Phase Engineering of Fe-Polyoxometalate Sub-1 nm Assemblies for High-Efficiency Photoelectrocatalytic Nitrogen Reduction

Iron-substituted polyoxometalate (Fe-POM) clusters are promising candidates for photoelectrocatalytic nitrogen reduction due to their photosensitive and electron-buffering capabilities. However, their catalytic performances are severely hindered by the intrinsic cluster configuration and dissolution-induced detachment on the electrode. Here, using Fe-POM as "superatom" building blocks, we prepared a series of one-dimensional (1D) subnanowires and two-dimensional (2D) subnanosheets driven by different cation ligands, where clusters are connected directly with a controllable arrangement. Three kinds of Keggin-type clusters can be employed as building blocks, indicating the generality of this synthetic strategy. 1D subnanowires exhibit extraordinary catalytic activity toward the photoelectrocatalytic nitrogen reduction reaction (PEC-NRR), with a high ammonia yield of 72.0 μg h-1 mg-1, representing a 4.47-fold enhancement over the discrete clusters. Experimental and theoretical evidence demonstrate that electron delocalization among Fe-POM assemblies results in narrower band gaps and enhanced light harvesting, which also lowers the energy barrier for the rate-determining step (*NNH formation). Different from the microenvironment design of active sites, the superstructural engineering may offer a versatile paradigm for the electronic structure modulation of catalysts.