Study Of Cathodes For Hydrogen Evolution Reaction In Water Electrolysis

Hydrogen has attracted much attention as a kind of efficient,clean,ideal secondary energy.In particular,water electrolysis technique driven by renewable energy is supposed to be a clean and sustainable way for hydrogen production.However,the cathode materials display some obvious shortages such as high cost,excessive energy consumption and instability,which has restricted the development of water electrolysis and chlor-alkali industry.Therefore,it is of great significance to design and prepare an effective and inexpensive novel cathode with long-term durability.The recognition of the hydrogen evolution reaction?HER?mechanism is of critical importance for the rational design of HER electro-catalyst and a deeper fundamental understanding of the electro-catalytic theory.Therefore,the mechanism of HER was studied by analyzing the possible route of the reaction in different pH electrolytes.In addition,the catalyst with different activities at different applied potentials were assessed together to get a better catalyst with higher activity.Based upon the above process,a new catalyst with a low cost,good durability and high activity was invented.Firstly,the mechanism of HER on Pt electrode in different pH electrolyte solution with same ionic strength was investigated.The effect of overpotential on HER mechanism in different hydride ion?H+?concentration?i.e.pH?was investigated by using linear sweep voltammetry?LSV?and the current time lines of chronoamperometry?CA?.At the current density of 1mA·cm^-2 for HER,i.e.at a slight polarization,the overpotential of HER decreases along with the H+ concentration increasing in the concentration range between 0.1 mol·L^-1 and 0.01 mol·L^-1 HClO4 solution by LSV,while the overpotential of HER increases with the H+ concentration increasing in the 0.01 mol·L^-1 HClO4,dilute HClO4?<0.01M?solutions,0.1 mol·L^-1 KClO4 and KOH solutions.At the a relatively large current density of 5mA·cm^-2,i.e.at a slight higher polarization,the overpotential of HER increases with the H+ concentration increasing in the 0.01 mol·L^-1 HClO4,dilute HClO4(<0.01 mol·L^-1)solutions,0.1M KClO4 and KOH solutions.The relationship between overpotential of HER and H+ concentration in 0.01 mol·L^-1 HClO4 solution is the same with that in the dilute HClO4(<0.01 mol·L^-1),0.1 mol·L^-1 KClO4 and KOH solutions at the current density of 5mA·cm^-2 for HER.Thus the relationship of the hydrogen ion concentration with the HER kinetics is different at a lower overpotential from that at higher overpotential in 0.01 mol·L^-1 HClO4 solution.The results show that only H+ accepts electron to generate hydrogen in a concentrated H+ solution,such as 0.1 mol·L^-1 HClO4,and 0.01 mol·L^-1 HClO4?at lower overpotential?,while in 0.01 mol·L^-1 HClO4?at higher overpotential?,the dilute HClO4(<0.01 mol·L^-1),neutral KClO4 and KOH solutions,besides H+ accepts electron to generate hydrogen,water molecules also accept electrons to generate hydrogen.Based on a detailed analysis of the data,the electrocatalytic mechanism of the HER at different pH values on platinum in the same ionic strength was correlated with the potential,which could change the route of the hydrogen evolution reaction.Secondly,improvement in the efficiency and durability of the low cost electro-catalysts for HER is a permenant goal in electrolysis of water.Here,we address it by studying the activities of the HER on Ni-P,RuO₂ and RuO₂/Ni-P composite catalysts in alkaline medium.The Ni-P,RuO₂,and RuO₂/Ni-P composite were obtained by electrodeposition on the Ni plate by chronoamperometry.Scanning electron microscope?SEM?,energy dispersive X-ray spectroscopy?EDS?and X-ray photoelectron spectroscopy?XPS?analysis were used to confirm the composite components.The impedance measurements showed that Ni-P/Ni has lower value at high over potential and higher impedance at low over potential than RuO₂.We further found that the RuO₂/Ni-P/Ni electrode provide lower charge transfer impedance than the Ni-P/Ni and RuO₂/Ni both at low and high over potentials for HER.Thus RuO₂/Ni-P/Ni with less Ni-P and RuO₂ showed the highest catalytic activity for HER.Notably,the activity of the RuO₂/Ni-P/Ni electrode for HER could be enhanced by an electron charge transfer synergistic effect.Finally,the Ni-P alloy was electrodeposited on nickel to make four samples by using pulsed electrodeposition with 1#Ni-P/Ni 20000 cycles,2#Ni-P/Ni 40000 cycles,3#Ni-P/Ni 80000 cycles and 4#Ni-P/Ni 160000 cycles respectively.The electrodeposition of Ni-P alloy contains two periods in one cycle.Firstly,the negative current,I =-0.01 A,was applied for TON = 0.01s?TON—pulse-on-period?and then for TOFF = 0.01s?TOFF—pulse-off-period?.Secondly,the same current,I =-0.01 A,was applied for TON = 0.01 s and then for TOFF = 0.01 s.The 3#Ni-P/Ni already showed the highest electrocatalytic activity in the four Ni-P alloy samples.While the Ni-P alloy need higher overpotential to get higher activity.To get higher activity at low overpotential and steady durability,20000 Cycles pulsed electrodeposition of RuO₂ was performed on 3#Ni-P/Ni to make RuO₂/Ni-P/Ni.It could be confirmed that Ni-P,and RuO₂ were successfully deposited on the nickel plate by SEM,EDS and XPS analysis.RuO₂/Ni-P/Ni showed the highest activities.It presented four times higher catalytic performance for HER in alkaline than platinum plate at 0.2V overpotential.RuO₂/Ni-P/Ni electrode also showed much better durability than Ni-P samples.It was still bound on the nickel plate more tightly after the HER test for 22 h and exhibited more steady activity than 3#Ni-P/Ni.RuO₂/Ni-P/Ni electrode presents the current density of 325 mA·cm^-2 for HER in alkaline at the overpotential of 200 mV,which was four times higher than platinum plate(60 mA·cm^-2).