No abstract

Highly efficient catalysts with enough selectivity and stability are essential for electrochemical nitrogen reduction reaction (e-NRR) that has been considered as a green and sustainable route for synthesis of NH 3 . In this work, a series of three-dimensional (3D) porous iron foam (abbreviated as IF) selfsupported FeS 2 −MoS 2 bimetallic hybrid materials, denoted as FeS 2 −MoS 2 @IF x , x = 100, 200, 300, and 400, were designed and synthesized and then directly used as the electrode for the NRR. Interestingly, the IF serving as a slow-releasing iron source together with polyoxomolybdates (NH 4 ) 6 Mo 7 O 24 •4H 2 O as a Mo source were sulfurized in the presence of thiourea to form self-supported FeS 2 −MoS 2 on IF (abbreviated as FeS 2 −MoS 2 @IF 200 ) as an efficient electrocatalyst. Further material characterizations of FeS 2 −MoS 2 @IF 200 show that flower cluster-like FeS 2 −MoS 2 grows on the 3D skeleton of IF, consisting of interconnected and staggered nanosheets with mesoporous structures. The unique 3D porous structure of FeS 2 −MoS 2 @IF together with synergy and interface interactions of bimetallic sulfides would make FeS 2 −MoS 2 @IF possess favorable electron transfer tunnels and expose abundant intrinsic active sites in the e-NRR. It is confirmed that synthesized FeS 2 −MoS 2 @IF 200 shows a remarkable NH 3 production rate of 7.1 ×10 −10 mol s −1 cm −2 at −0.5 V versus the reversible hydrogen electrode (vs RHE) and an optimal faradaic efficiency of 4.6% at −0.3 V (vs RHE) with outstanding electrochemical and structural stability.

chem.8b03248. Tables of selected bond lengths and angles for compounds 1−9, structural figures of 1−9, the PXRD patterns, the XPS data, the IR spectra, the TGA curves of 1−9, and the figures of electrocatalytic activity, amperometric sensors and the fluorescence (PDF)

Precise design and construction of catalysts with satisfied performance for ambient electrolytic nitrogen reduction reaction (e-NRR) is extremely challenging. By in situ integrating an electron-rich polyoxometalates (POMs) into stable metal organic frameworks (MOFs), five POMs-based MOFs formulated as [Fe x Co y (Pbpy) 9 (ox) 6 (H 2 O) 6 ][P 2 W 18 O 62 ]•3H 2 O (abbreviated as Fe x Co y MOF-P 2 W 18 ) are created and directly used as catalysts for e-NRR. Their electrocatalytic performances are remarkably improved thanks to complementary advantages and promising possibilities of MOFs and POMs. In particular, NH 3 yield rates of 47.04 µg h −1 mg cat. −1 and Faradaic efficiency of 31.56% by FeCoMOF-P 2 W 18 for e-NRR are significantly enhanced by a factor of 4 and 3, respectively, compared to the [Fe 0.5 Co 0.5 (Pbpy)(ox)] 2 •(Pbpy) 0.5 . The cyclic voltammetry curves, density functional theory calculations and in situ Fouriertransform infrared spectroscopy confirm that there is a directional electron channel from P 2 W 18 to the MOFs unit to accelerate the transfer of electrons. And the introduction of bimetals Fe and Co in the P 2 W 18 -based MOFs can reduce the energy of the *N 2 to *N 2 H step, thereby increasing the production of NH 3 . More importantly, this POM in situ embedding strategy can be extended to create other e-NRR catalysts with enhanced performances, which opens a new avenue for future NH 3 production for breakthrough in the bottleneck of e-NRR.

The development of POM‐based coordination polymers (CPs) provides a promising chance to approach excellent bifunctional electrode materials. Herein, three new polyoxometalates (POMs)‐based three‐dimensional (3D) inorganic‐organic hybrid compounds, [HPMVI9MV3O40]CuI5[4‐atrz]6⋅XH2O [M=Mo(1) or W(2), X=1(1)], [H2SiMoVI9MoV3O40]CuI5[4‐atrz]6⋅H2O (3) have been synthesized via hydrothermal reaction and explored as pseudocapacitive and sensors electrode materials. These compounds possess a novel three‐dimensional sandwich structure formed from POMs and ring CuI‐4‐atrz complexes by using Cu1 as nodes. As capacitor electrode materials, compounds 1 and 3 with Mo‐containing POMs show much higher specific capacitance than 2, which is because that POMs with Mo as metal atoms have much higher oxidation capacity than those with W. When these compounds are used as sensors to detect NO2− and Cr2O72−, compound 3 shows the highest sensitivity, lowest detection limit and most excellent anti‐interference ability. These results indicate that combining POMs and CuI‐4‐atrz complexes to form POM‐based coordination polymers with unique microstructures greatly improve the electrochemical performance and stability of traditional POMs as electrode materials, which are attributed to excellent redox properties of POMs, and unique three‐dimensional structure formed due to introduction of Cu‐4‐atrz complex. This work provides a promising direction for exploring novel bifunctional electrode materials.