MoNi_(4)-NiO heterojunction encapsulated in lignin-derived carbon for efficient hydrogen evolution reaction

Molybdenum nickel alloy has been proved to be an efficient noble-metal-free catalyst for hydrogen evolution reaction(HER) in alkaline medium, but its electrocatalytic activity and stability need to be further improved to meet industrial requirements. In this study, carboxymethylated enzymatic hydrolysis lignin(EHL) was used as a biomacromolecule frame to coordinate with transition metal ions and reduced by pyrolysis to obtain the MoNi_(4)-NiO heterojunction(MoNi_(4)-NiO/C). The oblate sphere structure of MoNi_(4)-NiO/C exposed a large catalytic active surface to the electrolyte. As a result, the hydrogen evolution reaction of MoNi_(4)-NiO/C displayed a low overpotentials of 41 mV to achieve 10 mA cm-2and excellent stability of 100 h at 100 mA cm^(-2)in 1 mol L^(-1)KOH, which was superior to that of commercial Pt/C. Lignin assisted the formation of NiO to construct the MoNi_(4)-NiO interface and MoNi_(4)-NiO heterojunction structure, which reduced the energy barrier by forming a more favorable transition states and then promoted the formation of adsorbed hydrogen at the heterojunction interface through water dissociation in alkaline media, leading to the rapid reaction kinetics. This work provided an effective strategy for improving the electrocatalytic performance of noble-metal-free electrocatalysts encapsulated by lignin-derived carbon.

Microwave-assisted molybdenum-nickel alloy for efficient water electrolysis under large current density through spillover and Fe doping

The development of high-efficiency electrocatalysts for overall water splitting under large current density is significant and challenging.Herein,a high-performing Fe-doped MoNi alloy catalyst(M-H-MoNiFe-50)abundant with flower-like nanorods assemblies has been prepared by high-pressure microwave reaction and hydrogen reduction.Firstly,Fe doped NiMoO_(4) precursor(M-MoNiFe-50)was synthesized by microwave fast heating,ensuring the robustness of nanorods,which owns larger area and improved catalytic activity than that by conventional hydrothermal method.Secondly,M-MoNiFe-50 was reduced in H_(2)/Ar to fabricate Fe-incorporated MoNi_(4) alloys(M-H-MoNiFe-50),greatly enhancing the conductivity and facilitating hydrogen/oxygen spillover.The final M-H-MoNiFe-50 exhibits remarkable activity for alkaline/acidic hydrogen evolution reaction and oxygen evolution reaction with low overpotential of 208(alkaline),254(acid)and 347 mV at 1,000 mA·cm^(−2).Moreover,an alkaline water electrolyzer is established using M-H-MoNiFe-50 as anode and cathode,generating a current density of 100 mA·cm^(−2) at 1.58 V with encouraging durability of 50 h at 1,000 mA·cm^(−2).The extraordinary water splitting performance can be chalked up to the large surface area,favorable charge transfer,modified electron distribution,intrinsic robustness as well as an efficient gas spillover of M-H-MoNiFe-50.The final electrocatalyst has great prospects for practical application and confirms the significance of Fe doping,microwave method and spillover effect for catalytic performance improvement.