A systematic structural elucidation of the near-surface active species of the two remarkably active nickel phosphides Ni12P5 and Ni2P on the basis of extensive analytical, microscopic, and spectroscopic investigations is reported. The latter can serve as complementary efficient electrocatalysts in the hydrogen (HER) versus oxygen evolution reaction (OER) in alkaline media. In the OER Ni12P5 shows enhanced performance over Ni2P due to the higher concentration of nickel in this phase, which enables the formation of an amorphous NiOOH/Ni­(OH)2 shell on a modified multiphase with a disordered phosphide/phosphite core. The situation is completely reversed in the HER, where Ni2P displayed a significant improvement in electrocatalytic activity over Ni12P5 owing to a larger concentration of phosphide/phosphate species in the shell. Moreover, the efficiently combined use of the two nickel phosphide phases deposited on nickel foam in overall electrocatalytic water splitting is demonstrated by a strikingly low cell voltage and high stability with pronounced current density, and these catalysts could be an apt choice for applications in commercial alkaline water electrolysis.

Cu-functionalized carbon nitride nanoparticles (Cu-g-CN NPs), ∼200 nm, and Cu-carbon dots (Cu-C-dots), ∼8 nm, act as horseradish peroxidase-mimicking catalysts. The nanoparticles catalyze the generation of chemiluminescence in the presence of luminol/HO and catalyze the oxidation of dopamine by HO to form aminochrome. The Cu-g-CN-driven generation of chemiluminescence is used to develop a HO sensor and is implemented to develop a glucose detection platform and a sensor for probing glucose oxidase. Also, the Cu-C-dots are functionalized with the β-cyclodextrin (β-CD) receptor units. The concentration of dopamine, at the Cu-C-dots' surface, by means of the β-CD receptor sites, leads to a 4-fold enhancement in the oxidation of dopamine by HO to yield aminochrome compared to that of the unmodified C-dots.

The strikingly high catalytic performance and stability of manganese substituted cobalt oxide spinel (MnCoO) over pristine cobalt oxide spinel (CoO) for the alkaline electrochemical water oxidation is reported. The different role of cations could be uncovered along with the detection of drastic surface-structural changes during the catalysis using spectroscopic and microscopic methods.

A highly active FeSe electrocatalyst for durable overall water splitting was prepared from a molecular 2Fe-2Se precursor. The as-synthesized FeSe was electrophoretically deposited on nickel foam and applied to the oxygen and hydrogen evolution reactions (OER and HER, respectively) in alkaline media. When used as an oxygen-evolution electrode, a low 245 mV overpotential was achieved at a current density of 10 mA cm , representing outstanding catalytic activity and stability because of Fe(OH) /FeOOH active sites formed at the surface of FeSe . Remarkably, the system is also favorable for the HER. Moreover, an overall water-splitting setup was fabricated using a two-electrode cell, which displayed a low cell voltage and high stability. In summary, the first iron selenide material is reported that can be used as a bifunctional electrocatalyst for the OER and HER, as well as overall water splitting.

Nickel-manganese oxides with variable Ni : Mn ratios, synthesised from heterobimetallic single-source precursors, turned out to be efficient water oxidation catalysts. They were subjected to oxidant-driven, photo- and electro-catalytic water oxidation showing superior activity and remarkable stability. In addition, a structure-activity relation could be established.