After carbon, hydrogen, and oxygen, nitrogen is the next most abundant element in the human body. Inorganic and organic compounds of nitrogen feature prominently in many biological and environmental, as well as industrial, processes. In nature, the inorganic compounds of nitrogen are controlled by a reaction cycle called the nitrogen cycle (Figure 1).1 The denitrification pathway in this cycle, that is, the conversion of nitrate to dinitrogen, is employed by certain bacteria to produce ATP anaerobically and gain energy for cell growth. All organisms use ammonia as one of the starting building blocks for the synthesis of amino acids, nucleotides, and many other important biological compounds. Nitric oxide is * Corresponding author. E-mail: m.koper@chem.leidenuniv.nl. † Present address: Energy research Centre of The Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands. ‡ Present address: Research, Development & Innovation, AkzoNobel Chemicals bv, Velperweg 76, P.O. Box 9300, 6800 SB Arnhem, The Netherlands. Chem. Rev. 2009, 109, 2209–2244 2209

Nitrogen cycle electrocatalysis.

Underpotential deposition at single crystal surfaces of Au, Pt, Ag and other materials

Electrochemical oxide film formation at noble metals as a surface-chemical process

Nitrate contamination in surface and ground waters is one of this century’s major engineering challenges due to negative environmental impacts and the risk to human health in drinking water. Electrochemical reduction is a promising water treatment technology to manage nitrate in drinking water. This critical review describes the fundamental principles necessary to understand electrochemical reduction technologies and how to apply them. The focus is on electrochemical nitrate reduction mechanisms and pathways that form undesirable products (nitrite, ammonium) or the more desirable product (dinitrogen). Factors influencing the conversion rates and selectivity of electrochemical nitrate reduction, such as electrode material and operating parameters, are also described. Finally, the applicability for treating drinking water matrices using electrochemical processes is analyzed, including existing implementation of commercial treatment systems. Overall, this critical review contributes to the understanding of the potential applications and constraints of electrochemical reduction to manage nitrate in drinking waters and highlights directions for future research required for implementation.

Electrocatalytic reduction of nitrate: Fundamentals to full-scale water treatment applications

Electrocatalytic reduction of nitrate at low concentration on coinage and transition-metal electrodes in acid solutions

Role of adsorption phenomena in the electrocatalytic reduction of nitric acid at a platinized platinum electrode

Radiotracer study of the adsorption of Cl− and HSO4− ions on a porous gold electrode and on underpotential deposited metals on gold

Electrocatalytic reduction of NO2− and NO3− ions at a platinized platinum electrode in alkaline medium

Radiotracer study of adsorption phenomena on copper electrodes. Study of the adsorption of chloride ions and thiourea on "copperized" electrodes

Radiotracer study of the adsorption of phosphoric acid on platinized platinum electrodes in the presence of different ions and oxalic acid

E.M. Rizmayer

Papers

Role of adsorption phenomena in the electrocatalytic reduction of nitric acid at a platinized platinum electrode

Radiotracer study of the adsorption of Cl− and HSO4− ions on a porous gold electrode and on underpotential deposited metals on gold

Electrocatalytic reduction of NO2− and NO3− ions at a platinized platinum electrode in alkaline medium

Radiotracer study of adsorption phenomena on copper electrodes. Study of the adsorption of chloride ions and thiourea on "copperized" electrodes

Radiotracer study of the adsorption of phosphoric acid on platinized platinum electrodes in the presence of different ions and oxalic acid