History of Electro-chemistry - a meeting to mark the bicentenary of Humphry Davy's taking up the Professorship of Chemistry at the Royal Institution

23 March 2001, The Royal Institution

The meeting was organised jointly by the Royal Institution, the Historical Group of the Royal Society of Chemistry, and the Society for the History of Alchemy and Chemistry. Speakers were Professor David Knight, Dr Frank James, and Dr Mary Archer.

David Knight called his paper, "New understanding, new elements: Davy's electrochemistry". Gravity is universal; but chemical affinity is elective - some substances react together and others don't. In 1800, chemistry had recently acquired a new vocabulary and a theory of burning from Antoine Lavoisier but awaited its Newton, who would explain affinity simply, in terms of forces. Then Alessandro Volta announced that when two different metals are separated by wet cardboard, an electric current flows. Davy (1778-1829), a young Cornishman working in Bristol, believed that this could not be due to mere contact - a chemical reaction must be generating electricity. Appointed, in 1801 to the Royal Institution in London, Davy attracted audiences that maintained his research laboratory.

At first made to work on tanning and agriculture, by 1806 Davy could undertake blue skies research. When wires from a big version of Volta's battery were dipped into water, oxygen and about twice its volume of hydrogen bubbled around them. Davy was sure that the ratio should be exact (as when water was formed), without by-products. Using apparatus of silver, gold and agate, he confirmed this hunch; concluding that electricity and chemical affinity were manifestations of one power. Researching in autumnal bursts, the following year he tried using electric currents to break down other substances, notably caustic potash and soda. With molten potash and sparks flying, he obtained globules of a light and highly reactive 'potagen' like the alchemists' long-sought alkahest. He danced about the laboratory in ecstatic delight. Experiments on the soft material, which floated on water, bursting into flames, convinced him that it was a metal; and he renamed it 'potassium'. From soda, he obtained the analogous sodium, afterwards isolating calcium and other metals also. More systematic chemists, J.J.Berzelius and Davy's assistant Michael Faraday, brought new order into chemistry by developing Davy's Newtonian insight that affinity was electrical.

Frank James' paper was entitled "….'a model to teach him what he should avoid': Faraday and Davy's electro-chemistry". Faraday's knowledge of electro-chemistry derived from Davy - very early on during the European tour they tried to use electricity from a torpedo to decompose water electro-chemically. In the 1820s Faraday was involved in Davy's unsuccessful project to protect ships bottoms electro-chemically. It was debacles such as this that presumably prompted Faraday to remark to Henry Bence Jones that in Davy he had "a model to teach him what he should avoid". Indeed, electro-chemistry was not a major concern of Faraday's until 1831, when he discovered electromagnetic induction. He needed to establish the identity of all forms of electricity. As he developed better ways of producing electricity from magnetism he continued, unsuccessfully at first, to show that it could produce electro-chemical decomposition.

The early 1830s was a very creative period for Faraday. In Series 5 of Experimental Researches on Electricity, he criticised the two-fluid theory of electricity and also previous theories of electro-chemical action. replacing this with a theory of 'internal corpuscular action'. In Series 6, dated 30 November 1833, he developed a sophisticated atomic/molecular theory. Almost immediately afterwards he started the experiments for what would become Series 7 in which he drew back from the atomic theory in an abrupt manner - maybe with Davy's example in mind. He quickly decided that his new theory required a new language with which to express it and adopted the terms anode, cathode, anion and cation, and ion. Within this framework that Faraday enunciated his laws of electrolysis, although his first law had been stated in an earlier form in Series 3. He also withdrew into a severely operational view of electro-chemistry, by, for the first time, publicly attacking the atomic theory. Faraday's electro-chemical work thus played a crucial role in turning him away from the atomic theory, and set him on a path that would culminate ultimately in the field theory of electro-magnetism.

Mary Archer's paper, entitled "Beyond metal electrodes, Semiconductors, space charge layers and surface states", brought the meeting right up to date in an area of contemporary electrochemistry; an area in which Dr Archer herself worked at the Royal Institution with George Porter.

After pointing out that some of the early workers were unwittingly using semiconductor electrodes because of the contamination of metal surfaces with oxide or sulphide layers, Dr Archer outlined some key historical landmarks. She commenced with Edmond Becquerel's observation of 1839 of a photoelectrochemical effect using a platinum electrode coated with silver halide. Other key events included the double layer at metal electrodes (Gouy and Chapman 1910), the band structure of solids (Brillouin, 1920s), the theory of electrolyte solutions (Debye and Hückel, 1923), metal-semiconductor junctions (Schottky 1938), the point-contact transistor (Bardeen and Brattain, 1947), and the electronic structure of doped transistors (Shockley, 1949).

Dr Archer then contrasted the space-charge layers existing at a metal electrode-solution interface and a semiconductor-electrode-solution interface. The early semiconductor electrode research was complicated by impurities, but work in the Bell Telephone Laboratories reduced these difficulties, with the production of high quality doped germanium. Ensuing key events included Brattain, Garrett and Dewald's work on the principles of semiconductor electrochemistry (1960), Gerischer's work in the 1960s on the kinetics of electron transfer between valence and conduction bands, the photoelectrolysis of water (Fujishima and Honda, 1972), and the early demonstrations of solar photoelectrochemistry by Memming, Heller and Lewis in 1974. More recent developments resulted in efficient (12%) photoelectrochemical water splitting by Turner in 1999.

Dr Archer then outlined the mechanism of photoeffects at electrodes, showing how an illuminated n-type semiconductor drives an oxidation process, and a p-type semiconductor a reduction process. Surface states - crystalline defects or islands of platinum on a semiconductor surface - can be a nuisance or can promote the desired reaction. Such electrodes hold out prospects for the photo-oxidation of pollutants such as PCBs. The photosensitisation of semiconductor electrode surfaces presents problems - a monolayer of dye gives poor light absorption, a thick layer quenches the desired reaction, but a nanocrystalline sensitised layer on glass may be the solution. Dr Archer concluded by outlining some current and possible future applications. These included various solar energy conversion devices, and the prospect of light-activated self-cleaning surfaces consisting of a bed of semiconductor particles and titanium dioxide. Organic surface contaminants would be oxidised, and wiping down the kitchen tiles might no longer be necessary!

John Hudson, Hon Secretary, SHAC
Anglia Polytechnic University