Encouraged by the great promise of heteroatoms-doped carbon materials for catalyzing the oxygen reduction reaction (ORR) in fuel cells, phosphorus-doped carbon has exhibited high catalytic activity for the ORR. Here, by means of comprehensive density functional theory (DFT) computations, we explored the relationships among the catalytic activity, stability, and the local chemical bonding states at dopant sites of P-doped graphene sheets for ORR to identify the most optimized P-doped graphene structure. The structures show that the P atom can substitute one or two C atoms to form P-doped graphene structures with three or four P–C bonds (PC3G or PC4G), respectively, and these structures are easily oxidized into the OPC3G and OPC4G models with P–O bond. The further calculations reveal that the stability, band structure, surface charge distribution, potential active sites, and free energy of the rate-determining step of P-doped graphene can be modulated effectively by the chemical bonding states of P atom and the formation of C–P–O bond. The OPC3G model is the most effective and stable P-doped graphene for ORR due to its stability, activity, and the amount of the potential active sites. Another significant finding is that the C atoms possessed high negative charge, which also can be the optimal active sites for ORR. Our work provides useful guidance for the rational design and fabrication of P-doped graphene framework and helpful further activity enhancement.

The sluggish kinetics of the oxygen evolution reaction (OER) is the bottleneck of water electrolysis for hydrogen generation. Developing cost-effective OER materials with a high value of practical application is a prerequisite to achieve extreme performance in both activity and stability. Herein, we report a “dual ligand synergistic modulation” strategy to accurately tune the structure of transition-metal materials at atomic level, which finally achieves satisfactory results for the unity between robust stability and high activity. Remarkably, the elaborately designed S and OH dual-ligand NiCo2(SOH)x catalyst exhibits an excellent OER activity with a very small overpotential of 0.29 V at a current density of 10 mA cm–2 and a strong durability even after 30 h accelerated aging at a large current density of 100 mA cm–2, both of which are superior to most of the state-of-the-art OER catalysts so far. The density functional theory (DFT) calculations disclose that the synergy of OH and S ligands on the surface of NiCo2(SOH)x can delicately tune the electronic structure of metal active centers and their chemical environment, which results in optimal binding energies of the OER intermediates (*OH, *O, and *OOH) and a strengthened binding energy between metal and anion ligands, thus leading to an excellent intrinsically enhanced OER activity and stability, respectively. Meanwhile, the special nonmagnetism of NiCo2(SOH)x can significantly weaken the resistance of O2 desorption on the catalyst surface, thus facilitating the O2 evolution proceedings.Keywords: DFT calculation; dual-ligand modulation; electrocatalysis; magnetism; oxygen evolution;

Au is a chemically inert metal, while Os is quite active to react with oxygen. Although Au and Os are in the two extremes in chemical properties, unexpectedly, both of them can enhance the oxygen reduction reaction (ORR) activity of Pt-based alloys. In this work, a systematical density functional theory calculation was used to elucidate the mechanisms of enhanced activity in PtM/Pd with doped atoms changing from chemically inert Au to active Os. The calculations show that different sites on the PtAu/Pd and the PtOs/Pd surface adopt different ORR mechanisms due to the heterogeneous electronic structures, such as uneven surface charge and unequal d-band center. More importantly, all of the ORR steps on the sites far away from the doped atoms in the PtAu/Pd and PtOs/Pd display similar activation energy corresponding to better catalytic activity than the other sites. The catalytic activity is mainly affected by the ligand effect, and a proper distance between the doped atoms and the Pt atoms should induce the catalysts to possess the highest catalytic activity. These results also uncover why the different content of doped atom can lead to the different activity of catalysts.

We rationally designed and controllably fabricated a well-defined porous nitrogen-doped carbon nanotube with open-ended channels as a catalyst for the ORR by a twice pseudomorphic transformation of MnO2 nanotubes. The as-prepared O-NCNT catalysts exhibit an expectably remarkable performance, indicating the potential for replacing Pt-based catalysts in fuel cells and metal–air batteries.

Developing highly efficient catalysts for the oxygen reduction reaction (ORR) is key to the fabrication of commercially viable fuel cell devices and metal–air batteries for future energy applications. Herein, we review the most recent advances in the development of Pt-based and Pt-free materials in the field of fuel cell ORR catalysis. This review covers catalyst material selection, design, synthesis, and characterization, as well as the theoretical understanding of the catalysis process and mechanisms. The integration of these catalysts into fuel cell operations and the resulting performance/durability are also discussed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.

