Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co-Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized CoMnCH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm for HER can be also achieved on CoMnCH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional CoMnCH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis.

Well-defined pomegranate-like N,P-doped Mo 2 C@C nanospheres were prepared by simply using phosphomolybdic acid (PMo 12 ) to initiate the polymerization of polypyrrole (PPy) and as a single source for Mo and P to produce N,P-doped Mo 2 C nanocrystals. The existence of PMo 12 at the molecular scale in the polymer network allows the formation of pomegranate-like Mo 2 C@C nanospheres with a porous carbon shell as peel and Mo 2 C nanocrystals welldispersed in the N-doped carbon matrix as seeds. This nanostructure provides several favorable features for hydrogen evolution application: (1) the conductive carbon shell and matrix effectively prevent the aggregation of Mo 2 C nanocrystals and facilitate electron transportation; (2) the uniform N,P-doping in the carbon shell/matrix and plenty of Mo 2 C nanocrystals provide abundant catalytically highly active sites; and (3) nanoporous structure allows the effective exposure of active sites and mass transfer. Moreover, the uniform distribution of P and Mo from the single source of PMo 12 and N from PPy in the polymeric PPy−PMo 12 precursor guarantees the uniform N-and P-co-doping in both the graphitic carbon matrix and Mo 2 C nanocrystals, which contributes to the enhancement of electrocatalytic performance. As a result, the pomegranate-like Mo 2 C@C nanospheres exhibit extraordinary electrocatalytic activity for the hydrogen evolution reaction (HER) in terms of an extremely low overpotential of 47 mV at 10 mA cm −2 in 1 M KOH, which is one of the best Mo-based HER catalysts. The strategy for preparing such nanostructures may open up opportunities for exploring low-cost highperformance electrocatalysts for various applications.

A binder-free efficient MoNi /MoO nanorod array electrode with 3D open structure is developed by using Ni foam as both scaffold and Ni source to form NiMoO precursor, followed by subsequent annealing in a reduction atmosphere. It is discovered that the self-templated conversion of NiMoO into MoNi nanocrystals and MoO as dual active components dramatically boosts the hydrogen evolution reaction (HER) performance. Benefiting from high intrinsic activity, high electrochemical surface area, 3D open network, and improved electron transport, the resulting MoNi /MoO electrode exhibits a remarkable HER activity with extremely low overpotentials of 17 mV at 10 mA cm and 114 mV at 500 mA cm , as well as a superior durability in alkaline medium. The water-alkali electrolyzer using MoNi /MoO as cathode achieves stable overall water splitting with a small cell voltage of 1.6 V at 30 mA cm . These findings may inspire the exploration of cost-effective and efficient electrodes by in situ integrating multiple highly active components on 3D platform with open conductive network for practical hydrogen production.