The visible-light-induced water oxidation ability of metal-ion-doped BiVO(4) was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO(4); Mo had the highest improvement by a factor of about six. Thus, BiVO(4) and W- or Mo-doped (2 atom %) BiVO(4) photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal-organic decomposition/spin-coating method. Under simulated one sun (air mass 1.5G, 100 mW cm(-2)) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (J(PH)) of about 2.38 mA cm(-2) was achieved for Mo doping followed by W doping (J(PH) ≈ 1.98 mA cm(-2)), whereas undoped BiVO(4) gave a J(PH) value of about 0.42 mA cm(-2). The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO(4) photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott-Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6-2 times higher, and a charge-transfer resistance reduced by 3-4-fold for W- or Mo-doped BiVO(4) relative to undoped BiVO(4). Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo-oxidation activity of water on BiVO(4) photoanodes (undoped

Atomic vacancies with controlled depth and size are generated on a graphite surface by lowenergy ion bombardment. The reactivity of vacancies towards an oxygen molecule is investigated by using scanning tunneling microscopy (STM) and density functional theory. An oxygen molecule (i) exothermally dissociates and then chemisorbs at the top sites and /or the bridge sites of a vacancy, or (ii) forms a precursor state of molecular oxygen at a bridge site. Reaction pathways for oxidative etching are proposed to interpret serpentine and circular etching patterns observed by STM.

Hydrogen has been touted as an energy carrier of the future because it combines with oxygen to produce only water with no greenhouse gases or other pollutants. For hydrogen to play the role, it must be produced in a sustainable manner from a renewable energy source, such as solar energy. [1] Unlike the electricity produced from the most common photovoltaic cells, hydrogen could store the solar energy in the form of chemical energy. One of the most attractive solar energy conversion reactions is the photoelectrochemical (PEC) or photocatalytic water splitting directly to H 2 and O 2 . Since its initial demonstration by Fujishima and Honda with a TiO 2 electrode under ultraviolet light, [2] there has been steady progress in this field in search of semiconductor photocatalytic electrode materials that work under visible light irradiation for ample solar light absorption. However, the photocatalysts with high efficiency, durability, and economic feasibility are still elusive. [3,4] Scheelite-monoclinic BiVO 4 (mBiVO 4 ) is a well-known photocatalyst, which absorbs visible light owing to a suitable band-gap energy (E g % 2.4 eV). [5,6] It is also nontoxic and chemically stable in aqueous solution under irradiation. However, pristine mBiVO 4 usually shows a low photocatalytic activity owing to poor charge-transport characteristics [7] and the weak surface adsorption properties. [8] Numerous attempts have been made to improve the photocatalytic activity of BiVO 4 , including heterojunction structure formation, [7,9,10] loading co-catalysts, [11][12][13] and impurity doping. [8,14,15] Impurity doping, that is, the addition of a small percentage of foreign atoms in the regular crystal lattice of semiconductors, produces dramatic changes in their electrical properties by increasing their electron or hole densities. In photocatalysis by BiVO 4 , for example, doping with molybdenum to replace a small fraction of vanadium was found to improve the photocatalytic activity for water oxidation. [8,14,15] Phosphorus is a typical dopant for silicon or germanium to make it an n-type semiconductor. However, it has been rarely used as dopant for semiconductor photocatalysts. This is rather surprising because other non-metallic elements, such as N, C, and S, have been widely used as anionic dopants for photocatalysts to reduce their band-gap energies. [16] In the present work, for the first time we doped phosphorous into the vanadium sites in the host lattice of BiVO 4 , replacing some of the VO 4 oxoanions in BiVO 4 with PO 4 oxoanions. Oxoanion doping into the photocatalyst is to the best of our knowledge also a new concept. Herein we report effects of PO 4 oxoanion doping on the photoelectrochemical or photocatalytic behavior of mBiVO 4 under visiblelight illumination. The PO 4 oxoanion doping did not bring about significant changes in the optical absorption behavior and crystal structure of mBiVO 4 . When an appropriate amount PO 4 oxoanion was doped, however, the activity of photoelectrochemical water oxidation increased very sign...

Controlling extra charge carriers is pivotal in manipulating electronic, optical, and magnetic properties of various two-dimensional materials. Nonetheless, the ubiquitous hole doping of two-dimensional materials in the air and acids has been controversial in its mechanistic details. Here we show their common origin is an electrochemical reaction driven by redox couples of oxygen and water molecules. Using real-time photoluminescence imaging of WS2 and Raman spectroscopy of graphene, we capture molecular diffusion through the two-dimensional nanoscopic space between two-dimensional materials and hydrophilic substrates, and show that the latter accommodate water molecules also serving as a hydrating solvent. We also demonstrate that HCl-induced doping is governed by dissolved O2 and pH in accordance with the Nernst equation. The nanoscopic electrochemistry anatomized in this work sets an ambient limit to material properties, which is universal to not only 2D but also other forms of materials.

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