Leveraging Metal Nodes in Metal–Organic Frameworks for Advanced Anodic Hydrazine Oxidation Assisted Seawater Splitting

Abstract

Metal−organic frameworks (MOFs) show great promise for electrocatalysis owing to their tunable ligand structures. However, the poor stability of MOFs impedes their practical applications. Unlike the general pathway for engineering ligands, we report herein an innovative strategy for leveraging metal nodes to improve both the catalytic activity and the stability. Our electrolysis cell with a NiRh-MOF||NiRh-MOF configuration exhibited 10 mA cm −2 at an ultralow cell voltage of 0.06 V in alkaline seawater (with 0.3 M N 2 H 4 ), outperforming its counterpart benchmark Pt/C||Pt/C cell (0.12 V). Impressively, the incorporation of Rh into a MOF secured a robust stability of over 60 h even when working in the seawater electrolyte. Experimental results and theoretical calculations revealed that Rh atoms serve as the active sites for hydrogen evolution while Ni nodes are responsible for the hydrazine oxidation during the hydrazine oxidation assisted seawater splitting. This work provides a paradigm for green hydrogen generation from seawater.

Manipulation of Electron Spins with Oxygen Vacancy on Amorphous/Crystalline Composite-Type Catalyst

“…The Brunauer–Emmett–Teller (BET) surface area and pore structures of the as-prepared samples were evaluated by recording the N 2 adsorption/desorption isotherm curves. As expected, the a-RuO 2 /NiO electrocatalyst presented a higher specific surface area (i.e., 99.22 m 2 g –1 ) compared to that of the NiO (i.e., 80.35 m 2 g –1 ) (Figure S4a), suggesting that the introduction of amorphous RuO 2 allows more active sites to be exposed and exhibits superior mass transport capabilities at the interface between catalyst and electrolyte . The Barrett–Joyner–Halenda (BJH) pore size distribution curves showed that the pore structure of the as-prepared catalyst is mesoporous with an average pore width of 3.80 nm (Figure S4b).…”

“…Since the Ni K-edge k 2 χ­( k ) oscillation curve of NiO and a-RuO 2 /NiO displayed similar oscillating frequency and shape compared to that of the NiO reference over the whole k range, an analog site occupancy for the planar Ni nodes in both NiO and a-RuO 2 /NiO is suggested (Figure S13). In addition, from the Ru K-edge EXAFS spectra and the wavelet transform (WT)-EXAFS (Figure S12b,c), two low-intensity features of a-RuO 2 /NiO are observed at ∼1.48 and 2.46 Å, possibly corresponding to the Ru–O and Ru–Ru coordination. This could be due to the combinatory effect of the amorphous structure, atomically thin thickness, and partial oxidation state. ,, …”

“…As expected, the a-RuO 2 /NiO electrocatalyst presented a higher specific surface area (i.e., 99.22 m 2 g −1 ) compared to that of the NiO (i.e., 80.35 m 2 g −1 ) (Figure S4a), suggesting that the introduction of amorphous RuO 2 allows more active sites to be exposed and exhibits superior mass transport capabilities at the interface between catalyst and electrolyte. 36 The Barrett−Joyner− Halenda (BJH) pore size distribution curves showed that the pore structure of the as-prepared catalyst is mesoporous with an average pore width of 3.80 nm (Figure S4b). These results signify that the formation of mesopores in the nanosheets is promoted during etching and pyrolysis, which led to the enlarged surface area and provide more accessible channels.…”

Hydrazine Oxidation Electrocatalysis

“…This activity is enabled by a strong interaction of the Ni z+ ions ( z = 0–2) with the defected MXene support. Atomic Ni sites could be dispersed also in a metal–organic framework, contributing to HzOR electrocatalysis in alkaline seawater alongside Rh centers in the MOF and, possibly, the Ni support . Atomically dispersed PGM-based SACs of Rh, Pd, Pt, Ir, and Ru were prepared on a nanoporous Co 2 P support, with nanoporous Co 2 P acting as a support, and Ru/Co 2 P showed the earliest E onset of −0.04 V vs RHE (Figure c) .…”

Halogen-Modified Iron-Based Metal–Organic Frameworks for Remarkably Improved Electrocatalytic Oxygen Evolution

“…Metal–organic frameworks (MOFs) are a crystalline material constructed by self-assembled metal ions centers and organic ligands . Benefiting from their customizable pore structures, high porosity, diverse chemical compositions, and unique designable morphologies, MOFs have been extensively investigated in various fields. − The frameworks can serve as superior electronic channels, the ordered porous structure facilitates the ultrafast transport of reactants, products, and electrolytes, rendering MOFs as promising catalysts for various applications. , …”