No free lunch:
------------
| |
IIII|IIIII | Mg bias connection
II MMM II |
II II |
II II |
| II C II | | KEY:
| II C II | |
| II C II | | M - Mg bias anode
| II C II | | C - Cathode
| II C II | | A - Current supplying anode
| II C II | | II - Insulating dielectric
| II C II | |
| II C II | |
| II C II | |
(AC)----------| II C--------o----(-) Cathode potential
| II C II |
| II C II |
| II C II |
| II C II |----(-AC)
| II C II |
| II C II |
Plate 1 | II C II | Plate 2
| II C II |
| II C II |
II II
II AAAA II
IIIII|IIII
|
(+) Current Anode (Anode potential)
Fig. 1 - Diagram of Biased AC Electrolysis Cell
Top View, Cross section
Elecrolysis occurs on the left side of tha cathode during the positive
cycle for Plate 2, and the right side when Plate 1 is positive. The
electode "AAAA"is necessary to provide the net current which results - due
to current flowing when Plate 1 is positive and no current flowing when
Plate 1 is negative. Without the current anode or bias anode the cell is
merely an AC cell and insufficient loading occurs due to recombination.
Again deposition of Mg on the cathode may end the bias provided by the
sacrificial Mg anode. An alternative may be to use a Pt current providing
anode ("AAAA") which also provides the bias voltage (about 1.4 V) for the
AC. The bias voltage provided by "MMM" or "AAAA" is large enough to
sustain the cathode loading but small enough to avoid much evolved
hydrogen. In this arrangement the interface essentially acts like a diode,
an "incremental diode".
Unfortunately the current anode or bias anode supply the full cell current
i at the bias potential, i.e. about 1.4 V. The AC provides the current i
at the incremental voltage, so it appears there is no free lunch.
But wait a second. The AC portion does not have to push current through an
anode interface, so should save about half a volt over a regular
electrolytic cell. During the reverse cycle, assuming the AC peak
potential is less than 0.7 V, the cathode interface prevents current
flowing at all so the side of the cathode facing the negative cathode face
experiences no current, only the bias potential which holds hydrogen in the
cathode but does not evolve hydrogen. There may be an electrolysis
efficiency gain in this cell design? No free luch but maybe a free desert?
Regards,
Horace Heffner
