A notable trend in OER activity on transition metal phosphide pre-catalysts is reported. Remarkably, the tri-metallic FeCoNiP pre-catalysts exhibit exceptional apparent and intrinsic OER activities, outperforming many non-precious OER catalysts reported previously.

Synergistic coupling of ruthenium with cobalt phosphide can significantly boost the hydrogen evolution performance of the hybrid catalysts in a wide pH range.

Transition metal phosphides (TMPs) have recently emerged as an important type of electrode material for use in supercapacitors thanks to their intrinsically outstanding specific capacity and high electrical conductivity. Herein, we report the synthesis of bimetallic Co x Ni 1−x P ultrafine nanocrystals supported on carbon nanofibers (Co x Ni 1−x P/CNF) and explore their use as positive electrode materials of asymmetric supercapacitors. We find that the Co:Ni ratio has a significant impact on the specific capacitance/capacity of Co x Ni 1−x P/ CNF, and Co x Ni 1−x P/CNF with an optimal Co:Ni ratio exhibits an extraordinary specific capacitance/capacity of 3514 F g −1 /1405.6 C g −1 at a charge/discharge current density of 5 A g −1 , which is the highest value for TMP-based electrode materials reported by far. Our density functional theory calculations demonstrate that the significant capacitance/capacity enhancement in Co x Ni 1−x P/CNF, compared to the monometallic NiP/CNF and CoP/CNF, originates from the enriched density of states near the Fermi level. We further fabricate a flexible solid-state asymmetric supercapacitor using Co x Ni 1−x P/CNF as positive electrode material, activated carbon as negative electrode material, and a polymer gel as the electrolyte. The supercapacitor shows a specific capacitance/capacity of 118.7 F g −1 /166.2 C g −1 at 20 mV s −1 , delivers an energy density of 32.2 Wh kg −1 at 3.5 kW kg −1 , and demonstrates good capacity retention after 10000 charge/discharge cycles, holding substantial promise for applications in flexible electronic devices.

Proton exchange membrane water electrolysis (PEM-WE) has emerged as a promising technology for hydrogen production and shows substantial advantages over conventional alkaline water electrolysis. To enable efficient PEM-WE in acidic media, iridium (Ir)- or ruthenium (Ru)-based catalysts are indispensable to drive the thermodynamically and kinetically demanding oxygen evolution reaction (OER). However, developing Ir/Ru catalysts with high efficiency and long-term durability still remains a formidable challenge. Herein, we report one-pot hydrothermal synthesis of ultrafine IrRu intermetallic nanoclusters loaded on conductive, acid-stable, amorphous tellurium nanoparticle support (IrRu@Te). Benefiting from the large exposed electrocatalytically active surface of ultrafine IrRu clusters and the strong electronic coupling between IrRu and Te support, the as-obtained IrRu@Te catalysts show good catalytic performance for the OER in strong acidic electrolyte (i.e., 0.5 M H2SO4), requiring overpotentials of only 220 and 303 mV to deliver 10 and 100 mA cm–2 and able to sustain continuous OER electrolysis up to 20 h at 10 mA cm–2 with minimal degradation. Moreover, IrRu@Te exhibits high specific activity, illustrating intrinsically better performance compared with that of unsupported IrRu and other commercial Ir- and Ru-based catalysts. It also demonstrates unprecedentedly high mass activity of 590 A gIrRu –1 at an overpotential of 270 mV, outperforming most Ir- and Ru-based OER catalysts reported in the literature. Furthermore, IrRu@Te catalysts reveal good OER performance in neutral electrolyte as well, holding great potential to be used for PEM-WE in environmentally friendly conditions. Density functional theory (DFT) calculations based on oxidized IrRu confirm that the catalyst/support coupling results in a lower energy barrier for the oxygen–oxygen bonding formation, offering a rational explanation to the experimentally observed OER performance.

Hollow CoP octahedral nanoparticles have been prepared, and they show exceptionally high intrinsic activity for both the oxygen evolution and methanol oxidation reactions.

Achieving an efficient and stable oxygen evolution reaction (OER) in an acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (PEM-WE). Supported iridium-based nanoparticles (NPs) are the state-of-the-art OER catalysts for PEM-WE, but the nonhomogeneous dispersion of these NPs on the support together with their nonuniform sizes usually leads to catalyst migration and agglomeration under strongly corrosive and oxidative OER conditions, eventually causing the loss of active surface area and/or catalytic species and thereby the degradation of OER performance. Here, we design a catalyst comprising surface atomic-step enriched ruthenium–iridium (RuIr) nanocrystals homogeneously dispersed on a metal organic framework (MOF) derived carbon support (RuIr@CoNC), which shows outstanding catalytic performance for OER with high mass activities of 2041, 970 and 205 A gRuIr –1 at an overpotential of 300 mV and can sustain continuous OER electrolysis up to 40, 45, and 90 h at 10 mA cm–2 with minimal degradation in 0.5 M H2SO4 (pH = 0.3), 0.05 M H2SO4 (pH = 1), and PBS (pH = 7.2) electrolytes, respectively. Comprehensive experimental studies and density functional theory (DFT) calculations reveal that the good performance of RuIr@CoNC can be attributed, on one hand, to the presence of abundant atomic steps that maximize the exposure of catalytically active sites and lower the limiting potential of the rate-determining step of OER and, on the other hand, to the strong interaction between RuIr nanocrystals and the CoNC support that endows homogeneous dispersion and firm immobilization of RuIr catalysts on CoNC. The RuIr@CoNC catalysts also show outstanding performance in a single-cell PEM electrolyzer, and their large-quantity synthesis is demonstrated.

Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel. The two half-reactions of water splitting, that is, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), take place kinetically fast in solutions with completely different pH values. Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost, earth-abundant electrocatalysts is highly desirable but remains a challenge. Herein, we demonstrate that using a bipolar membrane (BPM) we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution, with bifunctional self-supported cobaltnickel phosphide nanowire electrodes to catalyze both reactions. Such asymmetric acid/alkaline water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA/cm 2 with ca. 100% Faradaic efficiency. Moreover, using an "irregular" BPM with unintentional crossover the voltage needed to afford 10 mA/cm 2 can be reduced to 0.847 V, due to the assistance of electrochemical neutralization between acid and alkaline. Furthermore, we show that BPM-based asymmetric water electrolysis can be accomplished in a circulated single-cell electrolyzer delivering 10 mA/cm 2 at 1.550 V and splitting water very stably for at least 25 hours, and that water electrolysis is enabled by a solar panel operating at 0.908 V (@13 mA/cm 2), using an "irregular" BPM. BPMbased asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis.

Alkaline water electrolysis is a cost-effective approach to hydrogen production, but it suffers from low operational current densities (typically ≤500 mA cm −2 ) and thereby a low hydrogen production rate. Herein we report the fabrication of self-supported porous cobalt phosphide (Co−P) foam by electrochemical anodization of commercially available cobalt foam, followed by thermal oxidation and subsequent phosphorization. The as-obtained porous Co−P foam, compared to other control samples prepared under different conditions, shows outstanding electrocatalytic performance in alkaline electrolyte for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), requiring an overpotential of 290 mV for HER and 380 mV for OER, respectively, at a high current density of 1000 mA cm −2 . Moreover, the electrolyzer consisting of two symmetric porous Co−P foam electrodes only requires a cell voltage of 1.98 V to operate at 1000 mA cm −2 for overall water electrolysis, with extraordinary stability of 4000 h, showing great potential for use in industrial alkaline water electrolysis.