Nitrogen‐Doped Porous Nickel Molybdenum Phosphide Sheets for Efficient Seawater Splitting

Abstract

Hydrogen is emerging as an alternative clean fuel; however, its dependency on freshwater will be a threat to a sustainable environment. Seawater, an unlimited source, can be an alternative, but its salt‐rich nature causes corrosion and introduces several competing reactions, hindering its use. To overcome these, a unique catalyst composed of porous sheets of nitrogen‐doped NiMo3P (N‐NiMo3P) having a sheet size of several microns is designed. The presence of large homogenous pores in the basal plane of these sheets makes them catalytically more active and ensures faster mass transfer. The introduction of N and Ni into MoP significantly tunes the electronic density of Mo, surface chemistry, and metal‐non‐metal bond lengths, optimizing surface energies, creating new active sites, and increasing electrical conductivity. The presence of metal‐nitrogen bonds and surface polyanions increases the stability and improves anti‐corrosive properties against chlorine chemistry. Ultimately, the N‐NiMo3P sheets show remarkable performance as it only requires overpotentials of 23 and 35 mV for hydrogen evolution reaction, and it catalyzes full water splitting at 1.52 and 1.55 V to achieve 10 mA cm−2 in 1 m KOH and seawater, respectively. Hence, structural and compositional control can make catalysts effective in realizing low‐cost hydrogen directly from seawater.

Seawater to Green Hydrogen: Future of Green Energy

“…In recent years, significant efforts have been made to develop active and stable electrode materials to support the direct seawater electrolysis technology to avoid undesired side reactions. Strategies like heteroatom doping, [14] surface coating, [15] alloying, [5] etc., have been used to develop catalysts for direct seawater splitting, which can tackle the corrosive chlorine chemistry and prevent electrode corrosion. In our recent work, porous ultrathin sheets of nitrogen‐doped nickel molybdenum phosphide (N‐NiMo 3 P) were synthesized with a polyanion layer on its surface consisting of phosphate and nitrate anions, which repels the negatively charged chloride anions and prevents the formation of chlorine gas, thus enhancing the performance and stability of the catalyst in seawater electrolyte [14] .…”

“…In our recent work, porous ultrathin sheets of nitrogen-doped nickel molybdenum phosphide (N-NiMo 3 P) were synthesized with a polyanion layer on its surface consisting of phosphate and nitrate anions, which repels the negatively charged chloride anions and prevents the formation of chlorine gas, thus enhancing the performance and stability of the catalyst in seawater electrolyte. [14] In another work, a Lewis acid layer was introduced over the surface of CoO x to manipulate the local reaction environment. The CoO x was coated with a layer of Cr 2 O 3, which assisted in splitting the water molecule with in-situ generation of hydroxyl anions surrounding the catalyst.…”

Multi-interfacial engineering of an interlinked Ni2P–MoP heterojunction to modulate the electronic structure for efficient overall water splitting

“…13,14 Given that it is difficult for single-component catalysts to provide multiple adsorption sites to simultaneously satisfy the adsorption equilibrium of various intermediates, coupling multiple components is proposed to facilitate the kinetics of water splitting, for example, Ni-doped MoP, N-NiMo 3 P and V-CoP 2 . [15][16][17] In particular, engineering heterojunctions by combining early transition metals (ETMs, e.g. W, Mo, V) with empty or half-lled d-orbitals and d-electron-rich late transition metals (LTMs, e.g.…”

Ni/NiO@NC as a highly efficient and durable HER electrocatalyst derived from nickel(ii) complexes: importance of polydentate amino-acid ligands

“…Due to its high energy density, clean, pollution-free, and renewable characteristics, hydrogen energy has been explored as a potential energy carrier for energy infrastructure. [1][2][3][4][5] Among the many hydrogen-production technologies, hydrogen production by electrolysis is one of the most promising. [6][7][8][9][10] Materials based on precious metals, such as Pt, have demonstrated excellent catalytic characteristics for the hydrogen evolution reaction (HER).…”

“…Introduction of the heteroatom N is also conducive to enhancing the carrier concentration in the carbon matrix, thereby improving the conductivity of the material. 4,16,24,43,44 At a current density of 10 mA cm −2 in 1 M KOH, the hydrogen evolution overpotential was 100 mV (vs. RHE), and the hydrogen evolution overpotential increases by only 4 mV after 6000 continuous cyclic voltammetry (CV) scans. Notably, the performance of the prepared composite catalyst was enhanced significantly when Ni/NiO@NC was coated on different conductive substrates.…”