Can we offer voluntary prayers as charity/sadaqah, so that Allah removes our difficulties?

I have heard a hadith which says that indeed, sadaqah/charity postpones/removes a coming adversity. I have also heard that we can offer voluntary prayer (like 2 nafl) as sadaqa (even though I have not been able to find an authentic reference from Quran or hadith). These days I am going through a lot of trials, one after the other (which encompasses monetary and valuables' loss, multiple incidents of theft, problems at work place, health issues). So I want to give charity, so that Allah, by His grace and mercy, removes upcoming difficulties and make it easy for me inshaAllah. The question is that since I am short of cash at the moment, can I offer nafl/voluntary prayers as sadaqa?