In this study, an inexpensive electrocatalyst, Ni-doped Mo2C nanowires, were grown directly on Ni foam via a hydrothermal reaction combined with a carburization process. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and linear scanning voltammetry (LSV) were used to scrutinize the catalysts and their electrochemical performance. The results showed that the designed NiMo2C/NF catalyst displays enhanced catalytic activity toward hydrogen production with a low onset overpotential of 21 mV. For driving a cathodic current density of 100 mA cm−2, it only needs an overpotential of 150 mV. Such excellent performance of NiMo2C/NF could be ascribed to the high intrinsic activity from a synergistic function of Ni and Mo2C, as well as to the exposure of more Ni-doped Mo2C sites provided by the high aspect ratio of a one-dimensional (1D) structure and rich surface area.

We synthesize the ultrathin MoS2 nanosheets perpendicular to reduced graphene oxides (MoS2⊥RGO) as an electro-catalyst, which exhibits excellent catalytic activity and good stability for the hydrogen evolution reaction (HER) in acidic medium.

Surface Al leached Ti3AlC2 particles (e-TAC) with high corrosion resistance and excellent electrical conductivity were developed as an advanced support material for Pt catalysts. Electrochemical measurements confirm that the supported Pt/e-TAC electrocatalyst shows much improved activity and enhanced durability toward the oxygen reduction reaction when compared with the commercial Pt/C catalyst.

A solvent evaporation plus hydrogen reduction (SE-HR) method is developed for the synthesis of carbon supported IrNi nanoparticles (IrNi/C) by using ammonia as a complexing agent. In this method, well distributed Ni(NH3)nIrCl6 complexes are formed and adsorbed on the carbon support; after thermal annealing, highly dispersed IrNi nanoparticles are obtained by in situ reduction of the corresponding complexes. By varying the preparation conditions, IrNi/C samples with the lattice parameter of Ir controlled in the range from 3.8416 Å to 3.6649 Å are prepared. The hydrogen oxidation reaction (HOR) of the IrNi/C exhibits volcano-shaped dependence on the lattice parameter of Ir with a maximum activity at 3.7325 Å. The mass activity of the as-synthesized catalysts is higher than or comparable to that of commercial Pt/C catalysts in the three-electrode test and single cell test. The high activity is ascribed to the optimal interaction between the catalyst surface and the hydrogen intermediates, and to the high specific electrochemical activity surface area resulting from the novel SE-HR method.

Faster oxygen transport is critical to guarantee reliable power output of polymer electrolyte membrane fuel cells (PEMFCs). In order to enhance oxygen transfer in a porous electrode especially in the case of water flooding, water-proof oil (dimethyl-silicon-oil (DMS)) was introduced into the conventional Pt/C electrode. Owing to the capability of electrochemical impedance spectroscopy (EIS) in discriminating individual contribution of ohmic, kinetic, and mass transport from all PEMFC processes, EIS was carried out to evaluate the effect of the DMS on the oxygen reduction reaction (ORR). The equivalent circuits corresponding to the EIS spectra were employed. The parameters in the equivalent circuits were obtained by curve fitting to the EIS spectra with the aid of the frequency response analysis software (FRA) attached in the electrochemical station Autolab PGSYAT302. The EIS analysis has shown that the introduction of DMS reduces the oxygen diffusion resistance as well as the charge transfer resistance in the flooded state. The single cell tests show that even in the case of normal operating condition the accumulated water with PEMFC operation also worsens the oxygen transfer in the conventional Pt/C gas diffusion electrode (GDE) with more and more water produced at the cathode. GDE containing DMS, which is defined as a flooding tolerant electrode (FTE), is fortunately quite good at alleviating water flooding. Success of the FTE in alleviating water flooding is ascribed to (1) its high oxygen transfer flux due to the higher solubility of oxygen in DMS than in water as long as parts of pores are occupied beforehand by DMS rather than by water, and (2) enhanced hydrophobic property of the FTE with DMS adsorption on the walls of the pores, which makes more hydrophobic pores be open to oxygen transport.Highlights► Water-proof oil – dimethyl-silicon-oil (DMS) used for increasing flooding tolerance of a conventional Pt/C gas diffusion electrode (GDE). ► The introduction of DMS into the GDE observably decreased the oxygen diffusion resistance and indirectly lowers the charge transfer resistance of the ORR. ► Success of the FTE in alleviating water flooding lies in (1) the higher solubility of oxygen in DMS than in water and (2) the enhanced hydrophobic property of the pores with DMS adsorption, which makes more hydrophobic pores open to oxygen transport.

