Electrocatalysis of oxygen reduction and small alcohol oxidation in alkaline media

Abstract

We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.

Reaction mechanism for methanol oxidation on Au(111): A density functional theory study

“…Surprisingly, methanol will dissociate on the oxygen-covered Au surface to form a variety of oxidation products and intermediates, namely methoxy, formaldehyde, formate, methyl formate, CO, CO 2 , and H 2 O [21][22][23][24][25]. But different products were observed depending on different experimental conditions.…”

“…During the past two decades, numerous efforts have been devoted to developing the catalytic activity of gold for different purposes, for instance, the use of fuel cells [2], synthesis of esters, olefin epoxidation [3][4][5][6][7][8], and selective oxidation of alcohols [9][10][11][12][13][14][15][16][17][18][19][20]. Among them, alcohol oxidation is of particular interest since it is not only one of the most important reactions in industry and organic synthesis, but also one that Au-based catalysts carry out most efficiently.…”

Developments in electrode materials and electrolytes for aluminium–air batteries

“…The oxygen reduction reactivity of MnO x in a coin-type Aleair cell has been compared against that of platinum for galvanostatic discharge at 0.4 mA using aluminium powder as the anode [137]. The choice of electrolyte, a KOH/ethanol mixture for this comparison was not appropriate because ethanol is oxidised by platinum to form carbon dioxide [118,138]. The discharge density for the button cell with the MnO x catalyst was 512 W h kg À1 -Al, which is a fraction of the theoretical specific energy of 8100 W h kg À1 -Al of an aluminium anode [137].…”

“…A platinum catalysed air electrode would be unsuitable for use with methanol or ethanol electrolytes, as they are oxidised by platinum releasing carbon dioxide gas [118,138]. Alternative catalysts, such as tungsten carbideesilver composite (AgeW 2 C/C) [166] and a La 0.6 Ca 0.4 CoO 3 perovskite have been successfully used for the reduction of oxygen in alkaline alcohol/water mixtures [156].…”

“…Air cathode technology has been reviewed for PEM fuel cell [112,113], metaleair cell [111,114e117] and alkaline fuel cell applications [118,119], and will not be considered in detail here.…”