Theoretical aspects of oxygen reduction and doped diamond

An ab initio approach to calculating activation energies for electrochemical processes and their potential dependencies is advanced. This methodology is applied to investigating the four steps of oxygen reduction to water in acidic media:; O2(g) + H+(aq) + e- → HOO·(aq) (1) HOO·(aq) + H+(aq) + e- → H2O2(aq) (2) H2O2(aq) + H+(aq) + e - → HO·(g) + H2O(l) (3) HO·(g) + H+(aq) + e- → H2O(l) (4) .;The proton is modeled by a hydronium ion solvated with two water molecules. An electron is transferred during reduction when the electron affinity of the reaction center matches the ionization potential of the modeled electrode. In the study of uncatalyzed reduction (Chapter 2), it is shown that the O 2 and H2O2 reduction steps have high calculated activation energies over the electrode potential range investigated. Bonding to platinum (Chapter 4) has the effect of decreasing them significantly. A parallel pathway going through the platinum oxide is established to be unlikely because it requires a higher activation. The issues of double layer potential drops and adsorbate bond polarizations are discussed for the case of inner-Helmholtz-plane processes. The extensions of the reaction model to include additional structure relaxations and to increase the solvation model are analyzed. A basis set and computational method analysis is explored (Chapter 3). This research demonstrates promise in using theory for studying the potential dependence of other electrochemical processes.;The electronic properties of impurities in diamond are examined by means of accurate, self-consistent field calculations (Chapter 5). Cluster models are used to determine the donor or acceptor abilities of a number of defects. The effects of surface termination on the band gap width and gap states are examined. Improvements of the cluster models by addition of diffuse functions, cluster solvation, and increasing the cluster size are considered.