Unravelling Hydrogen Adsorption Kinetics on Ir(111)Electrode in Acid Solutions by Impedance Spectroscopy

The kinetics for hydrogen(H)adsorption on Ir(111)electrode has been studied in both HClO_(4) and H_(2)SO_(4) solutions by impedance spectroscopy.In HClO_(4),the adsorption rate for H adsorption on Ir(111)increases from 1.74×10^(-8)mol·cm^(-2)·s^(-1) to 3.47×10^(-7)mol·cm^(-2)·s^(-1) with the decrease of the applied potential from 0.2 V to 0.1 V(vs.RHE),which is ca.one to two orders of magnitude slower than that on Pt(111)under otherwise identical condition.This is explained by the stronger binding of water to Ir(111),which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network.In H_(2)SO_(4),the adsorption potential is ca.200 mV negatively shifted,accompanied by a decrease of adsorption rate by up to one order of magnitude,which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111).Our results demonstrate that under electrochemical environment,H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.

A review of defect engineering in two‐dimensional materials for electrocatalytic hydrogen evolution reaction

The exploration of efficient and earth‐rich electrocatalysts for electrochemical reactions is critical to the implementation of large‐scale green energy conversion and storage techniques.Two‐dimensional(2D)materials with distinctive structural and electrochemical properties provide fertile soil for researchers to harvest basic science and emerging applications,which can be divided into metal‐free materials(such as graphene,carbon nitride and black phosphorus)and transition metal‐based materials(such as halogenides,phosphates,oxides,hydroxides,and MXenes).For faultless 2D materials,they usually exhibit poor electrochemical hydrogen evolution reaction(HER)activity because only edge sites can be available while the base surface is chemically inactive.Defect engineering is an effective strategy to generate active sites in 2D materials for improving electrocatalytic activity.This review presents feasible design strategies for constructing defect sites(including edge defects,vacancy defects and dopant derived defects)in 2D materials to improve their HER performance.The essential relationships between defect structures and electrocatalytic HER performance are discussed in detail,providing valuable guidance for rationally fabricating efficient HER electrocatalysts.The hydrogen adsorption/desorption energy can be optimized by constructing defect sites at different locations and by adjusting the local electronic structure to form unsaturated coordination states for efficient HER.

Vertically mounting molybdenum disulfide nanosheets on dimolybdenum carbide nanomeshes enables efficient hydrogen evolution

Designing hierarchical heterostructure to optimize the adsorption of hydrogen intermediate(H*)is impressive for hydrogen evolution reaction(HER)catalysis.Herein,we show that vertically mounting two-dimensional(2D)layered molybdenum disulfide(MoS_(2))nanosheets on 2D nonlayered dimolybdenum carbide(Mo_(2)C)nanomeshes to form a hierarchical heterostructure largely accelerates the HER kinetics in acidic electrolyte due to the weakening adsorption strength of H*on 2D Mo_(2)C nanomeshes.Our hierarchical MoS2/Mo2C heterostructure therefore gives a decrease of overpotential for up to 500 mV at-10 mA·cm^(-2)and an almost 200-fold higher kinetics current density compared with the pristine Mo2C nanomeshes and maintains robust stability with a small drop of overpotential for only 16 mV upon 5,000 cycles.We further rationalize this finding by theoretical calculations and find an optimized adsorption free energy of H*,identifying that the MoS_(2)featuring strong H*desorption plays a key role in weakening the strong binding of Mo_(2)C with H*and therefore improves the intrinsic HER activity on active C sites of Mo_(2)C.This present finding shines the light on the rational design of heterostructured catalysts with synergistic geometry.