Hydrogen Overvoltage lowering

An interesting field of application is the protection of tantalum against hydrogen embrittlement by electrical connection to platinum metals. The reduction in hydrogen overvoltage and the shift of the free corrosion potential to more positive values apparently leads to a reduced coverage by adsorbed hydrogen and thereby lower absorption [43] (see Sections 2.1 and 2.3.4). 

Pressure at elevated pressures, the value of the hydrogen overvoltage changes only very slightly but at lower pressures, it increases sharply on certain metals, as for example in the case of copper, nickel, and mercury cathodes. 

These data pertain to reductions on mercury only. On other metals, the reduction potential may be shifted to more negative values, and since the hydrogen overvoltage would be lower, the onium ions might not reduce preferentially. We speculate, however, that the order of reducibility would not be changed in comparisons on a given substrate. This does seem to be a reasonable approximation for sulfonium salts at least (11). 

Ni, Co, and Fe codeposit with Zn. They will lower the hydrogen overvoltage and initiate cyclic zinc deposition and redissolution. 

Brine purity requirements for the mercury cell are more strict, since traces of transition metal ions can cause severe process upset by lowering the hydrogen overvoltage on mercury. Simple adsorption of interfering ions onto the precipitated calcium and magnesium floes will normally achieve sufficient control. Iron is simultaneously precipitated as the hydroxide (Eq. 8.8). If this is inadequate. 

This equation reduces to Eh = -4.308 x 10 5T ln/n, i.e. Eh = -0.029 log/h at 20°C, where 0.98 bar hydrogen pressure would result from a hydrogen overvoltage of 29 mV. It is interesting to note that maximum embrittlement occurs here at a fugacity of 108 (i.e./fj = 104) compared with the much lower value of/h = 104 found for AISI 4340 steel by Scully and Moran,9 i.e. a martensitic microstructure is more readily embrittled by cathodic polarization than the duplex. 

Tokuyama Soda has developed. The hydrogen overvoltage of LHOC surface is 150-200 mV lower than carbon steel. Electrolysis power consumption of the 10,000 mt/year plant electrolysis is 2400-2500 KWH/mt NaOH at 2 KA/m using steel cathodes. Using... 

Hoar and Bucklow (1) recently indicated that the hydrogen overvoltage in a citrate buffer solution for both tungsten and cobalt at 3 to 4 ma/cm is 0.1 volt. For a tungsten-cobalt alloy it is much lower. It would be interesting to determine whether the alloy is also a better catalyst for hydrogen atom recombination than either cobalt or tungsten. 

All proteins yield catalytic hydrogen waves ( presodium waves ) at the negative end of polarograms by lowering the hydrogen overvoltage as discovered by Heyrovsky and Babicka in 1939. Moreover, in 1933 Brdicka introduced the catalytic double waves in the presence of cobalt ions which... 

A black phosphorus electrode [7, 30] has a low hydrogen overvoltage, and electrolysis in aqueous solution is accompanied by reduction of the cathode material with formation of phosphane. The largest PH3 yield of 27.5% (calculated from the loss of the electrode weight) at 12.5% current efficiency was obtained in 1M K2HPO4 (pH 7.5) at a current density of 0.07 to 0.09 A/cm2 and at 20 C. Altering the pH to either the acidic or basic side reduces the PH3 yield. An increase in catholyte temperature from 20 to 55 0 lowers the PH3 yield by a factor of 5 to 6. Decreasing the current density also lowers the current efficiency [30]. 

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