Electrocatalytic Reduction Of Nitrite To Ammonia In Environmental Water

Nowadays,with the development of technology and economy,the supply of fossil fuels has become more and more limited.Therefore,in order to promote the sustainable development of society,it is necessary to find renewable energy to replace fossil fuels.Ammonia（NH₃）as an economic,green and sustainable resource has attracted widespread attention.However,industrial ammonia synthesis not only relies on fossil fuels but also consumes a lot of energy,which is likely to make the the environment pollute greatly.The electrocatalytic synthesis of ammonia has been widely concerned because of its high efficiency,fast reaction and no pollution.On the other hand,as a common water-soluble nitrogen compound,nitrite（NO₂^-）is widely used as food additives and fertilizers in daily life.Nitrite pollution is also a serious water pollution problem because it is highly toxic to humans,animals and plants.Therefore,we urgently need to explore way to effectively remove nitrite.In this paper,the electrocatalytic nitrite reduction to ammonia by using active transition metal materials to achieve the production of ammonia and the removal of nitrite,which provides a feasible way to improve energy and environmental issues.The specific work is as follows:（1）Study on the performance of TiB₂ thin film electrocatalytic nitrite reduction to ammoniaThe TiB₂ thin film was prepared by magnetron sputtering,and then the TiB₂ thin film was characterized by X-ray diffraction（XRD）and scanning electron microscopy（SEM）.Chose the three-electrode system,where the working electrode was a TiB₂ thin film,the reference electrode was Ag/Ag Cl,and the counter electrode was a graphite rod.The test was carried out in a two-chamber electrolytic cell which contained 35 m L of 0.1 mol L^-1 PBS（phosphate buffer solution）and 0.1 mol L^-1 Na NO₂ solution in both the anode and cathode chambers.The research results showed that TiB₂ thin film has good performance of electrocatalytic nitrite reduction to ammonia.At the optimal potential of-0.5 V vs.RHE（reversible hydrogen electrode）,the TiB₂ thin film can achieve ammonia production rate as high as 565.2μgh^-1 cm^-2 and a Faraday efficiency of 88.4%was achieved.In addition,the blank control and precursor control experiments of TiB₂ thin film had also been further compared and verified that TiB₂ thin film has excellent electrocatalytic nitrite reduction to ammonia.The stability and selectivity experiments had also proved that TiB₂ thin film has excellent stability and selectivity.（2）Study on the performance of Fe₂P nanorod electrocatalytic nitrite reduction to ammoniaThe precursor Fe₂O₃ nanorod was synthesized by hydrothermal reaction,and then the precursor Fe₂O₃ nanorod was phosphatized at a high temperature of 300℃for two hours to synthesize Fe₂P nanorod,and then the Fe₂P nanorod was characterized by X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The performance of Fe₂P nanorod electrocatalytic nitrite reduction to ammonia at room temperature and normal pressure was studied.The research results showed that in the 35 m L of 0.1 mol L^-1 PBS（phosphate buffer solution）+0.1 mol L^-1 Na NO₂ electrolyte,at the optimal potential of-0.4 V vs.RHE（reversible hydrogen electrode）,the Fe₂P nanorod can achieve ammonia production rate as high as 2437.5μgh^-1 cm^-2 and a Faraday efficiency of 96.3%was achieved.In addition,the blank control and precursor control experiments of Fe₂P nanorod had also been further compared and verified that Fe₂P nanorod has excellent electrocatalytic nitrite reduction to ammonia.The stability and selectivity experiments had also proved that Fe₂P nanorod has good stability and selectivity.（3）Study on the performance of Ni₂P nanoarray electrocatalytic nitrite reduction to ammoniaThe precursor Ni（OH）₂ nanoarray was synthesized by hydrothermal reaction,and the precursor Ni（OH）₂ nanoarray was phosphatized at a high temperature of 280℃for two hours to synthesize Ni₂P nanoarray.It was characterized by X-ray mapping image（EDX）,high-resolution transmission electron microscope（HRTEM）,X-ray photoelectron spectroscopy（XPS）and other methods.The performance of Ni₂P nanoarray electrocatalytic reduction of nitrite to ammonia at room temperature and normal pressure was studied.The research results showed that in the 35 m L of 0.1 mol L^-1 PBS（phosphate buffer solution）+0.1 mol L^-1 Na NO₂ electrolyte,the Ni₂P nanoarray can achieve ammonia production rate of1526.2μgh^-1 cm^-2 and the Faraday efficiency up to 98.7%at the optimal potential of-0.4 V vs.RHE（reversible hydrogen electrode）.At the same time,a blank control and a precursor control were carried out to further verify that the Ni₂P nanoarray has good performance of electrocatalytic nitrite reduction to ammonia.The stability and selectivity experiments had also proved that Fe₂P nanorod has good stability and selectivity.