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The electrocatalytic properties of nanoparticles depend on their size, shape and composition. These properties are typically probed by measuring the total electrocatalytic reaction current of a large number of nanoparticles, but this approach is time-consuming and can only measure the average catalytic activity of the nanoparticles under study. However, the identification of new catalysts requires the ability to rapidly measure the properties of nanoparticles synthesized under various conditions and, ideally, to measure the electrocatalytic activity of individual nanoparticles. Here, we show that a plasmonic-based electrochemical current-imaging technique can simultaneously image and quantify the electrocatalytic reactions of an array of 1.6 × 10(5) platinum nanoparticles printed on an electrode surface, which could facilitate high-throughput screening of the catalytic activities of nanoparticles. We also show that the approach can be used to image the electrocatalytic reaction current and measure the cyclic voltammograms of single nanoparticles.

Herein, we present a new strategy for the synthesis of 2D porous MoP/Mo2N heterojunction nanosheets based on the pyrolysis of 2D [PMo12O40]3−‐melamine (PMo12‐MA) nanosheet precursor from a polyethylene glycol (PEG)‐mediated assembly route. The heterostructure nanosheets are ca. 20 nm thick and have plentiful pores (<5 nm). These structure features offer advantages to promote the HER activity, including the favorable water dissociation kinetics around heterojunction as confirmed by theoretical calculations, large accessible surface of 2D nanosheets, and enhanced mass‐transport ability by pores. Consequently, the 2D porous MoP/Mo2N heterojunction nanosheets exhibit excellent HER activity with low overpotentials of 89, 91 and 89 mV to achieve a current density of 10 mA cm−2 in alkaline, neutral and acidic electrolytes, respectively. The HER performance is superior to the commercial Pt/C at a current density >55 mA cm−2 in neutral medium and >190 mA cm−2 in alkaline medium.

The hydrogen evolution reaction (HER) in the neutral medium can avoid the problems caused by strong acid (bases) media and thus is promising for practical application. The suitable catalyst in the neutral medium for HER requires good conductivity for decreasing ohm resistance, porous structures for weakening diffusion resistance, and plentiful active sites, but its synthesis remains a challenge. Here, the 2D MoP/MoS 2 heterostructure nanosheets rather than common anion doping supported on carbon cloth (CC) was designed to meet the above criteria. The catalyst only needs a low overpotential of 96 mV to achieve a current density of 10 mA cm −2 (η 10 ) for HER in the neutral medium (without iR correction), which is much lower than 199 mV of the bare MoS 2 . The good performance is ascribed to plentiful active sites on the heterointerface of MoP/MoS 2 for activating H 2 O, good conductivity of MoP and CC for electron transfer, and pores surrounded by MoP/MoS 2 facilitating mass transfer as shown by XPS and density functional theory calculations. The catalyst also exhibits outstanding activity in alkaline (η 10 of 54 mV) and acid (η 10 of 69 mV) media. The cells by coupling the MoP/MoS 2 cathode with a NiFe-LDH anode can deliver a current density of 10 mA cm −2 at 1.51 V in 1 M KOH and 1.98 V in 1 M PBS. The effective overall water splitting can be driven by a solar panel (1.51 V), implying its ability to store solar energy as H 2 energy.

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