron yield, which has led to a new cutting-edge research frontier of artificial photosynthesis [134; 135]. As a pioneering work, [PERSON] et al. developed an artificial photosynthetic hybrid through the self-photosensitization of a non-photosynthetic bacterium _Moorella thermoactica_ with CdS nanoparticles, in which the biological precipitated clusters of small CdS nanoparticles (<10 nm) that were deposited on the bacterial cell surface and in the periplasm could serve as light harvesters with high quantum yields, thus sustaining the cellular metabolism of _M. thermoactica_ for the selective and continuous photosynthesis of acetate from CO\({}_{2}\) over several days of light/dark cycles [120]. Afterward, a series of artificial hybrids for artificial photosynthesis have been developed, such as CdS@_Rhodospseudomonas