Decoration of boron nanoparticles on a graphene sheet for ammonia production from nitrate

Abstract

Clean water and sanitation are two of the most important challenges worldwide and the main source for freshwater is groundwater. Nowadays, water is polluted by human activities. Concern about the presence of nitrates (NO₃⁻) in groundwater is increasing day-by-day due to the intensive use of fertilizers and other anthropogenic sources, such as sewage or industrial wastewater discharge. Thus, the main solution available is to remove NO₃⁻ from groundwater and transfer it back to a usable nitrogen source. Electrochemical reduction of NO₃⁻ to ammonia (NH₃) under ambient conditions is a highly desirable method and it needs an efficient electrocatalyst. In this work, we synthesized a composite of amorphous boron with graphene oxide (B@GO) as an efficient catalyst for the nitrate reduction reaction. XRD and TEM analysis revealed an amorphous boron decoration on the graphene oxide sheet, and XPS confirmed that no bonding between boron and carbon occurs. In B@GO, a stronger defect carbon peak was observed than in GO and there was a random distribution of boron particles on the surface of the graphene nanosheets. Amorphous boron exhibits a higher bond energy, more reactivity, and chemical activity toward nitrate ions, which could be due to the lone pair present in the B atoms and could also be due to the edge oxidized B atoms. B@GO has a high number of active sites exposed leading to excellent nitrate reduction performance with a faradaic efficiency of 61.88% and good ammonia formation rate of 40006 μg h⁻¹ m_cat⁻¹ at −0.8 V versus reversible hydrogen electrode.