Ultra low Pt-loading and high Pt utilization electrodes were prepared by displacement of electrodeposited Cu on a porous carbon electrode. Copper particles were electrodeposited on a porous carbon electrode (PCE) by four-step deposition (FSD) at first. The size and dispersion of deposited Cu particles were markedly improved with application of the FSD. The Cu deposits were then displaced by platinum as dipping a Cu/PCE in a platinum salt solution. Sequentially, Pt particles supported on the PCE were obtained. The Pt/PCE electrode prepared via the FSD of Cu overcomes the problem of the hydrogen evolution reaction accompanied with direct platinum electrochemical deposition, and has a high Pt dispersion. The single cell consisting of the electrodes Pt/PCE via the FSD of Cu outputs a power of 0.45 W cm−2 with ultra low Pt loadings of 0.196 mg cm−2 MEA (0.098 mg cm−2 per each side of the MEA) at no backpressure of reactant gases.

To avoid carbonation of small organic molecule oxidation in alkalines by using noble metals in acid, as well as to keep the proton transfer capability of polyaniline (PAn) in an acidic medium, we investigated formic acid oxidation on PAn-supported Pd catalysts in a weak acid solution of (NH4)2SO4. PAn was electrochemically polymerized on porous carbon electrodes (PCE) and glass carbon electrodes (GCE) to form electrodes PAn/PCE and PAn/GCE, on which Pd particles were deposited by electrochemical deposition. The properties of fabricated electrodes were examined electrochemically with the aid of a scanning electron microscope and a Fourier transform infrared spectroscope. Formic acid oxidation on the electrode Pd/PAn/PCE has been proven to undergo direct oxidation of weakly reactive or nonadsorbed intermediates to form CO2. The synergistic effect of Pd, PAn, and carbon powders was proposed to explain the enhanced oxidation of formic acid on the electrode Pd/PAn/PCE.

A solvent evaporation plus hydrogen reduction (SE-HR) method is developed for the synthesis of carbon supported IrNi nanoparticles (IrNi/C) by using ammonia as a complexing agent. In this method, well distributed Ni(NH3)nIrCl6 complexes are formed and adsorbed on the carbon support; after thermal annealing, highly dispersed IrNi nanoparticles are obtained by in situ reduction of the corresponding complexes. By varying the preparation conditions, IrNi/C samples with the lattice parameter of Ir controlled in the range from 3.8416 Å to 3.6649 Å are prepared. The hydrogen oxidation reaction (HOR) of the IrNi/C exhibits volcano-shaped dependence on the lattice parameter of Ir with a maximum activity at 3.7325 Å. The mass activity of the as-synthesized catalysts is higher than or comparable to that of commercial Pt/C catalysts in the three-electrode test and single cell test. The high activity is ascribed to the optimal interaction between the catalyst surface and the hydrogen intermediates, and to the high specific electrochemical activity surface area resulting from the novel SE-HR method.

In this study, an inexpensive electrocatalyst, Ni-doped Mo2C nanowires, were grown directly on Ni foam via a hydrothermal reaction combined with a carburization process. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and linear scanning voltammetry (LSV) were used to scrutinize the catalysts and their electrochemical performance. The results showed that the designed NiMo2C/NF catalyst displays enhanced catalytic activity toward hydrogen production with a low onset overpotential of 21 mV. For driving a cathodic current density of 100 mA cm−2, it only needs an overpotential of 150 mV. Such excellent performance of NiMo2C/NF could be ascribed to the high intrinsic activity from a synergistic function of Ni and Mo2C, as well as to the exposure of more Ni-doped Mo2C sites provided by the high aspect ratio of a one-dimensional (1D) structure and rich surface area.

Developing highly efficient catalysts for the oxygen reduction reaction (ORR) is key to the fabrication of commercially viable fuel cell devices and metal–air batteries for future energy applications. Herein, we review the most recent advances in the development of Pt-based and Pt-free materials in the field of fuel cell ORR catalysis. This review covers catalyst material selection, design, synthesis, and characterization, as well as the theoretical understanding of the catalysis process and mechanisms. The integration of these catalysts into fuel cell operations and the resulting performance/durability are also discussed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.

We synthesize the ultrathin MoS2 nanosheets perpendicular to reduced graphene oxides (MoS2⊥RGO) as an electro-catalyst, which exhibits excellent catalytic activity and good stability for the hydrogen evolution reaction (HER) in acidic medium.