Multihole water oxidation catalysis on hematite photoanodes revealed by operando spectroelectrochemistry and DFT

Water oxidation is the key kinetic bottle neck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi-redox reactionon metal-oxidephotoanodes remains a significant experimental and theoretical challenge. Here we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly upon hematite.We observe that hematite is able toaccess a reaction mechanism third order in surface hole density, assigned to equilibration between three surface holes and M(OH)-O-M(OH) sites. This reaction exhibits a remarkably low activation energy (Ea~ 60 meV). Density functional theory is employedto determine the energetics of charge accumulation and O-O bond formation on a modelhematite 110 surface. The proposed mechanism shows parallels with the function of oxygen evolving complex of photosystem II,and provides new insights to the mechanism of heterogeneous water oxidation on a metal oxide surface

Partner-Level Factors Associated with Insertive and Receptive Condomless Anal Intercourse Among Transgender Women in Lima, Peru

Condomless anal intercourse among transgender women (TW) in Peru has been shown to vary by the type of partner involved (e.g. primary vs. casual vs. transactional sex partner), but no previous studies have explored variations in partner-level patterns of condom use according to type of anal intercourse. We evaluated the relationship between partnership characteristics and condom use during insertive (IAI) versus receptive anal intercourse (RAI) among TW with recent, non-female partners. Condomless IAI was more common with transactional and casual sex partners and by TW who self-reported HIV-uninfected serostatus (p<0.05), alcohol use disorders, or substance use before sex. Condomless RAI was more common with primary partners and by TW who described their HIV serostatus as unknown (p<0.05). Examining partner-level differences between condomless IAI and RAI reveals distinct patterns of HIV/STI risk among TW, suggesting a need for HIV prevention strategies tailored to the specific contexts of partners, practices, and networks