Mechanism Study Of Minerals And Carboxyl Functional Groups Effects On Coal Assisted Water Electrolysis

The realization of harnessing the abundant renewable energy source,such as wind or solar energy,is crucal to mitigate the aggravated global energy crisis and environmental pollution.Due to the characteristic of intermission and fluctuation,the scalable storage of those energy is required.Converting solar-or wind-derived electricity to H₂ via water electrolysis is an appealing means to accomplish those energy storage,as H₂ is a desirable media.However,water electrolysis is still an energy-intensive process preventing its practical application.Coal assisted water electrolysis?CAWE?,in which oxygen evolution reaction was replaced by coal oxidation at the anode,with part of the energy required for the electrolysis provided by chemical energy of coal,reduces the overall electrolysis energy input.And the co-storage of electric energy and chemical energy is realized.Nevertheless,the prohibitively low current density and low degradation degree of coal still exist as the problems related to this technology.And understanding the coal electrochemical oxidation mechanism throughly is the key to eliminate those obstacles.The understanding in distinguishing the oxidation of leached ions and organic structure was insufficient in acid media.To solve this problem,this work proposed to indentify the reaction paths by the onset potential in the LSV test.The experiment results indicate that the onset potential of H₂SO₄ electrolysis is 1.2 V,and the components of coal can induce lower water electrolysis onset potential.The current is attributed to Fe²⁺oxidation when the applied potential is above 0.5 V,and the oxidation of organic constituent should not be overlooked when the applied potential is higher than 0.8 V.The enhanced current density in the voltage range of 0.9–1.2 V is supposed to belonging to the oxidation of the soluble organic compounds.In potentiostatic tests,the AAEMs ions led to sustainable increased current density by activating coal particles at the constant potential of 2 V;while the transition metal ions,such as Fe²⁺,tend to show stronger catalytic effect at relatively low cell potential?1.4 V vs.SCE?.When the applied potential is 2 V,the reduction of Fe³⁺in surface of coal is the limiting step.The evolution of oxygen-containing functional groups on coal particles surface also played an important role in the electrolysis process.The key to the CAWE process is to oxidize the organic structure of coal compeletely for more chemical energy released.While the electrooxidation mechanism of the organic structure was researched insufficiently due to the complexity of carbon structure and functional groups.This work employs the graphite as the coal model compounds,and then loads the carboxyl functional groups on the surface of graphite particles.The results indicate that the carboxylated graphite?C+CO₂-24h?has high hydrophilicity and reactivity.Comparing to the H₂SO₄ electrolysis,C+CO₂-24h can reduce the onset potential for about 0.3 V.The high reaction temperation is favor to the electrooxidation of carboxyl.At 90^°C,the carboxyl functional groups can be completely oxidized to CO₂ at 1.72 V.When the Fe³⁺is used as the catalyst,Fe³⁺can oxidize the carboxyl functional groups quickly at 90^°C.According to the Fe³⁺concentration variation,this is a first order reaction.If the Fe³⁺and C+CO₂-24h slurry is pre-stirred for a long time at 90^°C,the voltage would drop to about 0.6 V.While the Fe³⁺reduction by the carboxyl functional groups on the surface of the graphite particles would be the limiting step when the applied current is high.And the lack of Fe²⁺results in the increase of the cell voltage.