Functional Modification of Dawson‐Type Arsenomolybdate for Enhanced Ultracapacitor Performance and Nitrate‐to‐Ammonia Production

Abstract Polyoxometalates (POMs) are promising electrocatalysts and pseudo‐capacitive materials due to their reversible multi‐electron redox properties. In this study, Dawson‐type mono‐arsenic‐capped arsenomolybdate are anchored into channels of {Cu(trz) 2 } 7 metal–organic network yielding a solution‐stable host‐guest structure, [{Cu I (trz) 2 } 7 {As III As V 2 Mo V 4 Mo VI 14 O 62 }] 2 ·3H 2 O ( 2 ), which exhibits higher conductivity and specific capacity, excellent rate performance and cycle stability than (biz) 9 (Hbiz) 3 {As III 1.5 As V 2 Mo 18 O 62 } 2 ·2H 2 O ( 1 ) and most reported POMs, ascribing to the excellent Faraday properties of POMs, metal–organic conductive network, and the advantages of host‐guest structure in surface area and stability. The AC// 2 ‐CPE device demonstrates energy density and power density of 25.45 Wh kg −1 and 1991.53 W kg −1 , and 92.4% capacity retention after 10 000 cycles. Moreover, compound 2 as nitrate reduction reaction (NO₃RR) electrocatalyst achieves a current density of 150 mA cm −2 at −0.5 V, ammonia production rate of 15.28 mg h −1 cm −2 , and Faradaic efficiency of up to 90%. Density functional theory is employed to thoroughly investigate the adsorption active sites and the detailed energetic steps corresponding to the overall reaction pathway of NO 3 RR regulated by compound 2 . This study reveals that encapsulating POMs clusters into a metal–organic network can increase the redox active sites, improve stability, and conductivity, thereby enhancing the energy storage and catalytic activity of POMs at the molecular level.