The development of active and durable bifunctional electrocatalysts for overall water splitting is mandatory for renewable energy conversion. This study reports a general method for controllable synthesis of a class of IrM (M = Co, Ni, CoNi) multimetallic porous hollow nanocrystals (PHNCs), through etching Ir-based, multimetallic, solid nanocrystals using Fe ions, as catalysts for boosting overall water splitting. The Ir-based multimetallic PHNCs show transition-metal-dependent bifunctional electrocatalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic electrolyte, with IrCo and IrCoNi PHNCs being the best for HER and OER, respectively. First-principles calculations reveal a ligand effect, induced by alloying Ir with 3d transition metals, can weaken the adsorption energy of oxygen intermediates, which is the key to realizing much-enhanced OER activity. The IrCoNi PHNCs are highly efficient in overall-water-splitting catalysis by showing a low cell voltage of only 1.56 V at a current density of 2 mA cm , and only 8 mV of polarization-curve shift after a 1000-cycle durability test in 0.5 m H SO solution. This work highlights a potentially powerful strategy toward the general synthesis of novel, multimetallic, PHNCs as highly active and durable bifunctional electrocatalysts for high-performance electrochemical overall-water-splitting devices.

Application of transition metal phosphide (TMP) catalysts for full water splitting has great potential to help relieve the energy crisis. Various methods have been investigated to obtain high catalytic activity, but the use of electronic structure regulation by incorporation of different elements is of particular simplicity and significance for development of a universal TMP synthesis method. We herein describe a novel approach for fabricating a series of TMPs by pyrolyzing phytic acid (PA) cross-linked metal complexes. The introduction of oxygen atoms into TMPs not only enhanced their intrinsic electrical conductivity, facilitating electron transfer, but activated active sites via elongating the M-P bond, favoring the hydrogen evolution reaction (HER) or oxygen evolution reaction (OER). MoP exhibited relative low HER overpotentials of 118 mV and 93 mV while supporting a current density of 20 mA·cm in 0.5 M HSO and 1 M KOH electrolytes, respectively. When CoP was applied as a catalyst for OER, only 280 mV overpotential was required to reach current density of 10 mA·cm. Additionally, PA-containing precursors enabled intimate embedding of TMPs onto a flexible substrate surface (carbon cloth), so that electron injection from substrate and transport to the active sites was facilitated. Remarkably, an alkaline electrolyzer was able to achieve a current density of 40 mA·cm at the low voltage of 1.6 V, demonstrating its potential for practical overall water splitting without the use of noble metals.

The direct transformation of cellulose, which is the main component of lignocellulosic biomass, into building-block chemicals is the key to establishing biomass-based sustainable chemical processes. Only limited successes have been achieved for such transformations under mild conditions. Here we report the simple and efficient chemocatalytic conversion of cellulose in water in the presence of dilute lead(II) ions, into lactic acid, which is a high-value chemical used for the production of fine chemicals and biodegradable plastics. The lactic acid yield from microcrystalline cellulose and several lignocellulose-based raw biomasses is 460% at 463 K. Both theoretical and experimental studies suggest that lead(II) in combination with water catalyses a series of cascading steps for lactic acid formation, including the isomerization of glucose formed via the hydrolysis of cellulose into fructose, the selective cleavage of the C3-C4 bond of fructose to trioses and the selective conversion of trioses into lactic acid.