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

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

Oxidation of alcohols with molecular oxygen on platinum metal catalysts in aqueous solutions

In situ infrared studies of glucose oxidation on platinum in an alkaline medium

In situ Fourier transform infrared reflection absorption spectroscopic studies of glucose oxidation on platinum in acid

This paper reports rotating ring-disk electrode techniques employed for the investigation of the electrocatalytic reduction of nitrate induced by underpotential-deposited cadmium on Au and Ag surfaces. Based on Albery's kinetic analysis it has been concluded that for concentrations of nitrate in the millimolar range, the reaction products depend on the {ital p}H of the solution. Specifically, for {ital p}H = 3, the reaction yields predominantly nitrite, whereas for {ital p}H = 1, the process proceeds beyond the nitrite stage to generate products which do not undergo oxidation on a Au ring electrode polarized at potentials as high as 1.0V {ital vs.} SCE. Additional evidence in support of these results was provided by exhaustive bulk electrolysis experiments. The lack of linearity of some of Albery's diagnostic plots could be accounted for quantitatively by a numerical integration of the differential equations which govern disproportionation-type reactions at rotating ring electrodes. Good agreement was found between theory and experiment using independently determined values for the rate constant of disproportionation of NO{sub 2} in solution.

The Electrocatalytic Reduction of Nitrate Mediated by Underpotential‐Deposited Cadmium on Gold and Silver Electrodes in Acid Media

A modified scanning tunneling microscopy (STM) was used in situ to examine the changes in the surface topography induced by the underpotential deposition of a monolayer of lead on Au(111). Comparison of the STM images before and after deposition shows that an essentially conformal layer of lead covers the gold substrate. However, pit sites and terrace boundaries display topographic changes due to additional lead-on-lead bonding at step edges.

Xuekun Xing

Papers

In situ infrared studies of glucose oxidation on platinum in an alkaline medium

In situ Fourier transform infrared reflection absorption spectroscopic studies of glucose oxidation on platinum in acid

The Electrocatalytic Reduction of Nitrate Mediated by Underpotential‐Deposited Cadmium on Gold and Silver Electrodes in Acid Media

In situ scanning tunneling microscopy studies of the underpotential deposition of lead on Au(111)

Electrochemical oxidation of nitrite on a rotating gold disk electrode: a second-order homogeneous disproportionation process