Reversible current density

The other limiting case is that of an infinitely fast reaction, when the current is determined by transport only. It is customary to call such a reaction reversible, and denote the corresponding current density, which is determined by transport alone, as the reversible current density jrev. It is determined by the transport, usually by diffusion,... 

Fig. 4.11 Reverse current densities of moderately doped n-type (filled symbols) and p-type (open symbols) silicon electrodes in 3% HF and 1% HCI as a function of applied potential without illumination. The electrolyte was...

Fig. 6.56. Evolution of the electrical characteristics of the solar cells as a function of the duration of the surface treatment (Omin stands for no surface treatment) (a) Voc and FF, (b) Jsc and reverse current-density (/rev) measured at —2 V, (c) efficiency r). Reprinted with permission from [83]...

Fig.2. Current-density versus voltage (IV) characteristics of an Al/p-Si/PCBM/Al heterojunction at 295 K (top graph) and at 80 K (bottom graph). The inset shows an Arrhenius plot of the reverse current-density at -2 V bias. In the bottom graph the IV-characteristics at 80 K under broadband IR illumination (red triangles) is shown [2],...

The reversible potential, Ve, is the metal-solution potential difference when the net current density is zero. The forward and reverse current densities are equal at the reversible potential and are given by... 

The reaction rate, current density, is easy to measure. But note that this current density is a net current density, which is the difference between the forward and reverse current densities on the electrode. Generally, for a reaction in Equation 1.64, the net current density can be expressed as... 

In addition, if the Arrhenius equation applies, then the rate of film growth is described by the forward/reverse current densities at equilibrium... 

This model states that the corrosion rate on a metal surface is zero when the forward and reverse current densities become exactly the same at equilibrium E = Ecorr)- This criterion was recognized by Mears and Brown [3 in 1938 and it has become a common practice for protecting steel sUuctures. 

The usual expression for reverse current density in a diffusion limited diode is (e.g., [58])... 

At equilibrium, the rate of the forward reaction and that of reverse reaction are equal and j, the overall current density, is 0. However, j is composed of the forward current density, = nFvi, and the reverse current density, 72 = nFvi, both of which at equilibrium are equal to what is known as the exchange current density Jq. From Figure 2.2b, at equilibrium both the forward and reverse reactions have the same activation energy AG". Thus, the exchange current density is given by... 

Figure 1.1 Simple equivalent circuit (top) for modeling solar cell current-voltage characteristics and energy level diagram (bottom) mapping the various charge transfer processes in a DSSC to the current pathways of the model circuit. The dominant mechanisms are described by a current density Jl induced upon photoexcitation and electron injection into the conduction band of the metal oxide semiconductor surface MO, linear (Jsh) and nonlinear (/jj) reverse current densities in parallel with photocurrent source and a series resistance to account for electrode and ionic resistances. In Section 1.2.2 M0 = Ti02, Sn02, X = Br, I.

Reverse current density is important in deterrnining the power that a device consumes when in the off state as it determines the effective resistance of the device in reverse bias. Hence reverse current is also referred to as leakage current. From Equation 3.24, the reverse current is carried by drift of minority carriers from the lightly doped side of the junction (that is the side having the higher minority carrier density) toward the heavily-doped side. If one assumes a p -n diode (the p-type side is very heavily doped) then Equation 3.24 becomes ... 

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